Hindawi Publishing CorporationThe Scientific World JournalVolume 2013 Article ID 254376 10 pageshttpdxdoiorg1011552013254376

Research ArticleUnstart Coupling Mechanism Analysis of Multiple-ModulesHypersonic Inlet

Jichao Hu1 Juntao Chang2 Lei Wang1 Shibin Cao1 and Wen Bao1

1 School of Energy Science and Engineering Harbin Institute of Technology Harbin 150001 China2 Academy of Fundamental and Interdisciplinary Sciences Harbin Institute of Technology Harbin 150001 China

Correspondence should be addressed to Juntao Chang changjuntaohiteducn

Received 24 August 2013 Accepted 19 September 2013

Academic Editors S W Chen and M G Perhinschi

Copyright copy 2013 Jichao Hu et alThis is an open access article distributed under theCreativeCommonsAttribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The combination of multiplemodules in parallel manner is an important way to achieve the much higher thrust of scramjet engineFor the multiple-modules scramjet engine when inlet unstarted oscillatory flow appears in a single-module engine due to highbackpressure how to interact with each module by massflow spillage and whether inlet unstart occurs in other modules areimportant issuesTheunstarted flowfield and coupling characteristic for a three-module hypersonic inlet caused by centermodule IIand side module III were conducted respectivelyThe results indicate that the other two hypersonic inlets are forced into unstartedflow when unstarted phenomenon appears on a single-module hypersonic inlet due to high backpressure and the reversed flowin the isolator dominates the formation expansion shrinkage and disappearance of the vortexes and thus it is the major factorof unstart coupling of multiple-modules hypersonic inlet The coupling effect among multiple modules makes hypersonic inlet bemore likely unstarted

1 Introduction

The performance of a ramjetscramjet powered hypersonicvehicle is determined by its inlet efficiency Specificallythe inlet shock wave system influences the compressionefficiency mass capturing and combustion stability Unstartphenomenon is one of the most important issues of hyper-sonic inlets For hypersonic air-breathing engines inletunstart causes a large drop both engine thrust and specificimpulse and thus it may cause catastrophic damage duringhypersonic flight [1] The hypersonic inlet unstart can begenerated by either the design factors (such as large inter-nal area-contract ratios and serious shockboundary-layerinteractions) or the operation conditions (such as low flightMach number large angle of attack and high backpressure)It is a challenge to ensure that a hypersonic inlet is alwaysstarted In the existing flight tests including CIAMNASAin 1999 [2] Hypersonic Collaborative AustraliaUnited StatesExperiment in 2008 [3] X-51A in 2011 [4] inlet unstartoccurred due to various reasons Therefore inlet unstartshould be studied deeply and seriously

There have beenmany papers devoted to hypersonic inletunstart while most of literature studies treat it as a steadystate flow phenomenon [5ndash9] Yu et al [5ndash7] discussed thefeature selection and pattern classification of hypersonicinlet startunstart based on numerical and experimental dataChang et al [8] studied the effect of boundary layer bleedingon unstartrestart characteristics of hypersonic inlet Only afew papers [10ndash13] considered it as an unsteady flow phe-nomenonusing some transient testingmethods Tan et al [13]firstly investigated the oscillatory flow of hypersonic inletscaused by the downstreammassflow choking and the resultssuggest that hypersonic inlets usually suffer from violentshock wave system oscillations prominent pressure fluctu-ations and abrupt performance reductions when unstartedphenomenon appears Furthermore the surface pressureshows a significant periodic pressure oscillation during theprocess of hypersonic inlet buzz which causes unsteadyaerodynamic loads And they are highly detrimental to thestructural safety of scramjets and the flight control of vehicles

Multiple-modules in parallel manner are an importantway to achieve the much higher thrust for scramjet engines

2 The Scientific World Journal

30 15 0minus15 0 50 100 150 200 250 300 350 400 450 500 550 600

X (mm)

Z (mm)

Y(m

m)

120100

80604020

Cross-sectionY

Cross-section Z3

Module III Module IModule II

(a)

L1 L2 L3 L4

L

H

5

L6

1205751

1205752

1205753

1205754

1205755

(b)

Figure 1 The 3D view of multiple-modules hypersonic inlet and geometric parameters

The modular nature facilitates engine scaling An enginecan be easily scaled by adding more flowpaths withoutrequiring fueling redistribution because each flowpath isidentical In addition scaling in this manner does not changethe boundary-layer characteristics relative to the flowpathgeometry Aerojet conducted this multiple-modules strutjetengine [14] in this parallel manner The advantage of usingthis approach is that each module is independent and thegeometry and flowfield of scramjet engine are not needed tobe redesigned and it is beneficial to the rapid prototyping ofscramjet engine

Formultiple-modules engines when inlet unstart appearsin a single-module engine due to high backpressure howto interact with each module by the massflow spillage andwhether inlet unstart phenomenon occurs in other modulesare important issues and they are also the investigationemphasis of this paper To discuss this problem inlet modeland numerical method are given in Section 2 Section 3 pre-sents some typical simulation results and analysis Section 4presents some conclusions

2 Inlet Model and Numerical Method

21 Inlet Model The 3D view of a multiple-modules hyper-sonic inlet is presented in Figure 1 The duct of the multiple-modules hypersonic inlet is separated into three modulesmodule I module II and module III

Table 1 Geometric parameters of the hypersonic inlet

1198711m 119871

2m 119871

3m 119871

4m 119871

5m 119871

6m

0212 0113 0106 0169 0144 0048Hm 120575

1∘ 120575

2∘ 120575

3∘ 120575

4∘ 120575

5∘

0015 6 83 98 13 141

The multiple-modules hypersonic inlet is designed asa mixed-compression type including three external shocksand two internal shocks The main geometric parametersof the hypersonic inlet are referred to Figure 1 and Table 1and the length unit is m and the angle unit is degree Thedeflection angle of the three external ramps is 6∘ 83∘and98∘ respectively and the deflection angle of the internal rampand cowl tip is 10∘ and 141∘ respectively These compressionramps can guarantee the formation of a set of similar strengthshock The external contraction ratio and internal one are547 and 129 so the total one is 705

To show and analyze the flowfield structure convenientlyin Section 3 some typical cross-sections are defined Cross-section 1198851 cross section 1198852 and cross section 1198853 parallel to119883119884 plane and their values of119885-axis areminus75mm 75mm and225mm respectively Cross section119884parallels119883119885plane justlocated at the inlet entrance These typical cross sections will

The Scientific World Journal 3

(a) Simulation results (Mach number contour) (b) Experimental results

Figure 2 Comparison between Mach number contour and Schlieren pictures of a started inlet

t = 0ms

t = 1ms

t = 2ms

t = 3ms

t = 4ms

t = 5ms

(a) Simulation results (Mach number contour)

t998400= 5ms

t998400= 0ms

t998400= 1ms

t998400= 2ms

t998400= 3ms

Slipping layer

t998400= 4ms

t998400= 5ms

(b) Experimental results

Figure 3 Comparison between Mach number contour and Schlieren pictures in a big buzz cycle

be used to analyze the unstart coupling mechanism of themultiple-modules hypersonic inlet

22 Numerical Method The computation is performedusing the finite-volume technique with upwind discretiza-tion to solve the three-dimensional compressible Reynolds-Averaged Navier-Stokes equations The fluid was modeledas a single-specie thermally perfect air The piecewise-polynomial method was selected to compute specific heatwhile viscosity was solved using Sutherlandrsquos formulaThe space discretization is performed by a cell-centered for-mulationThe advection upstream splitting method (AUSM)flux vector splitting is applied for the approximation ofthe convective flux functions Higher-order accuracy forthe upwind discretization and consistency with the centraldifferences used for the diffusive term is achieved by the

monotonic upstream scheme for conservation laws extrap-olations and the total variation diminishing property of thescheme is ensured by the Van Leer flux limiter For transientsimulations the governing equations must be discretized inboth space and time Temporal discretization involves theintegration of every term in the differential equations over atime step Time integration is performed by an implicit fivestage Runge-Kutta time-stepping scheme in the computationand the advantage of the fully implicit scheme is that it isunconditionally stable with respect to time step size

The computations have been performed using a struc-tured grid An excellent quality all-quad 3D mesh with2000 k control volumes is generated for the simulation andensuring the maximum 119910+ was below 10 required for usingwith Shear-Stress Transport (SST) turbulence mode whichis found to be the feasible turbulence model option for

4 The Scientific World Journal

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

05 ms

(c)

01

02 03 04 05 06

05 ms

(d)

01

02 03 04 05 06

20 ms

(e)

01

02 03 04 05 06

20 ms

(f)

01

02 03 04 05 06

40 ms

(g)

01

02 03 04 05 06

40 ms

(h)

01

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

45 ms

(i)

01

02 03 04 05 06

45 ms

05 10Mach number

20 3015 25 35 4540

(j)

Figure 4 Mach contours mixing with streamlines of cross section 1198851 (1198853) and 1198852 in a buzz cycle

the simulation of vortices embedded in a boundary layerFor the steady simulation the mass conservation is checkedby measuring the mass-flow rate error In general 05 erroris a good indicator for convergence

The boundary condition of the supersonic inflow is far-pressure field and the freestream conditions can be defined

by specifying the boundary conditions The boundary con-dition of the exit of the isolator is the pressure outlet andthe backpressure can be defined by changing the throttlingarea shown in Figure 1 At solid walls the no-slip boundarycondition is enforced by setting the velocity components tozero

The Scientific World Journal 5

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

0 2 4 6 8 10 12 140

01

02

03

04

05

06

07

Module IModule IIModule III

(a) Mass-captured coefficient

Module IModule IIModule III

0 2 4 6 8 10 12 140

05

1

15

2

25

Time (ms)

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 5 The histories of mass-captured coefficient and static pressure at the exit of isolator

23 Numerical Accuracy Analysis Firstly comparison of aSchlieren picture [13] without throttling and correspondingMach number contour lines of the computation is shown inFigure 2 and it reveals an overall good agreementThe shockwave pattern the separation and the approximate boundary-layer thickness of the Schlieren picture are also present inthe simulation results Secondly comparison of a Schlierenpicture [13] with higher throttling ratio and correspondingMach number contour lines of the computation is shown inFigure 3 At a higher throttling ratio the hypersonic inletbuzz appears It can be seen that during a big buzz cyclethe inlet flow patterns exhibit a series of striking changes incontrast with a little buzz The external compression shocksystem is first destroyed and then reestablished the entranceseparation bubble is first disgorged and then swallowed andthe shock train in the isolator is first developed and thendispelled

As discussed above the comparison between the sim-ulation and experimental results shows that the simulationresults accord with the physical conception of the aerody-namics and can reveal the primary characteristics of startedand unstarted hypersonic inlet

3 Results and Discussion

Whether inlet unstart phenomenon occurs or not dependson the mass flow rate balance between inlet entrance andcombustor exit If Mach number of the freestream is loweror the combustor backpressure is higher inlet unstart wouldappear For the multiple-modules hypersonic inlet on theone hand the difference of forebody shock compression ofeach module hypersonic inlet and the variation of angleof attacksideslip angle all lead to the nonuniform of the

flowfield at the entrance of isolators on the other hand thecombustion oscillation or deflagration all result in that thepressure at the exit of isolators shows uneven In contrast witha single-module engine the factors discussed above increasethe matching difficulty between the inlet and combustorcharacteristics for multiple-modules scramjet engines Theemphasis of this paper is to investigate the unstart couplingmechanism of multiple-modules hypersonic inlet due to thebackpressure of a single-module hypersonic inlet especiallyon how to interact with eachmodule by themassflow spillage

31 Unstarted Flowfield Structure Caused by Module II Throt-tling Firstly the unstarted flowfield structure caused bymodule II throttling was investigated Because the contour ofcross section 1198851 is the same as that of cross section 1198853 onlyone of them is presented Mach number contours of crosssection 1198851 and 1198852 in a buzz cycle are shown in Figure 4

As can be seen from the figure of 119905 = 0ms in Figure 4inlet is started though a small separated bubble is formed inentranceThe separated bubble is termed as ldquoinitial separatedbubblerdquo in order to facilitate the description below Theflowfield structure of the multiple-modules hypersonic inletgoes through four stages as follows

Stage I MassFilling Up (0sim05ms) A high pressure region isformed at the exit of module II due to throttling To matchwith the high backpressure a shock train in the isolator isformed Then the augment of the backpressure leads to thatthe shock train moves upstream At about 05ms the shocktrain leading edge is pushed to the inlet throat The coreflow which contains shock train moves downstream whileboundary layers shift upstream The flowfiled structures ofmodule I and module III however are distinct with that ofmodule II And no high backpressure no shock train and no

