a combustor-representative swirl simulator for a transonic turbine research facility

A combustor-representative swirl simulatorfor a transonic turbine research facilityI Qureshi* and T Povey

Department of Engineering Science, University of Oxford, Oxford, UK

The manuscript was received on 30 July 2010 and was accepted after revision for publication on 27 January 2011.

DOI: 10.1177/0954410011400817

Abstract: Tighter aircraft emissions regulations have let to considerable improvement in gasturbine combustion in the past few decades. Modern combustors employ aggressive swirlers toincrease mixing and to improve flame stability during the combustion process. The flow at com-bustor exit can therefore have high residual swirl. The impact of this swirl on the aerodynamicand heat transfer characteristics of the HP turbine stage has not yet received much attention.

In order to investigate the effects of swirl on the HP turbine stage, an inlet swirl simulator hasbeen designed and commissioned in an engine scale, short duration, rotating transonic turbinefacility. The test facility simulates engine representative Mach number, Reynolds number, non-dimensional speed and gas-to-wall temperature ratio at the turbine inlet. The target swirl profileat turbine stage inlet was based upon extreme exit swirl conditions for a modern low-NOx com-bustor with peak yaw and pitch angles over �40�. A number of candidate swirler designs wereconsidered during a pilot study that was conducted in a subsonic wind tunnel to achieve suitableswirler design. The swirl simulator was developed based upon the pilot study results, whichachieved a good match to the target profile after commissioning in the facility. This articlemainly deals with the design and development of the swirl generator. It presents the experimentaland computational results of the pilot study, followed by the description of the installation andcommissioning of the swirl simulator on the test facility. Novel instrumentation was required tosurvey the swirl profile, which is also described. A comparison of the measured and computa-tional aerodynamic results with and without swirl, at 10 per cent and 90 per cent span of HPnozzle guide vane is also presented. The comparison highlights significant impact of swirl on thevane incidence angle, and therefore a considerable affect on the loading distribution of the vane.

Keywords: transonic turbine, gas turbine, combustor swirl, HP turbine

1 INTRODUCTION

Swirling flows are now commonly used to stabilize

the combustion process in modern gas turbine

engines. Swirling flow gives rise to radial and axial

static pressure gradients within the combustion

chamber. In the case of strong swirl, the adverse

axial pressure gradient can be sufficiently large to

cause reverse flow along the direction of the turbine

axis, giving rise to a central recirculation zone [1]. The

recirculation zone plays an important role in flame

stabilization process by providing a hot, low velocity

region of combustion products [2].

Numerous experimental studies have been

reported which investigate the effects of swirl on

combustion and emission characteristics, e.g. refer-

ences [3–5]. Numerical investigations have also been

reported regarding the flow dynamics in swirl-stabi-

lized combustors, e.g. references [6–8]. There is very

little published literature that focuses on the effects of

*Corresponding author: Department of Engineering Science,

University of Oxford, Parks Road, Oxford, OX1 3PJ, UK.

email: [email protected]

1

Proc. IMechE Vol. 000 Part G: J. Aerospace Engineering

at University of Oxford on June 18, 2011pig.sagepub.comDownloaded from

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combustor swirl on the flow characteristics of the

high-pressure turbine.

Velocity measurements performed in gas turbine

combustors with high swirl at inlet confirm the per-

sistence of swirl at the combustion chamber exit

plane [9, 10]. This highlights the need to explore the

effects of swirl on the downstream turbine. A com-

bustion chamber model with swirling flows has been

recently developed by Wurm et al. [11] in order to

study the effect of swirl on combustor cooling

schemes. Also, a combustor simulator model has

been used to study the flow and thermal field gener-

ated at combustor exit and/or its effects on the

turbine [12–15], however, the focus of these studies

had been the effects of the combustor dilution jets

and turbulence; the upstream swirlers were not sim-

ulated. Van Fossen and Bunker [16] investigated

the level of stagnation region heat transfer augmen-

tation due to turbulence from a can-type combustor

incorporating fuel/air swirlers. Heat transfer rate

augmentation of 77 per cent compared to that pre-

dicted computationally in the laminar situation was

observed. The numerical study performed by Shih

[17] highlights the effect of inlet swirl on the aerody-

namic and heat transfer characteristics of turbine

nozzle guide vane (NGV) and endwall.

The objective of this study was to design an engine-

representative swirl simulator and install it on the

Oxford Turbine Research Facility (OTRF), so as to

be able to carry out detailed experimental investiga-

tions of the high-pressure turbine stage with inlet

swirl. The design and commissioning of the inlet

swirl simulator is the subject of this article.

2 OXFORD TURBINE RESEARCH FACILITY

The OTRF is a short-duration wind tunnel capable of

testing an engine-scale high-pressure turbine stage

(MT1 turbine stage installed for current investiga-

tions) at non-dimensionally representative condi-

tions. M, Re, Tu, Tg /Tw, and N� ffiffiffiffi

Tp

are matched

to engine conditions. The main components of

the facility include: (1) the high-pressure reservoir;

(2) the pump-tube with a light-weight piston; (3) a

fast acting plug valve; (4) the turbine stage (working

section) and; (5) the turbobrake. These are indicated

in the schematic of the test facility shown in Fig. 1.

The operating principles of this type of facility are

described by Jones et al. [18].

Prior to an experimental run the plug valve is

closed, the working section and exhaust tank are

evacuated, and the turbine disk is accelerated to the

design speed using an air motor. Air from the high-

pressure reservoir is injected into the piston tube

behind the light piston. Under the action of the

injected gas, the piston is driven down the piston

tube compressing and heating the air in front of it.

The process is approximately isentropic. When the

desired working section pressure is achieved, the

fast-acting plug valve is opened and the test gas

(air) flows out of the piston tube into a large annular

flow-path, then through a contraction which forms

the inlet to the turbine stage. The test run ends

when the piston reaches the end of the piston tube.

Steady conditions are achieved for approximately

500 ms, during which the experimental data is

acquired. The torque developed in the turbine is

opposed by a turbobrake [19], which is on the same

shaft as the turbine and is driven by the turbine exit

flow. Thus, approximately constant speed is main-

tained during the 500 ms test period. The general

operating conditions for the OTRF are listed in

Table 1.

The OTRF has been used to test a number of HP

turbine stages, e.g. reference [20] and also 1.5 stage

configurations, e.g. reference [21]. This study was

part of the EU Turbine Aero-thermal External Flows

II (TATEF II) programme. The wider aim of this

research programme was to study the impact of com-

bustor representative flows on the aerodynamic per-

formance and heat transfer of HP turbine. Therefore,

as part of this study, the OTRF was also upgraded to

include a temperature distortion generator [22–25],

an efficiency measurement system [26, 27] along

with the development of the swirl generator.

Fig. 1 Schematic of OTRF

Table 1 Turbine stage operating conditions for OTRF

Parameter (unit)Nominalvalue

Allowable run-to-runvariations aroundnominal value (%)

P01 (bar) 4.6 �1T01 (K) 444 �2Tg/Tw 1.50 �2

M hub2 1.054 �1

Mcasing2 0.912 �1

! (r/min) 9500 �1p02rel (bar) 2.697 �1

2 I Qureshi and T Povey




This article considers the development and

commissioning of the swirl generator.

3 TARGET SWIRL PROFILE

The target swirl profile was based on extreme exit

swirl conditions for a modern low-NOx combustor.

Figure 2 represents the swirl vectors, over one swirler

pitch, for the target profile at the NGV inlet plane,

when viewed from upstream to downstream.

To aid in computational fluid dynamics (CFD)

comparison, and to allow repeatability assessment

around the annulus, an integer swirler to vane

count ratio of 1:2 was chosen (16 swirlers for 32

NGVs of MT1 turbine stage).

The target swirl angle distributions at 20 per cent

and 80 per cent radial span (from Fig. 2) are shown in

Fig. 3. The horizontal axis represents two NGV pitches

(equal to one swirler pitch). The peak swirl angles

(approximately �40�) were set as a minimum target

to achieve in the test facility.