6 The Scientific World Journal

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 6 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

reversed flow are formed since there is no throttling at theirexits

Stage II Shock System Disgorging (05sim20ms) In module IIthe shock train is expelled from isolator when backpressureincreases to some extents leading to that the external shocksystemmoves upstream and the capturedmassflow descendsThe gradual increase of adverse pressure gradient results inthat the reversed flow occupies more and more part of theinternal flowfield until all flow is reversed and the velocityof reversed flow also increases gradually In addition theentrance part of inlet acts as a diverging duct for the reversedflow and thus the velocity of the reversed flow increasesfurther However no reversed flow emerges in the isolatorof module I and module III while the flow velocity reducesfrom supersonic to subsonic only a part of airflow enters theisolator due the spillage It is worth to note that module Iand module III are both unstarted and their external shocksystems are the same with that of module II though theirinternal flowfield structures are distinct

Stage III Shock System Swallowing (20sim40ms) Most ofairflow spills at stage II Then due to the imbalance betweenless captured mass flow and nearly unchanged dischargedmass flow a pressure trough is formed in the exit andpropagates upstream leading to that the shock systemmovesdownstream At this stage the reversed flow in the isolatorof module II occupies less gradually However there is nochange of flow direction in the isolator of module I andmodule III meanwhile flow velocity increases from subsonicto supersonic Although their internal flowfield structures are

distinct their external shock systems are the same and movedownstream together

Stage IV Duct Pressure Recovering (40sim45ms) The shocksystems reestablish but the pressure of duct is still lower thanthat at 119905 = 0ms With the captured airflow increasing thepressure ascends gradually At about 119905 = 45ms there isa local separated region at the exit of the isolator whichindicates that the pressure recovers that at 119905 = 0msThen thenext buzz cycle begins

According to the analysis of the four stages the unstartmechanism can be discussed simply The occurrence ofunstart is caused by the mass flow rate imbalance betweeninlet entrance and isolator exit The freestream conditionsand the conditions of isolator exit are fixed The flowfieldhowever oscillates all the time In buzz process the spillagechanges and plays an important role Thus the spillage is themajor disturbance source for hypersonic inlets which is alsoproposed by Tan et al [13] based on experimental results

The histories of mass-captured coefficient and staticpressure at the exit of isolator are given in Figure 5 As canbe seen from Figure 5 the buzz characteristic of module Iis the same with that of module III The dominant buzzfrequencies of three modules are 2213Hz indicating thattheir unstarted processes are synchronous The pressureamplitude of module II is higher than that of module I ormodule III and the mass flow rate amplitude of moduleII is lower since the throttling restricts it Thus unstartphenomenon of module II is much stronger

To understand the couple mechanism of unstarted flowfor the multiple-modules hypersonic inlet the flowfield

The Scientific World Journal 7

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

00 ms

(c)

05 ms

02 03 04 05 06

01

(d)

05 ms

02 03 04 05 06

01

(e)

02 03 04 05 06

01

05 ms

(f)

20 ms

02 03 04 05 06

01

(g)

20 ms

02 03 04 05 06

01

(h)

02 03 04 05 06

01

20 ms

(i)

40 ms

00 ms02 03 04 05 06

01

(j)

40 ms

00 ms02 03 04 05 06

01

(k)

02 03 04 05 06

01

40 ms

(l)

45 ms

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

01

(m)

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

0145 ms

(n)

02 03 04 05 06

05 10Mach number20 3015 25 35 4540

01

45 ms

(o)

Figure 7 Mach contours mixing with cross section 1198851 1198852 and 1198853 in a buzz cycle

structure of separated bubble in a buzz cycle was analyzedThe pressure contours with streamlines of cross section Y ina buzz cycle are shown in Figure 6

It can be noted that reversed streamlines emerge inentrance of all modules as shown in Figure 6(a)The reversedstreamlines are located in the initial separated bubble whichhave no influence on analysis of coupling mechanism sincethere is no transverse flow among modules In cross sectionY the intersection line of streamlines where airflow spillsbetween freestream and reversed flow is termed as spilledline in this paper Since reversed flow emerges in module IItwo weak vortexes are formed becoming stronger graduallywith an increase of reversed flow velocity as shown inFigures 6(b) and 6(c)When the reversed flow velocity is highenough spilled line is pushed upstream further and extendsto both sides leading to that the two side vortexes are in

the downstream of spilled line as shown in Figure 6(d) It isworth to note that a small part flow of vortexes enters sidemodules The increase of reversed flow velocity and moreairflow of side vortexes entering the side modules due to theupstreammovement of external shock system encourage twovortexes to expand further The middle part of spilled line ispushed upstreamwhile two-sides part is pushed downstreamwhich leads an arc spilled line to be formed as shownin Figure 6(e) Then external shock system starts movingdownstream The occupation proportion of the reversedflow decreases gradually and the reversed flow disappearseventuallyThe endpart of vortexes enters allmodules and thespilled line is dragged downstream as shown in Figure 6(f)When capturedmass flow increases to some extents the initialseparated bubble recovers gradually Thus the reversed flowof initial separated bubble emerges again and its velocity is

8 The Scientific World Journal

0 2 4 6 8 10 12 140

02

04

06

08

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

Module IModule IIModule III

(a) Mass-captured coefficient

0

05

1

15

2

0 2 4 6 8 10 12 14Time (ms)

Module IModule IIModule III

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 8 The histories of mass-captured coefficient and static pressure at the exit of isolator

higher than that of initial state This reversed flow generatestwo-side weak vortexes With the shock system movingdownstream further external shock system is reestablishedand the disturbance of initial separated bubble becomesweaker Thus the two side vortexes is smaller and smalleruntil disappear as shown in Figures 6(g) and 6(h) The initialseparated bubbles in three modules recover entirely at about45ms as shown in Figure 6(i) At this time transverse flowdisappears which indicates that there is no effect among threemodules

32 Unstarted Flowfield Structure Caused by Module IIIThrottling Next the unstarted flowfield structure caused bymodule III throttling was analyzed Figure 7 presents Machnumber contours of cross section 1198851 1198852 and 1198853 in a buzzcycle It is easy to find that unstarted process includes thesame four stages massfilling up (0sim05ms) shock systemdisgorging (05sim20ms) shock system swallowing (20sim40ms) and duct pressure recovering (40sim45ms)

Similarly the internal flowfield structures among differ-ent modules are distinct There is shock train formation andreversed flow appearance in the isolator of module III whilethese phenomena do not occur in module I and moduleII Their external shock systems are identical and are notdisturbed by internal flowfield

To understand the buzz differences among three mod-ules further the histories of mass-captured coefficient andstatic pressure at the exit are plotted in Figure 8 It iseasy to draw a conclusion that buzz processes of threemodules are synchronous and the dominant frequency is2289Hz while unstart phenomenon of module III is muchstronger

To understand how the unstarted flow of module IIIresults in unstart occurrences in module I and module II the

pressure contours mixing with streamlines of cross section 119884are analyzed and are presented in Figure 9

Similarly three modules do not affect each other sincethere is no transverse flow among modules at the beginningas shown in Figure 9(a) When the shock train arrives at thethroat upstream reversed flow emerges inmodule III leadingto that only one weak vortex is formed by the interactionbetween reversed flow and freestream With the externalshock system moving upstream the augment of adversepressure gradient caused by increasing spillage accelerates thereversed flowThus the vortex becomes bigger and the spilledline is pushed upstream as shown in Figures 9(b) and 9(c)When the vortex expands to some extent freestream ischocked which leads to that a new vortex located upstreamofspilled line is formedHereafter the adverse pressure gradientincreases slowly since duct pressure is low resulting in thatthe velocity of reversed flow increases slowly and more andmore airflow enters module I and module II In additionfreestream is accelerated in the aerodynamics throat which isformed between the two vortexes Thus the upstream vortexexpands with the external shock system moving upstreamfurther while the downstream vortex shrinks as shown inFigures 9(d) and 9(e) Then external shock system startsmoving downstream due to the formation of pressure troughin module III The velocity of reversed flow descends withexternal shock system moving downstream leading to thatthe downstream vortex shrinks gradually and disappearseventually as shown in Figure 9(f) At the same time thechocking effect also decreases gradually due to the shrink-age and the eventual disappearance of downstream vortexleading the upstream vortex to shrink and vanish Then anew and weak vortex is formed by the interaction betweenreversed flow and freestream as shown in Figure 9(g)The initial separated bubble recovers and reversed flowin the isolator of module III disappears gradually with

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

2 The Scientific World Journal

30 15 0minus15 0 50 100 150 200 250 300 350 400 450 500 550 600

X (mm)

Z (mm)

Y(m

m)

120100

80604020

Cross-sectionY

Cross-section Z3

Module III Module IModule II

(a)

L1 L2 L3 L4

L

H

5

L6

1205751

1205752

1205753

1205754

1205755

(b)

Figure 1 The 3D view of multiple-modules hypersonic inlet and geometric parameters

The modular nature facilitates engine scaling An enginecan be easily scaled by adding more flowpaths withoutrequiring fueling redistribution because each flowpath isidentical In addition scaling in this manner does not changethe boundary-layer characteristics relative to the flowpathgeometry Aerojet conducted this multiple-modules strutjetengine [14] in this parallel manner The advantage of usingthis approach is that each module is independent and thegeometry and flowfield of scramjet engine are not needed tobe redesigned and it is beneficial to the rapid prototyping ofscramjet engine

Formultiple-modules engines when inlet unstart appearsin a single-module engine due to high backpressure howto interact with each module by the massflow spillage andwhether inlet unstart phenomenon occurs in other modulesare important issues and they are also the investigationemphasis of this paper To discuss this problem inlet modeland numerical method are given in Section 2 Section 3 pre-sents some typical simulation results and analysis Section 4presents some conclusions

2 Inlet Model and Numerical Method

21 Inlet Model The 3D view of a multiple-modules hyper-sonic inlet is presented in Figure 1 The duct of the multiple-modules hypersonic inlet is separated into three modulesmodule I module II and module III

Table 1 Geometric parameters of the hypersonic inlet

1198711m 119871

2m 119871

3m 119871

4m 119871

5m 119871

6m

0212 0113 0106 0169 0144 0048Hm 120575

1∘ 120575

2∘ 120575

3∘ 120575

4∘ 120575

5∘

0015 6 83 98 13 141

The multiple-modules hypersonic inlet is designed asa mixed-compression type including three external shocksand two internal shocks The main geometric parametersof the hypersonic inlet are referred to Figure 1 and Table 1and the length unit is m and the angle unit is degree Thedeflection angle of the three external ramps is 6∘ 83∘and98∘ respectively and the deflection angle of the internal rampand cowl tip is 10∘ and 141∘ respectively These compressionramps can guarantee the formation of a set of similar strengthshock The external contraction ratio and internal one are547 and 129 so the total one is 705

To show and analyze the flowfield structure convenientlyin Section 3 some typical cross-sections are defined Cross-section 1198851 cross section 1198852 and cross section 1198853 parallel to119883119884 plane and their values of119885-axis areminus75mm 75mm and225mm respectively Cross section119884parallels119883119885plane justlocated at the inlet entrance These typical cross sections will

The Scientific World Journal 3

(a) Simulation results (Mach number contour) (b) Experimental results

Figure 2 Comparison between Mach number contour and Schlieren pictures of a started inlet

t = 0ms

t = 1ms

t = 2ms

t = 3ms

t = 4ms

t = 5ms

(a) Simulation results (Mach number contour)

t998400= 5ms

t998400= 0ms

t998400= 1ms

t998400= 2ms

t998400= 3ms

Slipping layer

t998400= 4ms

t998400= 5ms

(b) Experimental results

Figure 3 Comparison between Mach number contour and Schlieren pictures in a big buzz cycle

be used to analyze the unstart coupling mechanism of themultiple-modules hypersonic inlet

22 Numerical Method The computation is performedusing the finite-volume technique with upwind discretiza-tion to solve the three-dimensional compressible Reynolds-Averaged Navier-Stokes equations The fluid was modeledas a single-specie thermally perfect air The piecewise-polynomial method was selected to compute specific heatwhile viscosity was solved using Sutherlandrsquos formulaThe space discretization is performed by a cell-centered for-mulationThe advection upstream splitting method (AUSM)flux vector splitting is applied for the approximation ofthe convective flux functions Higher-order accuracy forthe upwind discretization and consistency with the centraldifferences used for the diffusive term is achieved by the

monotonic upstream scheme for conservation laws extrap-olations and the total variation diminishing property of thescheme is ensured by the Van Leer flux limiter For transientsimulations the governing equations must be discretized inboth space and time Temporal discretization involves theintegration of every term in the differential equations over atime step Time integration is performed by an implicit fivestage Runge-Kutta time-stepping scheme in the computationand the advantage of the fully implicit scheme is that it isunconditionally stable with respect to time step size