4 PILOT STUDY FOR SWIRLER DESIGN

A pilot study was conducted to assess candidate swir-

ler designs. The pilot study was performed in a sub-

sonic wind tunnel at the University of Oxford. The

wind tunnel was designed with a two-dimensional

analogue of the inlet contraction of MT1 HP turbine

stage. The vanes were not modelled. A schematic of

the test section of the tunnel used for pilot study is

shown in Fig. 4. The width of the tunnel was equiva-

lent to six vane passages, or three swirler pitches. The

location of the swirl generators is indicated in Fig. 4.

Four-hole pressure probes were used to measure

the swirl profile at NGV inlet plane. A truncated pyr-

amid pressure probe design was used, with an exter-

nal diameter of 5 mm and the side faces inclined at

45� as shown in Fig. 5. The description of the use of a

four-hole pyramid probe can be found in references

[28] and [29]. The probe was calibrated using a

subsonic probe calibration facility at the University

of Oxford [30] in the pitch and yaw angle range of

�50� to þ50� with a 1� step.

The contours of port pressure measured at the four

holes of the probe (normalized by the dynamic head),

over the calibrated range of pitch and yaw angles, are

shown in Fig. 6. Dimensionless calibration coeffi-

cients defined using the conventional method are

restricted to relatively low flow angles due to the

singularity encountered when the denominator in

the expressions approaches zero [30]. The objective

was to simulate a swirl profile with high flow angles

Fig. 2 Target swirl profile vectors

Fig. 3 Target yaw angle distributions at 20% and 80%radial span

Fig. 4 Schematic of pilot study wind tunnel testsection

Fig. 5 Four-hole pyramid probe (front view)

A combustor-representative swirl simulator 3




(�40� and above). To avoid singularities in the cali-

bration coefficients the flow coefficients were defined

as given below.

Yaw coefficient: C� ¼ðpc � pd Þ

ðpa � pminÞ

Pitch coefficient: C� ¼pa �

12 ðpc þ pd Þ

ðpa � pminÞ

Total pressure coefficient: CT ¼ðp0 � paÞ

ðpa � pminÞ

Dynamic pressure coefficient: CD ¼

12 �u2

ðpa � pminÞ

Here pmin is the minimum pressure of the outer

holes (b, c, d) at a given pitch/yaw combination.

Over the pitch and yaw angle range of �50� to þ50�

the denominator does not pass through zero. The

computed pitch and yaw coefficient maps (as defined

above) are shown in Fig. 7, as a function of pitch and

yaw. It is clear from the figures that there is a clean

calibration over most of the range: the contours are

approximately perpendicular to each other and gra-

dients are within a limited range. The process error in

pitch and yaw angles under steady flow conditions,

estimated by the back-substitution of probe calibra-

tion data into the calibration maps, was found to be

within �0.5� over the range considered.

A number of swirler designs were investigated

during the pilot study. For each design, a row of

three swirlers was tested so that approximately peri-

odic boundary conditions were established for the

central swirler. The downstream flow was surveyed

at the axial location of the NGV inlet plane using an

automated two-axis traverse system.

The final prototype swirler design, capable of gen-

erating the target swirl profile, is shown in Fig. 8. The

design was composed of six flat-plate vanes, fitted

between a central hub and an outer casing, each

vane inclined at 40� to the axial direction. The swirlers

were located in circular holes within a blockage plate.

The pitch and yaw angle profiles measured in the

pilot study are presented in Figs 9 and 10, respec-

tively. The plots cover region equivalent to the central

two NGV pitches (central swirler pitch). The dots

represent the points where experimental data were

collected. The orientation used for the flow angles is

shown in Fig. 11. The regions nearest to the hub and

casing walls where the data could not be obtained has

been filled with the results at the nearest measured

locations in the area plots. Positive values of pitch

angle (between 0 and 1 in NGV pitch in Fig. 9) indicate

Fig. 6 Pressure maps measured at the holes a, b, c,and d over a range of pitch and yaw covering�50� to þ50�

Fig. 7 Yaw and pitch calibration coefficients

Fig. 8 Model of final swirler design





the flow turning upwards and negative values

(between 1 and 2 in NGV pitch in Fig. 9) indicate

the flow turning downwards. This corresponds to

clockwise swirl. Similarly, positive and negative yaw

between 0.5 and 1 span and 0 and 0.5 span, respec-

tively (in Fig. 10) corresponds to clockwise swirl.