The computations have been performed using a struc-tured grid An excellent quality all-quad 3D mesh with2000 k control volumes is generated for the simulation andensuring the maximum 119910+ was below 10 required for usingwith Shear-Stress Transport (SST) turbulence mode whichis found to be the feasible turbulence model option for

4 The Scientific World Journal

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

05 ms

(c)

01

02 03 04 05 06

05 ms

(d)

01

02 03 04 05 06

20 ms

(e)

01

02 03 04 05 06

20 ms

(f)

01

02 03 04 05 06

40 ms

(g)

01

02 03 04 05 06

40 ms

(h)

01

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

45 ms

(i)

01

02 03 04 05 06

45 ms

05 10Mach number

20 3015 25 35 4540

(j)

Figure 4 Mach contours mixing with streamlines of cross section 1198851 (1198853) and 1198852 in a buzz cycle

the simulation of vortices embedded in a boundary layerFor the steady simulation the mass conservation is checkedby measuring the mass-flow rate error In general 05 erroris a good indicator for convergence

The boundary condition of the supersonic inflow is far-pressure field and the freestream conditions can be defined

by specifying the boundary conditions The boundary con-dition of the exit of the isolator is the pressure outlet andthe backpressure can be defined by changing the throttlingarea shown in Figure 1 At solid walls the no-slip boundarycondition is enforced by setting the velocity components tozero

The Scientific World Journal 5

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

0 2 4 6 8 10 12 140

01

02

03

04

05

06

07

Module IModule IIModule III

(a) Mass-captured coefficient

Module IModule IIModule III

0 2 4 6 8 10 12 140

05

1

15

2

25

Time (ms)

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 5 The histories of mass-captured coefficient and static pressure at the exit of isolator

23 Numerical Accuracy Analysis Firstly comparison of aSchlieren picture [13] without throttling and correspondingMach number contour lines of the computation is shown inFigure 2 and it reveals an overall good agreementThe shockwave pattern the separation and the approximate boundary-layer thickness of the Schlieren picture are also present inthe simulation results Secondly comparison of a Schlierenpicture [13] with higher throttling ratio and correspondingMach number contour lines of the computation is shown inFigure 3 At a higher throttling ratio the hypersonic inletbuzz appears It can be seen that during a big buzz cyclethe inlet flow patterns exhibit a series of striking changes incontrast with a little buzz The external compression shocksystem is first destroyed and then reestablished the entranceseparation bubble is first disgorged and then swallowed andthe shock train in the isolator is first developed and thendispelled

As discussed above the comparison between the sim-ulation and experimental results shows that the simulationresults accord with the physical conception of the aerody-namics and can reveal the primary characteristics of startedand unstarted hypersonic inlet

3 Results and Discussion

Whether inlet unstart phenomenon occurs or not dependson the mass flow rate balance between inlet entrance andcombustor exit If Mach number of the freestream is loweror the combustor backpressure is higher inlet unstart wouldappear For the multiple-modules hypersonic inlet on theone hand the difference of forebody shock compression ofeach module hypersonic inlet and the variation of angleof attacksideslip angle all lead to the nonuniform of the

flowfield at the entrance of isolators on the other hand thecombustion oscillation or deflagration all result in that thepressure at the exit of isolators shows uneven In contrast witha single-module engine the factors discussed above increasethe matching difficulty between the inlet and combustorcharacteristics for multiple-modules scramjet engines Theemphasis of this paper is to investigate the unstart couplingmechanism of multiple-modules hypersonic inlet due to thebackpressure of a single-module hypersonic inlet especiallyon how to interact with eachmodule by themassflow spillage

31 Unstarted Flowfield Structure Caused by Module II Throt-tling Firstly the unstarted flowfield structure caused bymodule II throttling was investigated Because the contour ofcross section 1198851 is the same as that of cross section 1198853 onlyone of them is presented Mach number contours of crosssection 1198851 and 1198852 in a buzz cycle are shown in Figure 4

As can be seen from the figure of 119905 = 0ms in Figure 4inlet is started though a small separated bubble is formed inentranceThe separated bubble is termed as ldquoinitial separatedbubblerdquo in order to facilitate the description below Theflowfield structure of the multiple-modules hypersonic inletgoes through four stages as follows

Stage I MassFilling Up (0sim05ms) A high pressure region isformed at the exit of module II due to throttling To matchwith the high backpressure a shock train in the isolator isformed Then the augment of the backpressure leads to thatthe shock train moves upstream At about 05ms the shocktrain leading edge is pushed to the inlet throat The coreflow which contains shock train moves downstream whileboundary layers shift upstream The flowfiled structures ofmodule I and module III however are distinct with that ofmodule II And no high backpressure no shock train and no

6 The Scientific World Journal

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 6 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

reversed flow are formed since there is no throttling at theirexits

Stage II Shock System Disgorging (05sim20ms) In module IIthe shock train is expelled from isolator when backpressureincreases to some extents leading to that the external shocksystemmoves upstream and the capturedmassflow descendsThe gradual increase of adverse pressure gradient results inthat the reversed flow occupies more and more part of theinternal flowfield until all flow is reversed and the velocityof reversed flow also increases gradually In addition theentrance part of inlet acts as a diverging duct for the reversedflow and thus the velocity of the reversed flow increasesfurther However no reversed flow emerges in the isolatorof module I and module III while the flow velocity reducesfrom supersonic to subsonic only a part of airflow enters theisolator due the spillage It is worth to note that module Iand module III are both unstarted and their external shocksystems are the same with that of module II though theirinternal flowfield structures are distinct

Stage III Shock System Swallowing (20sim40ms) Most ofairflow spills at stage II Then due to the imbalance betweenless captured mass flow and nearly unchanged dischargedmass flow a pressure trough is formed in the exit andpropagates upstream leading to that the shock systemmovesdownstream At this stage the reversed flow in the isolatorof module II occupies less gradually However there is nochange of flow direction in the isolator of module I andmodule III meanwhile flow velocity increases from subsonicto supersonic Although their internal flowfield structures are

distinct their external shock systems are the same and movedownstream together

Stage IV Duct Pressure Recovering (40sim45ms) The shocksystems reestablish but the pressure of duct is still lower thanthat at 119905 = 0ms With the captured airflow increasing thepressure ascends gradually At about 119905 = 45ms there isa local separated region at the exit of the isolator whichindicates that the pressure recovers that at 119905 = 0msThen thenext buzz cycle begins

According to the analysis of the four stages the unstartmechanism can be discussed simply The occurrence ofunstart is caused by the mass flow rate imbalance betweeninlet entrance and isolator exit The freestream conditionsand the conditions of isolator exit are fixed The flowfieldhowever oscillates all the time In buzz process the spillagechanges and plays an important role Thus the spillage is themajor disturbance source for hypersonic inlets which is alsoproposed by Tan et al [13] based on experimental results

The histories of mass-captured coefficient and staticpressure at the exit of isolator are given in Figure 5 As canbe seen from Figure 5 the buzz characteristic of module Iis the same with that of module III The dominant buzzfrequencies of three modules are 2213Hz indicating thattheir unstarted processes are synchronous The pressureamplitude of module II is higher than that of module I ormodule III and the mass flow rate amplitude of moduleII is lower since the throttling restricts it Thus unstartphenomenon of module II is much stronger

To understand the couple mechanism of unstarted flowfor the multiple-modules hypersonic inlet the flowfield

The Scientific World Journal 7

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

00 ms

(c)

05 ms

02 03 04 05 06

01

(d)

05 ms

02 03 04 05 06

01

(e)

02 03 04 05 06

01

05 ms

(f)

20 ms

02 03 04 05 06

01

(g)

20 ms

02 03 04 05 06

01

(h)

02 03 04 05 06

01

20 ms

(i)

40 ms

00 ms02 03 04 05 06

01

(j)

40 ms

00 ms02 03 04 05 06

01

(k)

02 03 04 05 06

01

40 ms

(l)

45 ms

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

01

(m)

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

0145 ms

(n)

02 03 04 05 06

05 10Mach number20 3015 25 35 4540

01

45 ms

(o)

Figure 7 Mach contours mixing with cross section 1198851 1198852 and 1198853 in a buzz cycle

structure of separated bubble in a buzz cycle was analyzedThe pressure contours with streamlines of cross section Y ina buzz cycle are shown in Figure 6

It can be noted that reversed streamlines emerge inentrance of all modules as shown in Figure 6(a)The reversedstreamlines are located in the initial separated bubble whichhave no influence on analysis of coupling mechanism sincethere is no transverse flow among modules In cross sectionY the intersection line of streamlines where airflow spillsbetween freestream and reversed flow is termed as spilledline in this paper Since reversed flow emerges in module IItwo weak vortexes are formed becoming stronger graduallywith an increase of reversed flow velocity as shown inFigures 6(b) and 6(c)When the reversed flow velocity is highenough spilled line is pushed upstream further and extendsto both sides leading to that the two side vortexes are in

the downstream of spilled line as shown in Figure 6(d) It isworth to note that a small part flow of vortexes enters sidemodules The increase of reversed flow velocity and moreairflow of side vortexes entering the side modules due to theupstreammovement of external shock system encourage twovortexes to expand further The middle part of spilled line ispushed upstreamwhile two-sides part is pushed downstreamwhich leads an arc spilled line to be formed as shownin Figure 6(e) Then external shock system starts movingdownstream The occupation proportion of the reversedflow decreases gradually and the reversed flow disappearseventuallyThe endpart of vortexes enters allmodules and thespilled line is dragged downstream as shown in Figure 6(f)When capturedmass flow increases to some extents the initialseparated bubble recovers gradually Thus the reversed flowof initial separated bubble emerges again and its velocity is

8 The Scientific World Journal

0 2 4 6 8 10 12 140

02

04

06

08

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

Module IModule IIModule III

(a) Mass-captured coefficient

0

05

1

15

2

0 2 4 6 8 10 12 14Time (ms)

Module IModule IIModule III

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 8 The histories of mass-captured coefficient and static pressure at the exit of isolator

higher than that of initial state This reversed flow generatestwo-side weak vortexes With the shock system movingdownstream further external shock system is reestablishedand the disturbance of initial separated bubble becomesweaker Thus the two side vortexes is smaller and smalleruntil disappear as shown in Figures 6(g) and 6(h) The initialseparated bubbles in three modules recover entirely at about45ms as shown in Figure 6(i) At this time transverse flowdisappears which indicates that there is no effect among threemodules

32 Unstarted Flowfield Structure Caused by Module IIIThrottling Next the unstarted flowfield structure caused bymodule III throttling was analyzed Figure 7 presents Machnumber contours of cross section 1198851 1198852 and 1198853 in a buzzcycle It is easy to find that unstarted process includes thesame four stages massfilling up (0sim05ms) shock systemdisgorging (05sim20ms) shock system swallowing (20sim40ms) and duct pressure recovering (40sim45ms)

Similarly the internal flowfield structures among differ-ent modules are distinct There is shock train formation andreversed flow appearance in the isolator of module III whilethese phenomena do not occur in module I and moduleII Their external shock systems are identical and are notdisturbed by internal flowfield

To understand the buzz differences among three mod-ules further the histories of mass-captured coefficient andstatic pressure at the exit are plotted in Figure 8 It iseasy to draw a conclusion that buzz processes of threemodules are synchronous and the dominant frequency is2289Hz while unstart phenomenon of module III is muchstronger

To understand how the unstarted flow of module IIIresults in unstart occurrences in module I and module II the

pressure contours mixing with streamlines of cross section 119884are analyzed and are presented in Figure 9