Maximum pitch and yaw angles of approximately

�50� were measured.

The measured swirl vectors, based upon the sec-

ondary flow velocity components obtained using

the measured flow angles, are shown in Fig. 12. A

clean clockwise vortex is formed (viewed from

upstream towards downstream).

5 SWIRLER CFD ANALYSIS

The swirl generator was investigated computationally

to aid interpretation of the results from the pilot

study. The computational analysis was performed

using the commercial CFD code Fluent. The pre-pro-

cessor Gambit was used to model and mesh the

working section of the pilot study tunnel. The mod-

elled geometry included the working section, three

swirlers, and the tunnel inlet contraction. An unstruc-

tured mesh with approximately 1 million tetrahedral

elements was used. The computational grid is shown

in Fig. 13. The mesh density was enhanced in regions

around and downstream of the swirlers.

The analysis was carried out using k-epsilon turbu-

lence model in the Fluent solver and the option for

intense swirling flow was used. The results obtained

from the analysis are given below. Figure 14 shows

the CFD predicted secondary flow vectors at the loca-

tion of the NGV inlet plane. The predicted clockwise

vortex compares very well with the measured results

presented in Fig. 12.

Fig. 9 Measured pitch angle profile; pilot study

Fig. 10 Measured yaw angle profile; pilot study

Fig. 11 Orientation of yaw (�) and pitch (�) angles

Fig. 12 Secondary flow vectors profile; pilot study

Fig. 13 Computational mesh comprising tunnel work-ing section and swirlers





The predicted swirl (yaw) angle distribution at 20

and 80 per cent span is compared to the experimen-

tally measured profile (from the pilot study) and the

target profile in Fig. 15. There is good agreement in

the general form of the profiles, but CFD underpre-

dicts the peak yaw angle by approximately 10�, and

overpredicts the minimum yaw angle by approxi-

mately 10�. This suggests greater mixing in the CFD

than in the experiment, with a broadening of the

vortex core. This is also illustrated by comparison of

Figs 12 and 14.

6 INLET SWIRL GENERATOR

The inlet swirl generator for the OTRF was developed

as a high-working-pressure module which incorpo-

rated the final swirler geometry. The module was

designed to mount in the tunnel flow path upstream

of the OTRF inlet contraction. The swirlers were

machined and fabricated (tungsten inert gas (TIG)

welded) from steel sheet and rod. A single fabricated

swirler is shown in Fig. 16.

The hub and case pressure housing rings were

machined from aluminium alloy. The swirlers were

assembled with an interference fit into the annular

containing ring and were TIG welded to form a

single-swirl generator ring, rotatable with respect to

the annular containing ring, so that clocking of the

vortex core with respect to the NGV leading edge

was possible. The outer diameter of the module was

approximately 1 m.

7 COMMISSIONING OF THE INLET SWIRL

GENERATOR

The inlet swirl generation system was installed in the

OTRF as shown in Fig. 17. The figure shows the swirl

generator with the HP turbine section removed.

Two rakes of four-hole probes (one with 5 probe

heads and other with 4 probe heads) were manufac-

tured for swirl profile measurements in the OTRF.

The probes are shown in Fig. 18. The probes heads

(with integral stem) were manufactured using metal

laser sintering and were mounted to holders manu-

factured using stereo-lithography. The probe heads

were instrumented using pneumatic tubing. Using

Fig. 14 Secondary flow vectors profile; CFD

Fig. 15 Yaw angle distribution at 20% and 80% span:comparison of CFD predictions, pilot studymeasurements and the target profile

Fig. 16 A fabricated swirler

Fig. 17 Inlet swirl generation system installed in theOTRF with the turbine module removed





the two probes, 9 radial locations could be measured

at each circumferential position.