Similarly three modules do not affect each other sincethere is no transverse flow among modules at the beginningas shown in Figure 9(a) When the shock train arrives at thethroat upstream reversed flow emerges inmodule III leadingto that only one weak vortex is formed by the interactionbetween reversed flow and freestream With the externalshock system moving upstream the augment of adversepressure gradient caused by increasing spillage accelerates thereversed flowThus the vortex becomes bigger and the spilledline is pushed upstream as shown in Figures 9(b) and 9(c)When the vortex expands to some extent freestream ischocked which leads to that a new vortex located upstreamofspilled line is formedHereafter the adverse pressure gradientincreases slowly since duct pressure is low resulting in thatthe velocity of reversed flow increases slowly and more andmore airflow enters module I and module II In additionfreestream is accelerated in the aerodynamics throat which isformed between the two vortexes Thus the upstream vortexexpands with the external shock system moving upstreamfurther while the downstream vortex shrinks as shown inFigures 9(d) and 9(e) Then external shock system startsmoving downstream due to the formation of pressure troughin module III The velocity of reversed flow descends withexternal shock system moving downstream leading to thatthe downstream vortex shrinks gradually and disappearseventually as shown in Figure 9(f) At the same time thechocking effect also decreases gradually due to the shrink-age and the eventual disappearance of downstream vortexleading the upstream vortex to shrink and vanish Then anew and weak vortex is formed by the interaction betweenreversed flow and freestream as shown in Figure 9(g)The initial separated bubble recovers and reversed flowin the isolator of module III disappears gradually with

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

The Scientific World Journal 3

(a) Simulation results (Mach number contour) (b) Experimental results

Figure 2 Comparison between Mach number contour and Schlieren pictures of a started inlet

t = 0ms

t = 1ms

t = 2ms

t = 3ms

t = 4ms

t = 5ms

(a) Simulation results (Mach number contour)

t998400= 5ms

t998400= 0ms

t998400= 1ms

t998400= 2ms

t998400= 3ms

Slipping layer

t998400= 4ms

t998400= 5ms

(b) Experimental results

Figure 3 Comparison between Mach number contour and Schlieren pictures in a big buzz cycle

be used to analyze the unstart coupling mechanism of themultiple-modules hypersonic inlet

22 Numerical Method The computation is performedusing the finite-volume technique with upwind discretiza-tion to solve the three-dimensional compressible Reynolds-Averaged Navier-Stokes equations The fluid was modeledas a single-specie thermally perfect air The piecewise-polynomial method was selected to compute specific heatwhile viscosity was solved using Sutherlandrsquos formulaThe space discretization is performed by a cell-centered for-mulationThe advection upstream splitting method (AUSM)flux vector splitting is applied for the approximation ofthe convective flux functions Higher-order accuracy forthe upwind discretization and consistency with the centraldifferences used for the diffusive term is achieved by the

monotonic upstream scheme for conservation laws extrap-olations and the total variation diminishing property of thescheme is ensured by the Van Leer flux limiter For transientsimulations the governing equations must be discretized inboth space and time Temporal discretization involves theintegration of every term in the differential equations over atime step Time integration is performed by an implicit fivestage Runge-Kutta time-stepping scheme in the computationand the advantage of the fully implicit scheme is that it isunconditionally stable with respect to time step size

The computations have been performed using a struc-tured grid An excellent quality all-quad 3D mesh with2000 k control volumes is generated for the simulation andensuring the maximum 119910+ was below 10 required for usingwith Shear-Stress Transport (SST) turbulence mode whichis found to be the feasible turbulence model option for

4 The Scientific World Journal

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

05 ms

(c)

01

02 03 04 05 06

05 ms

(d)

01

02 03 04 05 06

20 ms

(e)

01

02 03 04 05 06

20 ms

(f)

01

02 03 04 05 06

40 ms

(g)

01

02 03 04 05 06

40 ms

(h)

01

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

45 ms

(i)

01

02 03 04 05 06

45 ms

05 10Mach number

20 3015 25 35 4540

(j)

Figure 4 Mach contours mixing with streamlines of cross section 1198851 (1198853) and 1198852 in a buzz cycle

the simulation of vortices embedded in a boundary layerFor the steady simulation the mass conservation is checkedby measuring the mass-flow rate error In general 05 erroris a good indicator for convergence

The boundary condition of the supersonic inflow is far-pressure field and the freestream conditions can be defined

by specifying the boundary conditions The boundary con-dition of the exit of the isolator is the pressure outlet andthe backpressure can be defined by changing the throttlingarea shown in Figure 1 At solid walls the no-slip boundarycondition is enforced by setting the velocity components tozero

The Scientific World Journal 5

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

0 2 4 6 8 10 12 140

01

02

03

04

05

06

07

Module IModule IIModule III

(a) Mass-captured coefficient

Module IModule IIModule III

0 2 4 6 8 10 12 140

05

1

15

2

25

Time (ms)

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 5 The histories of mass-captured coefficient and static pressure at the exit of isolator

23 Numerical Accuracy Analysis Firstly comparison of aSchlieren picture [13] without throttling and correspondingMach number contour lines of the computation is shown inFigure 2 and it reveals an overall good agreementThe shockwave pattern the separation and the approximate boundary-layer thickness of the Schlieren picture are also present inthe simulation results Secondly comparison of a Schlierenpicture [13] with higher throttling ratio and correspondingMach number contour lines of the computation is shown inFigure 3 At a higher throttling ratio the hypersonic inletbuzz appears It can be seen that during a big buzz cyclethe inlet flow patterns exhibit a series of striking changes incontrast with a little buzz The external compression shocksystem is first destroyed and then reestablished the entranceseparation bubble is first disgorged and then swallowed andthe shock train in the isolator is first developed and thendispelled

As discussed above the comparison between the sim-ulation and experimental results shows that the simulationresults accord with the physical conception of the aerody-namics and can reveal the primary characteristics of startedand unstarted hypersonic inlet

3 Results and Discussion

Whether inlet unstart phenomenon occurs or not dependson the mass flow rate balance between inlet entrance andcombustor exit If Mach number of the freestream is loweror the combustor backpressure is higher inlet unstart wouldappear For the multiple-modules hypersonic inlet on theone hand the difference of forebody shock compression ofeach module hypersonic inlet and the variation of angleof attacksideslip angle all lead to the nonuniform of the

flowfield at the entrance of isolators on the other hand thecombustion oscillation or deflagration all result in that thepressure at the exit of isolators shows uneven In contrast witha single-module engine the factors discussed above increasethe matching difficulty between the inlet and combustorcharacteristics for multiple-modules scramjet engines Theemphasis of this paper is to investigate the unstart couplingmechanism of multiple-modules hypersonic inlet due to thebackpressure of a single-module hypersonic inlet especiallyon how to interact with eachmodule by themassflow spillage

31 Unstarted Flowfield Structure Caused by Module II Throt-tling Firstly the unstarted flowfield structure caused bymodule II throttling was investigated Because the contour ofcross section 1198851 is the same as that of cross section 1198853 onlyone of them is presented Mach number contours of crosssection 1198851 and 1198852 in a buzz cycle are shown in Figure 4

As can be seen from the figure of 119905 = 0ms in Figure 4inlet is started though a small separated bubble is formed inentranceThe separated bubble is termed as ldquoinitial separatedbubblerdquo in order to facilitate the description below Theflowfield structure of the multiple-modules hypersonic inletgoes through four stages as follows

Stage I MassFilling Up (0sim05ms) A high pressure region isformed at the exit of module II due to throttling To matchwith the high backpressure a shock train in the isolator isformed Then the augment of the backpressure leads to thatthe shock train moves upstream At about 05ms the shocktrain leading edge is pushed to the inlet throat The coreflow which contains shock train moves downstream whileboundary layers shift upstream The flowfiled structures ofmodule I and module III however are distinct with that ofmodule II And no high backpressure no shock train and no

6 The Scientific World Journal

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 6 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

reversed flow are formed since there is no throttling at theirexits

Stage II Shock System Disgorging (05sim20ms) In module IIthe shock train is expelled from isolator when backpressureincreases to some extents leading to that the external shocksystemmoves upstream and the capturedmassflow descendsThe gradual increase of adverse pressure gradient results inthat the reversed flow occupies more and more part of theinternal flowfield until all flow is reversed and the velocityof reversed flow also increases gradually In addition theentrance part of inlet acts as a diverging duct for the reversedflow and thus the velocity of the reversed flow increasesfurther However no reversed flow emerges in the isolatorof module I and module III while the flow velocity reducesfrom supersonic to subsonic only a part of airflow enters theisolator due the spillage It is worth to note that module Iand module III are both unstarted and their external shocksystems are the same with that of module II though theirinternal flowfield structures are distinct

Stage III Shock System Swallowing (20sim40ms) Most ofairflow spills at stage II Then due to the imbalance betweenless captured mass flow and nearly unchanged dischargedmass flow a pressure trough is formed in the exit andpropagates upstream leading to that the shock systemmovesdownstream At this stage the reversed flow in the isolatorof module II occupies less gradually However there is nochange of flow direction in the isolator of module I andmodule III meanwhile flow velocity increases from subsonicto supersonic Although their internal flowfield structures are

distinct their external shock systems are the same and movedownstream together

Stage IV Duct Pressure Recovering (40sim45ms) The shocksystems reestablish but the pressure of duct is still lower thanthat at 119905 = 0ms With the captured airflow increasing thepressure ascends gradually At about 119905 = 45ms there isa local separated region at the exit of the isolator whichindicates that the pressure recovers that at 119905 = 0msThen thenext buzz cycle begins

According to the analysis of the four stages the unstartmechanism can be discussed simply The occurrence ofunstart is caused by the mass flow rate imbalance betweeninlet entrance and isolator exit The freestream conditionsand the conditions of isolator exit are fixed The flowfieldhowever oscillates all the time In buzz process the spillagechanges and plays an important role Thus the spillage is themajor disturbance source for hypersonic inlets which is alsoproposed by Tan et al [13] based on experimental results

The histories of mass-captured coefficient and staticpressure at the exit of isolator are given in Figure 5 As canbe seen from Figure 5 the buzz characteristic of module Iis the same with that of module III The dominant buzzfrequencies of three modules are 2213Hz indicating thattheir unstarted processes are synchronous The pressureamplitude of module II is higher than that of module I ormodule III and the mass flow rate amplitude of moduleII is lower since the throttling restricts it Thus unstartphenomenon of module II is much stronger

To understand the couple mechanism of unstarted flowfor the multiple-modules hypersonic inlet the flowfield

The Scientific World Journal 7

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

00 ms

(c)

05 ms

02 03 04 05 06

01

(d)

05 ms

02 03 04 05 06

01

(e)

02 03 04 05 06

01

05 ms

(f)

20 ms

02 03 04 05 06

01

(g)

20 ms

02 03 04 05 06

01

(h)

02 03 04 05 06

01

20 ms

(i)

40 ms

00 ms02 03 04 05 06

01

(j)

40 ms

00 ms02 03 04 05 06

01

(k)

02 03 04 05 06

01

40 ms

(l)

45 ms

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

01

(m)

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

0145 ms

(n)

02 03 04 05 06

05 10Mach number20 3015 25 35 4540

01

45 ms

(o)

Figure 7 Mach contours mixing with cross section 1198851 1198852 and 1198853 in a buzz cycle

structure of separated bubble in a buzz cycle was analyzedThe pressure contours with streamlines of cross section Y ina buzz cycle are shown in Figure 6

It can be noted that reversed streamlines emerge inentrance of all modules as shown in Figure 6(a)The reversedstreamlines are located in the initial separated bubble whichhave no influence on analysis of coupling mechanism sincethere is no transverse flow among modules In cross sectionY the intersection line of streamlines where airflow spillsbetween freestream and reversed flow is termed as spilledline in this paper Since reversed flow emerges in module IItwo weak vortexes are formed becoming stronger graduallywith an increase of reversed flow velocity as shown inFigures 6(b) and 6(c)When the reversed flow velocity is highenough spilled line is pushed upstream further and extendsto both sides leading to that the two side vortexes are in

the downstream of spilled line as shown in Figure 6(d) It isworth to note that a small part flow of vortexes enters sidemodules The increase of reversed flow velocity and moreairflow of side vortexes entering the side modules due to theupstreammovement of external shock system encourage twovortexes to expand further The middle part of spilled line ispushed upstreamwhile two-sides part is pushed downstreamwhich leads an arc spilled line to be formed as shownin Figure 6(e) Then external shock system starts movingdownstream The occupation proportion of the reversedflow decreases gradually and the reversed flow disappearseventuallyThe endpart of vortexes enters allmodules and thespilled line is dragged downstream as shown in Figure 6(f)When capturedmass flow increases to some extents the initialseparated bubble recovers gradually Thus the reversed flowof initial separated bubble emerges again and its velocity is

8 The Scientific World Journal

0 2 4 6 8 10 12 140

02

04

06

08

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

Module IModule IIModule III

(a) Mass-captured coefficient

0

05

1

15

2

0 2 4 6 8 10 12 14Time (ms)

Module IModule IIModule III

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 8 The histories of mass-captured coefficient and static pressure at the exit of isolator

higher than that of initial state This reversed flow generatestwo-side weak vortexes With the shock system movingdownstream further external shock system is reestablishedand the disturbance of initial separated bubble becomesweaker Thus the two side vortexes is smaller and smalleruntil disappear as shown in Figures 6(g) and 6(h) The initialseparated bubbles in three modules recover entirely at about45ms as shown in Figure 6(i) At this time transverse flowdisappears which indicates that there is no effect among threemodules

32 Unstarted Flowfield Structure Caused by Module IIIThrottling Next the unstarted flowfield structure caused bymodule III throttling was analyzed Figure 7 presents Machnumber contours of cross section 1198851 1198852 and 1198853 in a buzzcycle It is easy to find that unstarted process includes thesame four stages massfilling up (0sim05ms) shock systemdisgorging (05sim20ms) shock system swallowing (20sim40ms) and duct pressure recovering (40sim45ms)

Similarly the internal flowfield structures among differ-ent modules are distinct There is shock train formation andreversed flow appearance in the isolator of module III whilethese phenomena do not occur in module I and moduleII Their external shock systems are identical and are notdisturbed by internal flowfield

To understand the buzz differences among three mod-ules further the histories of mass-captured coefficient andstatic pressure at the exit are plotted in Figure 8 It iseasy to draw a conclusion that buzz processes of threemodules are synchronous and the dominant frequency is2289Hz while unstart phenomenon of module III is muchstronger

To understand how the unstarted flow of module IIIresults in unstart occurrences in module I and module II the

pressure contours mixing with streamlines of cross section 119884are analyzed and are presented in Figure 9

Similarly three modules do not affect each other sincethere is no transverse flow among modules at the beginningas shown in Figure 9(a) When the shock train arrives at thethroat upstream reversed flow emerges inmodule III leadingto that only one weak vortex is formed by the interactionbetween reversed flow and freestream With the externalshock system moving upstream the augment of adversepressure gradient caused by increasing spillage accelerates thereversed flowThus the vortex becomes bigger and the spilledline is pushed upstream as shown in Figures 9(b) and 9(c)When the vortex expands to some extent freestream ischocked which leads to that a new vortex located upstreamofspilled line is formedHereafter the adverse pressure gradientincreases slowly since duct pressure is low resulting in thatthe velocity of reversed flow increases slowly and more andmore airflow enters module I and module II In additionfreestream is accelerated in the aerodynamics throat which isformed between the two vortexes Thus the upstream vortexexpands with the external shock system moving upstreamfurther while the downstream vortex shrinks as shown inFigures 9(d) and 9(e) Then external shock system startsmoving downstream due to the formation of pressure troughin module III The velocity of reversed flow descends withexternal shock system moving downstream leading to thatthe downstream vortex shrinks gradually and disappearseventually as shown in Figure 9(f) At the same time thechocking effect also decreases gradually due to the shrink-age and the eventual disappearance of downstream vortexleading the upstream vortex to shrink and vanish Then anew and weak vortex is formed by the interaction betweenreversed flow and freestream as shown in Figure 9(g)The initial separated bubble recovers and reversed flowin the isolator of module III disappears gradually with

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

4 The Scientific World Journal

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

05 ms

(c)

01

02 03 04 05 06

05 ms

(d)

01

02 03 04 05 06

20 ms

(e)

01

02 03 04 05 06

20 ms

(f)

01

02 03 04 05 06

40 ms

(g)

01

02 03 04 05 06

40 ms

(h)

01

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

45 ms

(i)

01

02 03 04 05 06

45 ms

05 10Mach number

20 3015 25 35 4540

(j)

Figure 4 Mach contours mixing with streamlines of cross section 1198851 (1198853) and 1198852 in a buzz cycle

the simulation of vortices embedded in a boundary layerFor the steady simulation the mass conservation is checkedby measuring the mass-flow rate error In general 05 erroris a good indicator for convergence

The boundary condition of the supersonic inflow is far-pressure field and the freestream conditions can be defined

by specifying the boundary conditions The boundary con-dition of the exit of the isolator is the pressure outlet andthe backpressure can be defined by changing the throttlingarea shown in Figure 1 At solid walls the no-slip boundarycondition is enforced by setting the velocity components tozero

The Scientific World Journal 5

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

0 2 4 6 8 10 12 140

01

02

03

04

05

06

07

Module IModule IIModule III

(a) Mass-captured coefficient

Module IModule IIModule III

0 2 4 6 8 10 12 140

05

1

15

2

25

Time (ms)

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 5 The histories of mass-captured coefficient and static pressure at the exit of isolator

23 Numerical Accuracy Analysis Firstly comparison of aSchlieren picture [13] without throttling and correspondingMach number contour lines of the computation is shown inFigure 2 and it reveals an overall good agreementThe shockwave pattern the separation and the approximate boundary-layer thickness of the Schlieren picture are also present inthe simulation results Secondly comparison of a Schlierenpicture [13] with higher throttling ratio and correspondingMach number contour lines of the computation is shown inFigure 3 At a higher throttling ratio the hypersonic inletbuzz appears It can be seen that during a big buzz cyclethe inlet flow patterns exhibit a series of striking changes incontrast with a little buzz The external compression shocksystem is first destroyed and then reestablished the entranceseparation bubble is first disgorged and then swallowed andthe shock train in the isolator is first developed and thendispelled

As discussed above the comparison between the sim-ulation and experimental results shows that the simulationresults accord with the physical conception of the aerody-namics and can reveal the primary characteristics of startedand unstarted hypersonic inlet

3 Results and Discussion

Whether inlet unstart phenomenon occurs or not dependson the mass flow rate balance between inlet entrance andcombustor exit If Mach number of the freestream is loweror the combustor backpressure is higher inlet unstart wouldappear For the multiple-modules hypersonic inlet on theone hand the difference of forebody shock compression ofeach module hypersonic inlet and the variation of angleof attacksideslip angle all lead to the nonuniform of the

flowfield at the entrance of isolators on the other hand thecombustion oscillation or deflagration all result in that thepressure at the exit of isolators shows uneven In contrast witha single-module engine the factors discussed above increasethe matching difficulty between the inlet and combustorcharacteristics for multiple-modules scramjet engines Theemphasis of this paper is to investigate the unstart couplingmechanism of multiple-modules hypersonic inlet due to thebackpressure of a single-module hypersonic inlet especiallyon how to interact with eachmodule by themassflow spillage

31 Unstarted Flowfield Structure Caused by Module II Throt-tling Firstly the unstarted flowfield structure caused bymodule II throttling was investigated Because the contour ofcross section 1198851 is the same as that of cross section 1198853 onlyone of them is presented Mach number contours of crosssection 1198851 and 1198852 in a buzz cycle are shown in Figure 4

As can be seen from the figure of 119905 = 0ms in Figure 4inlet is started though a small separated bubble is formed inentranceThe separated bubble is termed as ldquoinitial separatedbubblerdquo in order to facilitate the description below Theflowfield structure of the multiple-modules hypersonic inletgoes through four stages as follows

Stage I MassFilling Up (0sim05ms) A high pressure region isformed at the exit of module II due to throttling To matchwith the high backpressure a shock train in the isolator isformed Then the augment of the backpressure leads to thatthe shock train moves upstream At about 05ms the shocktrain leading edge is pushed to the inlet throat The coreflow which contains shock train moves downstream whileboundary layers shift upstream The flowfiled structures ofmodule I and module III however are distinct with that ofmodule II And no high backpressure no shock train and no

6 The Scientific World Journal

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 6 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

reversed flow are formed since there is no throttling at theirexits

Stage II Shock System Disgorging (05sim20ms) In module IIthe shock train is expelled from isolator when backpressureincreases to some extents leading to that the external shocksystemmoves upstream and the capturedmassflow descendsThe gradual increase of adverse pressure gradient results inthat the reversed flow occupies more and more part of theinternal flowfield until all flow is reversed and the velocityof reversed flow also increases gradually In addition theentrance part of inlet acts as a diverging duct for the reversedflow and thus the velocity of the reversed flow increasesfurther However no reversed flow emerges in the isolatorof module I and module III while the flow velocity reducesfrom supersonic to subsonic only a part of airflow enters theisolator due the spillage It is worth to note that module Iand module III are both unstarted and their external shocksystems are the same with that of module II though theirinternal flowfield structures are distinct

Stage III Shock System Swallowing (20sim40ms) Most ofairflow spills at stage II Then due to the imbalance betweenless captured mass flow and nearly unchanged dischargedmass flow a pressure trough is formed in the exit andpropagates upstream leading to that the shock systemmovesdownstream At this stage the reversed flow in the isolatorof module II occupies less gradually However there is nochange of flow direction in the isolator of module I andmodule III meanwhile flow velocity increases from subsonicto supersonic Although their internal flowfield structures are

distinct their external shock systems are the same and movedownstream together

Stage IV Duct Pressure Recovering (40sim45ms) The shocksystems reestablish but the pressure of duct is still lower thanthat at 119905 = 0ms With the captured airflow increasing thepressure ascends gradually At about 119905 = 45ms there isa local separated region at the exit of the isolator whichindicates that the pressure recovers that at 119905 = 0msThen thenext buzz cycle begins

According to the analysis of the four stages the unstartmechanism can be discussed simply The occurrence ofunstart is caused by the mass flow rate imbalance betweeninlet entrance and isolator exit The freestream conditionsand the conditions of isolator exit are fixed The flowfieldhowever oscillates all the time In buzz process the spillagechanges and plays an important role Thus the spillage is themajor disturbance source for hypersonic inlets which is alsoproposed by Tan et al [13] based on experimental results

The histories of mass-captured coefficient and staticpressure at the exit of isolator are given in Figure 5 As canbe seen from Figure 5 the buzz characteristic of module Iis the same with that of module III The dominant buzzfrequencies of three modules are 2213Hz indicating thattheir unstarted processes are synchronous The pressureamplitude of module II is higher than that of module I ormodule III and the mass flow rate amplitude of moduleII is lower since the throttling restricts it Thus unstartphenomenon of module II is much stronger

To understand the couple mechanism of unstarted flowfor the multiple-modules hypersonic inlet the flowfield

The Scientific World Journal 7

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

00 ms

(c)

05 ms

02 03 04 05 06

01

(d)

05 ms

02 03 04 05 06

01

(e)

02 03 04 05 06

01

05 ms

(f)

20 ms

02 03 04 05 06

01

(g)

20 ms

02 03 04 05 06

01

(h)

02 03 04 05 06

01

20 ms

(i)

40 ms

00 ms02 03 04 05 06

01

(j)

40 ms

00 ms02 03 04 05 06

01

(k)

02 03 04 05 06

01

40 ms

(l)

45 ms

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

01

(m)

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

0145 ms

(n)

02 03 04 05 06

05 10Mach number20 3015 25 35 4540

01

45 ms

(o)

Figure 7 Mach contours mixing with cross section 1198851 1198852 and 1198853 in a buzz cycle

structure of separated bubble in a buzz cycle was analyzedThe pressure contours with streamlines of cross section Y ina buzz cycle are shown in Figure 6

It can be noted that reversed streamlines emerge inentrance of all modules as shown in Figure 6(a)The reversedstreamlines are located in the initial separated bubble whichhave no influence on analysis of coupling mechanism sincethere is no transverse flow among modules In cross sectionY the intersection line of streamlines where airflow spillsbetween freestream and reversed flow is termed as spilledline in this paper Since reversed flow emerges in module IItwo weak vortexes are formed becoming stronger graduallywith an increase of reversed flow velocity as shown inFigures 6(b) and 6(c)When the reversed flow velocity is highenough spilled line is pushed upstream further and extendsto both sides leading to that the two side vortexes are in

the downstream of spilled line as shown in Figure 6(d) It isworth to note that a small part flow of vortexes enters sidemodules The increase of reversed flow velocity and moreairflow of side vortexes entering the side modules due to theupstreammovement of external shock system encourage twovortexes to expand further The middle part of spilled line ispushed upstreamwhile two-sides part is pushed downstreamwhich leads an arc spilled line to be formed as shownin Figure 6(e) Then external shock system starts movingdownstream The occupation proportion of the reversedflow decreases gradually and the reversed flow disappearseventuallyThe endpart of vortexes enters allmodules and thespilled line is dragged downstream as shown in Figure 6(f)When capturedmass flow increases to some extents the initialseparated bubble recovers gradually Thus the reversed flowof initial separated bubble emerges again and its velocity is

8 The Scientific World Journal

0 2 4 6 8 10 12 140

02

04

06

08

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

Module IModule IIModule III

(a) Mass-captured coefficient

0

05

1

15

2

0 2 4 6 8 10 12 14Time (ms)