Measurements were conducted at 10 circumferen-

tial locations (90 measurement points) over 1 swirler

pitch (2 NGV pitches). The measurement plane was

0.7 axial chords upstream of the vane inlet plane. The

calibration maps for each of the 9 four-hole probe

heads were generated as described in section 4. It is

interesting to note that the effect of the unusual probe

geometry (probes with 4 and 5 heads) on the individ-

ual probe calibrations was minimal. The calibrations

of the 9 probe heads were very similar to each other

(in the correct angular reference frame).

The flow measurements conducted using the four-

hole probes used static pressure differences between

the holes of the probe. In the normal blow-down oper-

ating mode of OTRF, there are fluctuations in total

pressure of approximately �1 per cent of inlet total

pressure (4.6 bar). The fluctuations (approximately

�4.6 kPa) are caused by piston oscillations, and are

illustrated in Fig. 19. In this mode, the pressure oscil-

lations caused by piston oscillations are greater than

the steady state difference in pressure between holes

caused by flow incidence in the highly swirling flow: at

the measurement plane the Mach number is approx-

imately 0.1, corresponding to a dynamic head equal to

0.7 per cent of the inlet total pressure. Thus, small dif-

ferences in phase lag between individual holes on a

given probe gave rise to significant discrepancies

from the steady state measurement.

To reduce piston pressure oscillations to an accepta-

ble level, the facility was operated in push-through

mode during the commissioning of the swirl generator.

In the normal mode of operation, the plug valve is

adjusted to open when the air in front of the piston

reaches the nominal run condition of the facility (4.6

bar and 444 K). To achieve these conditions in an isen-

tropic compression, the pre-compression conditions in

the piston tube are set to approximately 1 bar and 290 K

(that is ambient conditions). In this mode of operation

the opening of the plug valve causes a slight over-accel-

eration of the piston (of finite mass) which is difficult to

remove even by careful tuning of the opening speed.

This leads to oscillations in pressure equal in magnitude

to approximately 1 per cent of total pressure. In push-

through mode the plug valve opens at the same time as

cold gas is introduced behind the piston. In this mode,

oscillations are reduced almost to zero allowing survey

measurements to be conducted. This avoided the slight

over-acceleration (and subsequent oscillation) of the

piston that usually occurs during the compression

phase, and allowed almost steady venting of gas through

the test section (slow drift over time). In this mode of

operation, a test pressure of 2.8 bar was chosen, and the

test gas was exhausted through the turbine at ambient

inlet temperature. A rotor speed of 7700 r/min was

required to achieve the correct non-dimensional speed.

Operating the tunnel in push-through mode

reduced piston oscillations by an order of magnitude

as shown in Fig. 20. The complete area survey was

obtained using data from 24 experimental runs of

Fig. 18 Rakes of four-hole probes

Fig. 19 Measured pressures at the four holes of aprobe showing piston oscillations encoun-tered in blow-down mode

Fig. 20 Measured pressures at the four holes of aprobe showing reduced piston oscillationsduring push-through mode





the OTRF including repeat runs: measurements were

repeated to assess repeatability. The root mean

squared difference of the repeat measurements was:

1� for the pitch angle, 0.75� for the yaw angle and

0.05 per cent of mean inlet pressure for the total pres-

sure measurements.

The results from the area survey for the measured

pitch angle (�) and the yaw angle (�) are presented in

Figs 21 and 22, respectively. The survey covered one

swirler pitch. The circular dots indicate the points at

which measurements were conducted and which

could be processed to pitch and yaw angle. At other

points it was not possible to reduce the data using cal-

ibration maps. For ease of visualization, the measured

results have been interpolated/extrapolated over whole

survey area and presented in Figs 23 and 24 for the

pitch and yaw angle, respectively. For the interpolated

plots, the regions nearest to the hub and casing walls

where the data could not be obtained have been filled

with the results at the nearest measured locations.