Module IModule IIModule III

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 8 The histories of mass-captured coefficient and static pressure at the exit of isolator

higher than that of initial state This reversed flow generatestwo-side weak vortexes With the shock system movingdownstream further external shock system is reestablishedand the disturbance of initial separated bubble becomesweaker Thus the two side vortexes is smaller and smalleruntil disappear as shown in Figures 6(g) and 6(h) The initialseparated bubbles in three modules recover entirely at about45ms as shown in Figure 6(i) At this time transverse flowdisappears which indicates that there is no effect among threemodules

32 Unstarted Flowfield Structure Caused by Module IIIThrottling Next the unstarted flowfield structure caused bymodule III throttling was analyzed Figure 7 presents Machnumber contours of cross section 1198851 1198852 and 1198853 in a buzzcycle It is easy to find that unstarted process includes thesame four stages massfilling up (0sim05ms) shock systemdisgorging (05sim20ms) shock system swallowing (20sim40ms) and duct pressure recovering (40sim45ms)

Similarly the internal flowfield structures among differ-ent modules are distinct There is shock train formation andreversed flow appearance in the isolator of module III whilethese phenomena do not occur in module I and moduleII Their external shock systems are identical and are notdisturbed by internal flowfield

To understand the buzz differences among three mod-ules further the histories of mass-captured coefficient andstatic pressure at the exit are plotted in Figure 8 It iseasy to draw a conclusion that buzz processes of threemodules are synchronous and the dominant frequency is2289Hz while unstart phenomenon of module III is muchstronger

To understand how the unstarted flow of module IIIresults in unstart occurrences in module I and module II the

pressure contours mixing with streamlines of cross section 119884are analyzed and are presented in Figure 9

Similarly three modules do not affect each other sincethere is no transverse flow among modules at the beginningas shown in Figure 9(a) When the shock train arrives at thethroat upstream reversed flow emerges inmodule III leadingto that only one weak vortex is formed by the interactionbetween reversed flow and freestream With the externalshock system moving upstream the augment of adversepressure gradient caused by increasing spillage accelerates thereversed flowThus the vortex becomes bigger and the spilledline is pushed upstream as shown in Figures 9(b) and 9(c)When the vortex expands to some extent freestream ischocked which leads to that a new vortex located upstreamofspilled line is formedHereafter the adverse pressure gradientincreases slowly since duct pressure is low resulting in thatthe velocity of reversed flow increases slowly and more andmore airflow enters module I and module II In additionfreestream is accelerated in the aerodynamics throat which isformed between the two vortexes Thus the upstream vortexexpands with the external shock system moving upstreamfurther while the downstream vortex shrinks as shown inFigures 9(d) and 9(e) Then external shock system startsmoving downstream due to the formation of pressure troughin module III The velocity of reversed flow descends withexternal shock system moving downstream leading to thatthe downstream vortex shrinks gradually and disappearseventually as shown in Figure 9(f) At the same time thechocking effect also decreases gradually due to the shrink-age and the eventual disappearance of downstream vortexleading the upstream vortex to shrink and vanish Then anew and weak vortex is formed by the interaction betweenreversed flow and freestream as shown in Figure 9(g)The initial separated bubble recovers and reversed flowin the isolator of module III disappears gradually with

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

The Scientific World Journal 5

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

0 2 4 6 8 10 12 140

01

02

03

04

05

06

07

Module IModule IIModule III

(a) Mass-captured coefficient

Module IModule IIModule III

0 2 4 6 8 10 12 140

05

1

15

2

25

Time (ms)

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 5 The histories of mass-captured coefficient and static pressure at the exit of isolator

23 Numerical Accuracy Analysis Firstly comparison of aSchlieren picture [13] without throttling and correspondingMach number contour lines of the computation is shown inFigure 2 and it reveals an overall good agreementThe shockwave pattern the separation and the approximate boundary-layer thickness of the Schlieren picture are also present inthe simulation results Secondly comparison of a Schlierenpicture [13] with higher throttling ratio and correspondingMach number contour lines of the computation is shown inFigure 3 At a higher throttling ratio the hypersonic inletbuzz appears It can be seen that during a big buzz cyclethe inlet flow patterns exhibit a series of striking changes incontrast with a little buzz The external compression shocksystem is first destroyed and then reestablished the entranceseparation bubble is first disgorged and then swallowed andthe shock train in the isolator is first developed and thendispelled

As discussed above the comparison between the sim-ulation and experimental results shows that the simulationresults accord with the physical conception of the aerody-namics and can reveal the primary characteristics of startedand unstarted hypersonic inlet

3 Results and Discussion

Whether inlet unstart phenomenon occurs or not dependson the mass flow rate balance between inlet entrance andcombustor exit If Mach number of the freestream is loweror the combustor backpressure is higher inlet unstart wouldappear For the multiple-modules hypersonic inlet on theone hand the difference of forebody shock compression ofeach module hypersonic inlet and the variation of angleof attacksideslip angle all lead to the nonuniform of the

flowfield at the entrance of isolators on the other hand thecombustion oscillation or deflagration all result in that thepressure at the exit of isolators shows uneven In contrast witha single-module engine the factors discussed above increasethe matching difficulty between the inlet and combustorcharacteristics for multiple-modules scramjet engines Theemphasis of this paper is to investigate the unstart couplingmechanism of multiple-modules hypersonic inlet due to thebackpressure of a single-module hypersonic inlet especiallyon how to interact with eachmodule by themassflow spillage

31 Unstarted Flowfield Structure Caused by Module II Throt-tling Firstly the unstarted flowfield structure caused bymodule II throttling was investigated Because the contour ofcross section 1198851 is the same as that of cross section 1198853 onlyone of them is presented Mach number contours of crosssection 1198851 and 1198852 in a buzz cycle are shown in Figure 4

As can be seen from the figure of 119905 = 0ms in Figure 4inlet is started though a small separated bubble is formed inentranceThe separated bubble is termed as ldquoinitial separatedbubblerdquo in order to facilitate the description below Theflowfield structure of the multiple-modules hypersonic inletgoes through four stages as follows

Stage I MassFilling Up (0sim05ms) A high pressure region isformed at the exit of module II due to throttling To matchwith the high backpressure a shock train in the isolator isformed Then the augment of the backpressure leads to thatthe shock train moves upstream At about 05ms the shocktrain leading edge is pushed to the inlet throat The coreflow which contains shock train moves downstream whileboundary layers shift upstream The flowfiled structures ofmodule I and module III however are distinct with that ofmodule II And no high backpressure no shock train and no

6 The Scientific World Journal

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 6 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

reversed flow are formed since there is no throttling at theirexits

Stage II Shock System Disgorging (05sim20ms) In module IIthe shock train is expelled from isolator when backpressureincreases to some extents leading to that the external shocksystemmoves upstream and the capturedmassflow descendsThe gradual increase of adverse pressure gradient results inthat the reversed flow occupies more and more part of theinternal flowfield until all flow is reversed and the velocityof reversed flow also increases gradually In addition theentrance part of inlet acts as a diverging duct for the reversedflow and thus the velocity of the reversed flow increasesfurther However no reversed flow emerges in the isolatorof module I and module III while the flow velocity reducesfrom supersonic to subsonic only a part of airflow enters theisolator due the spillage It is worth to note that module Iand module III are both unstarted and their external shocksystems are the same with that of module II though theirinternal flowfield structures are distinct

Stage III Shock System Swallowing (20sim40ms) Most ofairflow spills at stage II Then due to the imbalance betweenless captured mass flow and nearly unchanged dischargedmass flow a pressure trough is formed in the exit andpropagates upstream leading to that the shock systemmovesdownstream At this stage the reversed flow in the isolatorof module II occupies less gradually However there is nochange of flow direction in the isolator of module I andmodule III meanwhile flow velocity increases from subsonicto supersonic Although their internal flowfield structures are

distinct their external shock systems are the same and movedownstream together

Stage IV Duct Pressure Recovering (40sim45ms) The shocksystems reestablish but the pressure of duct is still lower thanthat at 119905 = 0ms With the captured airflow increasing thepressure ascends gradually At about 119905 = 45ms there isa local separated region at the exit of the isolator whichindicates that the pressure recovers that at 119905 = 0msThen thenext buzz cycle begins

According to the analysis of the four stages the unstartmechanism can be discussed simply The occurrence ofunstart is caused by the mass flow rate imbalance betweeninlet entrance and isolator exit The freestream conditionsand the conditions of isolator exit are fixed The flowfieldhowever oscillates all the time In buzz process the spillagechanges and plays an important role Thus the spillage is themajor disturbance source for hypersonic inlets which is alsoproposed by Tan et al [13] based on experimental results

The histories of mass-captured coefficient and staticpressure at the exit of isolator are given in Figure 5 As canbe seen from Figure 5 the buzz characteristic of module Iis the same with that of module III The dominant buzzfrequencies of three modules are 2213Hz indicating thattheir unstarted processes are synchronous The pressureamplitude of module II is higher than that of module I ormodule III and the mass flow rate amplitude of moduleII is lower since the throttling restricts it Thus unstartphenomenon of module II is much stronger

To understand the couple mechanism of unstarted flowfor the multiple-modules hypersonic inlet the flowfield

The Scientific World Journal 7

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

00 ms

(c)

05 ms

02 03 04 05 06

01

(d)

05 ms

02 03 04 05 06

01

(e)

02 03 04 05 06

01

05 ms

(f)

20 ms

02 03 04 05 06

01

(g)

20 ms

02 03 04 05 06

01

(h)

02 03 04 05 06

01

20 ms

(i)

40 ms

00 ms02 03 04 05 06

01

(j)

40 ms

00 ms02 03 04 05 06

01

(k)

02 03 04 05 06

01

40 ms

(l)

45 ms

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

01

(m)

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

0145 ms

(n)

02 03 04 05 06

05 10Mach number20 3015 25 35 4540

01

45 ms

(o)

Figure 7 Mach contours mixing with cross section 1198851 1198852 and 1198853 in a buzz cycle

structure of separated bubble in a buzz cycle was analyzedThe pressure contours with streamlines of cross section Y ina buzz cycle are shown in Figure 6

It can be noted that reversed streamlines emerge inentrance of all modules as shown in Figure 6(a)The reversedstreamlines are located in the initial separated bubble whichhave no influence on analysis of coupling mechanism sincethere is no transverse flow among modules In cross sectionY the intersection line of streamlines where airflow spillsbetween freestream and reversed flow is termed as spilledline in this paper Since reversed flow emerges in module IItwo weak vortexes are formed becoming stronger graduallywith an increase of reversed flow velocity as shown inFigures 6(b) and 6(c)When the reversed flow velocity is highenough spilled line is pushed upstream further and extendsto both sides leading to that the two side vortexes are in

the downstream of spilled line as shown in Figure 6(d) It isworth to note that a small part flow of vortexes enters sidemodules The increase of reversed flow velocity and moreairflow of side vortexes entering the side modules due to theupstreammovement of external shock system encourage twovortexes to expand further The middle part of spilled line ispushed upstreamwhile two-sides part is pushed downstreamwhich leads an arc spilled line to be formed as shownin Figure 6(e) Then external shock system starts movingdownstream The occupation proportion of the reversedflow decreases gradually and the reversed flow disappearseventuallyThe endpart of vortexes enters allmodules and thespilled line is dragged downstream as shown in Figure 6(f)When capturedmass flow increases to some extents the initialseparated bubble recovers gradually Thus the reversed flowof initial separated bubble emerges again and its velocity is

8 The Scientific World Journal

0 2 4 6 8 10 12 140

02

04

06

08

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

Module IModule IIModule III

(a) Mass-captured coefficient

0

05

1

15

2

0 2 4 6 8 10 12 14Time (ms)

Module IModule IIModule III

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 8 The histories of mass-captured coefficient and static pressure at the exit of isolator

higher than that of initial state This reversed flow generatestwo-side weak vortexes With the shock system movingdownstream further external shock system is reestablishedand the disturbance of initial separated bubble becomesweaker Thus the two side vortexes is smaller and smalleruntil disappear as shown in Figures 6(g) and 6(h) The initialseparated bubbles in three modules recover entirely at about45ms as shown in Figure 6(i) At this time transverse flowdisappears which indicates that there is no effect among threemodules

32 Unstarted Flowfield Structure Caused by Module IIIThrottling Next the unstarted flowfield structure caused bymodule III throttling was analyzed Figure 7 presents Machnumber contours of cross section 1198851 1198852 and 1198853 in a buzzcycle It is easy to find that unstarted process includes thesame four stages massfilling up (0sim05ms) shock systemdisgorging (05sim20ms) shock system swallowing (20sim40ms) and duct pressure recovering (40sim45ms)

Similarly the internal flowfield structures among differ-ent modules are distinct There is shock train formation andreversed flow appearance in the isolator of module III whilethese phenomena do not occur in module I and moduleII Their external shock systems are identical and are notdisturbed by internal flowfield

To understand the buzz differences among three mod-ules further the histories of mass-captured coefficient andstatic pressure at the exit are plotted in Figure 8 It iseasy to draw a conclusion that buzz processes of threemodules are synchronous and the dominant frequency is2289Hz while unstart phenomenon of module III is muchstronger

To understand how the unstarted flow of module IIIresults in unstart occurrences in module I and module II the

pressure contours mixing with streamlines of cross section 119884are analyzed and are presented in Figure 9

Similarly three modules do not affect each other sincethere is no transverse flow among modules at the beginningas shown in Figure 9(a) When the shock train arrives at thethroat upstream reversed flow emerges inmodule III leadingto that only one weak vortex is formed by the interactionbetween reversed flow and freestream With the externalshock system moving upstream the augment of adversepressure gradient caused by increasing spillage accelerates thereversed flowThus the vortex becomes bigger and the spilledline is pushed upstream as shown in Figures 9(b) and 9(c)When the vortex expands to some extent freestream ischocked which leads to that a new vortex located upstreamofspilled line is formedHereafter the adverse pressure gradientincreases slowly since duct pressure is low resulting in thatthe velocity of reversed flow increases slowly and more andmore airflow enters module I and module II In additionfreestream is accelerated in the aerodynamics throat which isformed between the two vortexes Thus the upstream vortexexpands with the external shock system moving upstreamfurther while the downstream vortex shrinks as shown inFigures 9(d) and 9(e) Then external shock system startsmoving downstream due to the formation of pressure troughin module III The velocity of reversed flow descends withexternal shock system moving downstream leading to thatthe downstream vortex shrinks gradually and disappearseventually as shown in Figure 9(f) At the same time thechocking effect also decreases gradually due to the shrink-age and the eventual disappearance of downstream vortexleading the upstream vortex to shrink and vanish Then anew and weak vortex is formed by the interaction betweenreversed flow and freestream as shown in Figure 9(g)The initial separated bubble recovers and reversed flowin the isolator of module III disappears gradually with

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

6 The Scientific World Journal

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 6 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

reversed flow are formed since there is no throttling at theirexits

Stage II Shock System Disgorging (05sim20ms) In module IIthe shock train is expelled from isolator when backpressureincreases to some extents leading to that the external shocksystemmoves upstream and the capturedmassflow descendsThe gradual increase of adverse pressure gradient results inthat the reversed flow occupies more and more part of theinternal flowfield until all flow is reversed and the velocityof reversed flow also increases gradually In addition theentrance part of inlet acts as a diverging duct for the reversedflow and thus the velocity of the reversed flow increasesfurther However no reversed flow emerges in the isolatorof module I and module III while the flow velocity reducesfrom supersonic to subsonic only a part of airflow enters theisolator due the spillage It is worth to note that module Iand module III are both unstarted and their external shocksystems are the same with that of module II though theirinternal flowfield structures are distinct

Stage III Shock System Swallowing (20sim40ms) Most ofairflow spills at stage II Then due to the imbalance betweenless captured mass flow and nearly unchanged dischargedmass flow a pressure trough is formed in the exit andpropagates upstream leading to that the shock systemmovesdownstream At this stage the reversed flow in the isolatorof module II occupies less gradually However there is nochange of flow direction in the isolator of module I andmodule III meanwhile flow velocity increases from subsonicto supersonic Although their internal flowfield structures are

distinct their external shock systems are the same and movedownstream together

Stage IV Duct Pressure Recovering (40sim45ms) The shocksystems reestablish but the pressure of duct is still lower thanthat at 119905 = 0ms With the captured airflow increasing thepressure ascends gradually At about 119905 = 45ms there isa local separated region at the exit of the isolator whichindicates that the pressure recovers that at 119905 = 0msThen thenext buzz cycle begins

According to the analysis of the four stages the unstartmechanism can be discussed simply The occurrence ofunstart is caused by the mass flow rate imbalance betweeninlet entrance and isolator exit The freestream conditionsand the conditions of isolator exit are fixed The flowfieldhowever oscillates all the time In buzz process the spillagechanges and plays an important role Thus the spillage is themajor disturbance source for hypersonic inlets which is alsoproposed by Tan et al [13] based on experimental results

The histories of mass-captured coefficient and staticpressure at the exit of isolator are given in Figure 5 As canbe seen from Figure 5 the buzz characteristic of module Iis the same with that of module III The dominant buzzfrequencies of three modules are 2213Hz indicating thattheir unstarted processes are synchronous The pressureamplitude of module II is higher than that of module I ormodule III and the mass flow rate amplitude of moduleII is lower since the throttling restricts it Thus unstartphenomenon of module II is much stronger

To understand the couple mechanism of unstarted flowfor the multiple-modules hypersonic inlet the flowfield

The Scientific World Journal 7

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

00 ms

(c)

05 ms

02 03 04 05 06

01

(d)

05 ms

02 03 04 05 06

01

(e)

02 03 04 05 06

01

05 ms

(f)

20 ms

02 03 04 05 06

01

(g)

20 ms

02 03 04 05 06

01

(h)

02 03 04 05 06

01

20 ms

(i)

40 ms

00 ms02 03 04 05 06

01

(j)

40 ms

00 ms02 03 04 05 06

01

(k)

02 03 04 05 06

01

40 ms

(l)

45 ms

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

01

(m)

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

0145 ms

(n)

02 03 04 05 06

05 10Mach number20 3015 25 35 4540

01

45 ms

(o)

Figure 7 Mach contours mixing with cross section 1198851 1198852 and 1198853 in a buzz cycle

structure of separated bubble in a buzz cycle was analyzedThe pressure contours with streamlines of cross section Y ina buzz cycle are shown in Figure 6

It can be noted that reversed streamlines emerge inentrance of all modules as shown in Figure 6(a)The reversedstreamlines are located in the initial separated bubble whichhave no influence on analysis of coupling mechanism sincethere is no transverse flow among modules In cross sectionY the intersection line of streamlines where airflow spillsbetween freestream and reversed flow is termed as spilledline in this paper Since reversed flow emerges in module IItwo weak vortexes are formed becoming stronger graduallywith an increase of reversed flow velocity as shown inFigures 6(b) and 6(c)When the reversed flow velocity is highenough spilled line is pushed upstream further and extendsto both sides leading to that the two side vortexes are in

the downstream of spilled line as shown in Figure 6(d) It isworth to note that a small part flow of vortexes enters sidemodules The increase of reversed flow velocity and moreairflow of side vortexes entering the side modules due to theupstreammovement of external shock system encourage twovortexes to expand further The middle part of spilled line ispushed upstreamwhile two-sides part is pushed downstreamwhich leads an arc spilled line to be formed as shownin Figure 6(e) Then external shock system starts movingdownstream The occupation proportion of the reversedflow decreases gradually and the reversed flow disappearseventuallyThe endpart of vortexes enters allmodules and thespilled line is dragged downstream as shown in Figure 6(f)When capturedmass flow increases to some extents the initialseparated bubble recovers gradually Thus the reversed flowof initial separated bubble emerges again and its velocity is

8 The Scientific World Journal

0 2 4 6 8 10 12 140

02

04

06

08

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

Module IModule IIModule III

(a) Mass-captured coefficient

0

05

1

15

2

0 2 4 6 8 10 12 14Time (ms)

Module IModule IIModule III

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 8 The histories of mass-captured coefficient and static pressure at the exit of isolator

higher than that of initial state This reversed flow generatestwo-side weak vortexes With the shock system movingdownstream further external shock system is reestablishedand the disturbance of initial separated bubble becomesweaker Thus the two side vortexes is smaller and smalleruntil disappear as shown in Figures 6(g) and 6(h) The initialseparated bubbles in three modules recover entirely at about45ms as shown in Figure 6(i) At this time transverse flowdisappears which indicates that there is no effect among threemodules

32 Unstarted Flowfield Structure Caused by Module IIIThrottling Next the unstarted flowfield structure caused bymodule III throttling was analyzed Figure 7 presents Machnumber contours of cross section 1198851 1198852 and 1198853 in a buzzcycle It is easy to find that unstarted process includes thesame four stages massfilling up (0sim05ms) shock systemdisgorging (05sim20ms) shock system swallowing (20sim40ms) and duct pressure recovering (40sim45ms)

Similarly the internal flowfield structures among differ-ent modules are distinct There is shock train formation andreversed flow appearance in the isolator of module III whilethese phenomena do not occur in module I and moduleII Their external shock systems are identical and are notdisturbed by internal flowfield

To understand the buzz differences among three mod-ules further the histories of mass-captured coefficient andstatic pressure at the exit are plotted in Figure 8 It iseasy to draw a conclusion that buzz processes of threemodules are synchronous and the dominant frequency is2289Hz while unstart phenomenon of module III is muchstronger

To understand how the unstarted flow of module IIIresults in unstart occurrences in module I and module II the

pressure contours mixing with streamlines of cross section 119884are analyzed and are presented in Figure 9

Similarly three modules do not affect each other sincethere is no transverse flow among modules at the beginningas shown in Figure 9(a) When the shock train arrives at thethroat upstream reversed flow emerges inmodule III leadingto that only one weak vortex is formed by the interactionbetween reversed flow and freestream With the externalshock system moving upstream the augment of adversepressure gradient caused by increasing spillage accelerates thereversed flowThus the vortex becomes bigger and the spilledline is pushed upstream as shown in Figures 9(b) and 9(c)When the vortex expands to some extent freestream ischocked which leads to that a new vortex located upstreamofspilled line is formedHereafter the adverse pressure gradientincreases slowly since duct pressure is low resulting in thatthe velocity of reversed flow increases slowly and more andmore airflow enters module I and module II In additionfreestream is accelerated in the aerodynamics throat which isformed between the two vortexes Thus the upstream vortexexpands with the external shock system moving upstreamfurther while the downstream vortex shrinks as shown inFigures 9(d) and 9(e) Then external shock system startsmoving downstream due to the formation of pressure troughin module III The velocity of reversed flow descends withexternal shock system moving downstream leading to thatthe downstream vortex shrinks gradually and disappearseventually as shown in Figure 9(f) At the same time thechocking effect also decreases gradually due to the shrink-age and the eventual disappearance of downstream vortexleading the upstream vortex to shrink and vanish Then anew and weak vortex is formed by the interaction betweenreversed flow and freestream as shown in Figure 9(g)The initial separated bubble recovers and reversed flowin the isolator of module III disappears gradually with

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

The Scientific World Journal 7

01

02 03 04 05 06

00 ms

(a)

01

02 03 04 05 06

00 ms

(b)

01

02 03 04 05 06

00 ms

(c)

05 ms

02 03 04 05 06

01

(d)

05 ms

02 03 04 05 06

01

(e)

02 03 04 05 06

01

05 ms

(f)

20 ms

02 03 04 05 06

01

(g)

20 ms

02 03 04 05 06

01

(h)

02 03 04 05 06

01

20 ms

(i)

40 ms

00 ms02 03 04 05 06

01

(j)

40 ms

00 ms02 03 04 05 06

01

(k)

02 03 04 05 06

01

40 ms

(l)

45 ms

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

01

(m)

02 03 04 05 06

05 10Mach number

20 3015 25 35 4540

0145 ms

(n)

02 03 04 05 06

05 10Mach number20 3015 25 35 4540

01

45 ms

(o)

Figure 7 Mach contours mixing with cross section 1198851 1198852 and 1198853 in a buzz cycle

structure of separated bubble in a buzz cycle was analyzedThe pressure contours with streamlines of cross section Y ina buzz cycle are shown in Figure 6

It can be noted that reversed streamlines emerge inentrance of all modules as shown in Figure 6(a)The reversedstreamlines are located in the initial separated bubble whichhave no influence on analysis of coupling mechanism sincethere is no transverse flow among modules In cross sectionY the intersection line of streamlines where airflow spillsbetween freestream and reversed flow is termed as spilledline in this paper Since reversed flow emerges in module IItwo weak vortexes are formed becoming stronger graduallywith an increase of reversed flow velocity as shown inFigures 6(b) and 6(c)When the reversed flow velocity is highenough spilled line is pushed upstream further and extendsto both sides leading to that the two side vortexes are in

the downstream of spilled line as shown in Figure 6(d) It isworth to note that a small part flow of vortexes enters sidemodules The increase of reversed flow velocity and moreairflow of side vortexes entering the side modules due to theupstreammovement of external shock system encourage twovortexes to expand further The middle part of spilled line ispushed upstreamwhile two-sides part is pushed downstreamwhich leads an arc spilled line to be formed as shownin Figure 6(e) Then external shock system starts movingdownstream The occupation proportion of the reversedflow decreases gradually and the reversed flow disappearseventuallyThe endpart of vortexes enters allmodules and thespilled line is dragged downstream as shown in Figure 6(f)When capturedmass flow increases to some extents the initialseparated bubble recovers gradually Thus the reversed flowof initial separated bubble emerges again and its velocity is