Overall, the pitch and yaw profiles are broadly similar

in form to the results of the pilot study presented in Figs

9 and 10. That is, a well defined clockwise vortex of

approximately correct pitch-wise magnitude is formed.

The corresponding flow vectors, obtained using

the secondary flow velocity components at each

measurement point, are shown in Fig. 25. Again to aid

visualization, data has been interpolated for the internal

points and extrapolated for the points at 10 and

90 per cent span. The thick arrows represent the mea-

sured locations in the plot. The flow vectors allow visu-

alization of the clockwise vortex. The general form is

similar to that measured in the pilot study (Fig. 12).

Fig. 21 Measured pitch angle profile in the OTRF

Fig. 22 Measured yaw angle profile in the OTRF

Fig. 23 Measured pitch angle profile in the OTRFinterpolated/extrapolated over survey area

Fig. 24 Measured yaw angle profile in the OTRF inter-polated/extrapolated over survey area

Fig. 25 Secondary flow vectors profile; measured inOTRF





The yaw angle profile measured in the OTRF is

compared with the distribution from the pilot study

in Fig. 26. The target profile is also presented. Results

are presented at 20 per cent and 80 per cent span. The

measured peak yaw magnitude (approximately 50�) is

similar in the ORTF and pilot study results, but in the

OTRF there is a broader and flatter distribution of

swirl in the circumferential direction. In experimental

results from both the OTRF and the pilot study, the

peak in yaw is greater than in the target profile, but

there is good symmetry in both the circumferential

and radial directions indicating a well-formed vortex

in both experiments.

8 INLET TOTAL PRESSURE AND

TEMPERATURE WITH SWIRL

To ensure accurate comparisons between measure-

ments with and without inlet swirl, it was necessary to

characterize the total pressure loss characteristics of

the swirl module, and the effect on the inlet temper-

ature profile.

To measure the total pressure profile in the highly

whirling flow at the turbine inlet plane, four-hole

probes were used instead of pitot probes. The inlet

total pressure profile was obtained from the four-hole

probe measurements performed in the push-through

mode of operation as piston oscillations during the

normal operating mode of the facility prevented total

pressure surveys under normal run conditions. The

measured non-dimensional pressure profile is pre-

sented in Fig. 27. For ease of visualization, the mea-

sured results have been interpolated/extrapolated

over whole survey area (as discussed before) and are

presented in Fig. 28.

A variation of�1.5 per cent from the nominal mass-

mean value was observed with inlet swirl. The total

pressure was lowest at the centre of the vortex (as

might be expected due to the overturning of low-

momentum fluid) and high near the hub. It is noted

that the measurements in the OTRF are in a region of

very low dynamic head (about 0.7 per cent of the total

pressure), and therefore the total pressure variation is

significantly affected by the static pressure variation:

low static pressure is also expected at the vortex

centre. A similar trend was observed in the pilot

study measurements.

The total pressure loss across the swirl system in

the normal running condition of the OTRF could be

determined using the four-hole probe area survey

data and the total pressure measurement obtained

upstream of the swirl system: the mass-averaged

loss was approximately 2 per cent of the inlet total

pressure (estimated uncertainty 10 per cent in pres-

sure loss, which is 0.2 per cent of total pressure). This

correction allows the turbine inlet total pressure

to be determined to an accuracy of approximately

0.2 per cent from the total pressure upstream of the

swirler plate, which is measured during each run.

Fig. 26 Yaw angle profile at 20% and 80% span; com-parison of measurements in the OTRF and thepilot study with the target profile

Fig. 27 HP turbine normalized measured inlet totalpressure profile with swirl

Fig. 28 HP turbine normalized inlet total pressureprofile with swirl interpolated/extrapolatedover survey area





To evaluate HP turbine efficiency, it is necessary to

know the inlet enthalpy flux (temperature) to a high

degree of accuracy. The inlet total temperature survey

was performed over 1 swirler pitch in the normal

(blow-down) mode of operation, with nominal inlet

conditions given in Table 1.