8 The Scientific World Journal

0 2 4 6 8 10 12 140

02

04

06

08

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

Module IModule IIModule III

(a) Mass-captured coefficient

0

05

1

15

2

0 2 4 6 8 10 12 14Time (ms)

Module IModule IIModule III

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 8 The histories of mass-captured coefficient and static pressure at the exit of isolator

higher than that of initial state This reversed flow generatestwo-side weak vortexes With the shock system movingdownstream further external shock system is reestablishedand the disturbance of initial separated bubble becomesweaker Thus the two side vortexes is smaller and smalleruntil disappear as shown in Figures 6(g) and 6(h) The initialseparated bubbles in three modules recover entirely at about45ms as shown in Figure 6(i) At this time transverse flowdisappears which indicates that there is no effect among threemodules

32 Unstarted Flowfield Structure Caused by Module IIIThrottling Next the unstarted flowfield structure caused bymodule III throttling was analyzed Figure 7 presents Machnumber contours of cross section 1198851 1198852 and 1198853 in a buzzcycle It is easy to find that unstarted process includes thesame four stages massfilling up (0sim05ms) shock systemdisgorging (05sim20ms) shock system swallowing (20sim40ms) and duct pressure recovering (40sim45ms)

Similarly the internal flowfield structures among differ-ent modules are distinct There is shock train formation andreversed flow appearance in the isolator of module III whilethese phenomena do not occur in module I and moduleII Their external shock systems are identical and are notdisturbed by internal flowfield

To understand the buzz differences among three mod-ules further the histories of mass-captured coefficient andstatic pressure at the exit are plotted in Figure 8 It iseasy to draw a conclusion that buzz processes of threemodules are synchronous and the dominant frequency is2289Hz while unstart phenomenon of module III is muchstronger

To understand how the unstarted flow of module IIIresults in unstart occurrences in module I and module II the

pressure contours mixing with streamlines of cross section 119884are analyzed and are presented in Figure 9

Similarly three modules do not affect each other sincethere is no transverse flow among modules at the beginningas shown in Figure 9(a) When the shock train arrives at thethroat upstream reversed flow emerges inmodule III leadingto that only one weak vortex is formed by the interactionbetween reversed flow and freestream With the externalshock system moving upstream the augment of adversepressure gradient caused by increasing spillage accelerates thereversed flowThus the vortex becomes bigger and the spilledline is pushed upstream as shown in Figures 9(b) and 9(c)When the vortex expands to some extent freestream ischocked which leads to that a new vortex located upstreamofspilled line is formedHereafter the adverse pressure gradientincreases slowly since duct pressure is low resulting in thatthe velocity of reversed flow increases slowly and more andmore airflow enters module I and module II In additionfreestream is accelerated in the aerodynamics throat which isformed between the two vortexes Thus the upstream vortexexpands with the external shock system moving upstreamfurther while the downstream vortex shrinks as shown inFigures 9(d) and 9(e) Then external shock system startsmoving downstream due to the formation of pressure troughin module III The velocity of reversed flow descends withexternal shock system moving downstream leading to thatthe downstream vortex shrinks gradually and disappearseventually as shown in Figure 9(f) At the same time thechocking effect also decreases gradually due to the shrink-age and the eventual disappearance of downstream vortexleading the upstream vortex to shrink and vanish Then anew and weak vortex is formed by the interaction betweenreversed flow and freestream as shown in Figure 9(g)The initial separated bubble recovers and reversed flowin the isolator of module III disappears gradually with

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 The Scientific World Journal

0 2 4 6 8 10 12 140

02

04

06

08

Time (ms)

Mas

s-ca

ptur

ed co

effici

ent

Module IModule IIModule III

(a) Mass-captured coefficient

0

05

1

15

2

0 2 4 6 8 10 12 14Time (ms)

Module IModule IIModule III

Stat

ic p

ress

ure (

105Pa

)(b) Static pressure

Figure 8 The histories of mass-captured coefficient and static pressure at the exit of isolator

higher than that of initial state This reversed flow generatestwo-side weak vortexes With the shock system movingdownstream further external shock system is reestablishedand the disturbance of initial separated bubble becomesweaker Thus the two side vortexes is smaller and smalleruntil disappear as shown in Figures 6(g) and 6(h) The initialseparated bubbles in three modules recover entirely at about45ms as shown in Figure 6(i) At this time transverse flowdisappears which indicates that there is no effect among threemodules

32 Unstarted Flowfield Structure Caused by Module IIIThrottling Next the unstarted flowfield structure caused bymodule III throttling was analyzed Figure 7 presents Machnumber contours of cross section 1198851 1198852 and 1198853 in a buzzcycle It is easy to find that unstarted process includes thesame four stages massfilling up (0sim05ms) shock systemdisgorging (05sim20ms) shock system swallowing (20sim40ms) and duct pressure recovering (40sim45ms)

Similarly the internal flowfield structures among differ-ent modules are distinct There is shock train formation andreversed flow appearance in the isolator of module III whilethese phenomena do not occur in module I and moduleII Their external shock systems are identical and are notdisturbed by internal flowfield

To understand the buzz differences among three mod-ules further the histories of mass-captured coefficient andstatic pressure at the exit are plotted in Figure 8 It iseasy to draw a conclusion that buzz processes of threemodules are synchronous and the dominant frequency is2289Hz while unstart phenomenon of module III is muchstronger

To understand how the unstarted flow of module IIIresults in unstart occurrences in module I and module II the

pressure contours mixing with streamlines of cross section 119884are analyzed and are presented in Figure 9

Similarly three modules do not affect each other sincethere is no transverse flow among modules at the beginningas shown in Figure 9(a) When the shock train arrives at thethroat upstream reversed flow emerges inmodule III leadingto that only one weak vortex is formed by the interactionbetween reversed flow and freestream With the externalshock system moving upstream the augment of adversepressure gradient caused by increasing spillage accelerates thereversed flowThus the vortex becomes bigger and the spilledline is pushed upstream as shown in Figures 9(b) and 9(c)When the vortex expands to some extent freestream ischocked which leads to that a new vortex located upstreamofspilled line is formedHereafter the adverse pressure gradientincreases slowly since duct pressure is low resulting in thatthe velocity of reversed flow increases slowly and more andmore airflow enters module I and module II In additionfreestream is accelerated in the aerodynamics throat which isformed between the two vortexes Thus the upstream vortexexpands with the external shock system moving upstreamfurther while the downstream vortex shrinks as shown inFigures 9(d) and 9(e) Then external shock system startsmoving downstream due to the formation of pressure troughin module III The velocity of reversed flow descends withexternal shock system moving downstream leading to thatthe downstream vortex shrinks gradually and disappearseventually as shown in Figure 9(f) At the same time thechocking effect also decreases gradually due to the shrink-age and the eventual disappearance of downstream vortexleading the upstream vortex to shrink and vanish Then anew and weak vortex is formed by the interaction betweenreversed flow and freestream as shown in Figure 9(g)The initial separated bubble recovers and reversed flowin the isolator of module III disappears gradually with

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

The Scientific World Journal 9

002

0

03 035 04

(a)

002

0

03 035 04

(b)

002

0

03 035 04

(c)

002

0

03 035 04

(d)

002

0

03 035 04

(e)

002

0

03 035 04

(f)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(g)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(h)

002

0

03 035 04

2000 6000 10000Pressure

14000 18000

(i)

Figure 9 Static pressure contours mixing with streamlines of cross section 119884 in a buzz cycle

the external shock system moving downstream further Thusthe transverse flow among three modules is weaker andweaker and the initial separated bubble recovers entirely atabout 45ms as shown in Figure 9(i) At this time transverseflow disappears which indicates that there is no interactionamong three modules

As discussed above the unstarted coupling mechanismamong three uniform although a module is chocked Henceit has little contribution on the formation of transversevortexes and it indicates and verifies that the external shocksystem is identical at the same time The reversed flowin isolator however dominates the formation expansionshrinkage and disappearance of the vortexes Thus it isthe major factor of unstart coupling of multiple-moduleshypersonic inlet

4 Conclusion

The combination of multiplemodules in parallel manner isan important way to achieve the much higher thrust ofscramjet engine and the unstart coupling mechanism andcharacteristic among multiple modules hypersonic inlet is animportant issue The unstarted flowfield and coupling char-acteristic of three-module hypersonic inlet caused by centermodule II and side module III were conducted respectivelyThe results show that the other two modules hypersonic inletare forced into unstarted flow when unstarted phenomenonappears on a single-module hypersonic inlet due to highbackpressure Vortexes act as a bond among three modulesin the whole unstarted process The transverse pressuredistribution on the cross section 119884 caused by throttling

is almost uniform and hence it has little contribution onthe formation of transverse vortexes and it indicates andverifies that the external shock system is identical How-ever the reversed flow in isolator dominates the formationexpansion shrinkage and disappearance of the vortexes andthus it is the major factor of unstart coupling of multiplemodules hypersonic inlet The coupling effect among mul-tiple modules makes hypersonic inlet be easier to result inunstart

Acknowledgment

This work was supported by The National Natural ScienceFoundation of china (no 11372092 and no 51121004)

References

[1] C R McClinton J L Hunt and R H Ricketts ldquoAirbreath-ing hypersonic technology vision vehicles and developmentdreamsrdquo AIAA Paper 1999-4978 1999

[2] R T Voland AHAuslenderMK Smart A S Roudakov V LSemenov and V Kopchenov ldquoCIAMNASAMach 65 scramjetf light and ground testrdquo AIAA Paper 1999-4848 1999

[3] S H Walker F Rodgers and A Paull ldquoHyCAUSE flight testprogramrdquo AIAA Paper 2008-2580 2008

[4] R Mutzman and S Murphy ldquoX-51 development a chief engi-neerrsquos perspectiverdquo in Proceedings of the 17th AIAA InternationalSpace Planes and Hypersonic Systems and Technologies Confer-ence April 2011

[5] D Yu J Chang W Bao and Z Xie ldquoOptimal classification cri-terions of hypersonic inlet startunstartrdquo Journal of Propulsionand Power vol 23 no 2 pp 310ndash316 2007

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

10 The Scientific World Journal

[6] J Chang D Yu W Bao and Y Fan ldquoOperation pattern classi-fication of hypersonic inletsrdquoActa Astronautica vol 65 no 3-4pp 457ndash466 2009

[7] J Chang D Yu W Bao Z Xie and Y Fan ldquoA CFD assessmentof classifications for hypersonic inlet startunstart phenomenardquoAeronautical Journal vol 113 no 1142 pp 263ndash271 2009

[8] J Chang D Yu W Bao Y Fan and Y Shen ldquoEffects ofboundary-layers bleeding on unstartrestart characteristics ofhypersonic inletsrdquo Aeronautical Journal vol 113 no 1143 pp319ndash327 2009

[9] D M Van Wie and F T Kwok ldquoStarting characteristics ofsupersonic inletsrdquo AIAA Paper 1996-2914 1996

[10] J L Wagner K B Yuceil A Valdivia N T Clemens and D SDolling ldquoExperimental investigation of unstart in an inletisolator model in mach 5 flowrdquo AIAA Journal vol 47 no 6 pp1528ndash1542 2009

[11] T Shimura TMitani N Sakuranaka andM Izumikawa ldquoLoadoscillations caused by unstart of hypersonic wind tunnels andenginesrdquo Journal of Propulsion and Power vol 14 no 3 pp 348ndash353 1998

[12] S Trapier S Deck P Duveau and P Sagaut ldquoTime-frequencyanalysis and detection of supersonic inlet buzzrdquo AIAA Journalvol 45 no 9 pp 2273ndash2284 2007

[13] H-J Tan S Sun andZ-L Yin ldquoOscillatory flows of rectangularhypersonic inlet unstart caused by downstream mass-flowchokingrdquo Journal of Propulsion and Power vol 25 no 1 pp 138ndash147 2009

[14] B T Campbell A Siebenhaar and T Nguyen ldquoStrutjet engineperformancerdquo Journal of Propulsion and Power vol 17 no 6 pp1227ndash1232 2001

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of