The survey was conducted with and without inlet

swirl. Three radial rakes, each with 9 k-type 25.4 mm

bare bead thermocouples, were used to obtain mea-

surements at 19 locations in the circumferential

direction (171 measurement points). The inlet total

temperature profile obtained over 1 swirler pitch

(2 NGV pitches) with inlet swirl is presented in

Fig. 29. No significant variation from the nominal

uniform inlet condition (444 K) was observed.

9 NGV ISENTROPIC MACH NO. WITH INLET

SWIRL

To investigate the effect of inlet swirl on the aerody-

namic characteristics of the HP vane, the static pres-

sure distribution was measured with and without

inlet swirl at 10 per cent, 50 per cent, and

90 per cent spans. The pneumatic tappings used for

the measurements were distributed over a set of

vanes to achieve a good resolution of data at each

span. A comparison of the measured HP vane isen-

tropic Mach number distribution from experiments

at 10 per cent and 90 per cent span is presented in

Figs 30 and 31, respectively, with and without inlet

swirl. The predictions obtained from CFD computa-

tions for both cases are also presented.

The effect of inlet swirl on the HP vane aerodynam-

ics is significant. The clockwise inlet vortex (as viewed

from upstream) results into an increase in incidence

angle at 10 per cent radial span and therefore an

increase in the aerodynamic loading. At 90 per cent

span, there is negative incidence and a reduction in

the aerodynamic loading. Negative incidence causes

a region of diffusion on the pressure surface between

approximately 4 per cent and 25 per cent axial chord.

Such significant variations in loading distribution

would be expected to impact the stage efficiency,

and the heat transfer characteristics of the stage.

This will be the focus of future work.

10 CONCLUSION

The use of aggressive swirl in modern lean-burn com-

bustors can result in high residual swirl at combustor

exit, which may have a considerable effect on the

aerodynamic and heat transfer characteristics of the

HP turbine. In order to investigate these effects, a

combustor swirl simulator has been designed and

developed that is suitable for use in transient turbine

test facilities. The swirl simulator was successfully

installed and commissioned in a full-scale, short-

duration, transonic turbine test facility. The mea-

sured swirl profile was similar to the target profile,

and is representative of the high-swirl conditions in

modern low-NOx combustors. The design, develop-

ment, and commissioning of the swirl simulator have

been presented in this article.

Aerodynamic measurements on the HP NGV sur-

face at 10 per cent and 90 per cent span have also

Fig. 29 HP turbine inlet total temperature profile withinlet swirl Fig. 30 NGV isentropic Mach number at 10% span

Fig. 31 NGV isentropic Mach number at 90% span





been discussed. The comparison of isentropic Mach

number with and without swirl at these span loca-

tions highlights the significant impact of swirl on

the loading distribution of the vane. This is caused

by increased flow incidence with inlet swirl near the

hub, and reduced incidence near the casing.

It is clear that high levels of inlet swirl cause sig-

nificant changes in vane flow field, which may persist,

to a lesser extent, through the rotor. The detailed

analysis of the effects of swirl on the secondary

flows, loss characteristic and heat transfer of the HP

turbine vane and rotor is the subject of near-future

research.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the financial

support provided by the European Commission to

the TATEF-II project: Turbine Aero-Thermal

External Flows. The technical assistance of David

O’Dell, Dominic Harris, and David Cardwell is also

acknowledged.

� Authors 2011

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APPENDIX

Notation

C� yaw coefficient

C� pitch coefficient

CT total pressure coefficient

CD dynamic pressure coefficient

N� ffiffiffiffi

Tp

(pseudo) non-dimensional speed

p pressure

pD dynamic pressure

pmin minimum of the four hole pressures

T temperature

Tg/Tw gas-to-wall temperature ratio

u, U velocity

� yaw angle

� pitch angle

� density

! turbine speed (r/min)

Subscripts

a, b, c, d holes of probe (Fig. 5)

0 total (absolute)

1 NGV inlet plane

2 NGV exit plane

Acronyms

HP high pressure

M Mach number

Re Reynolds number

TTF turbine test facility

Tu turbulence intensity





a combustor-representative swirl simulator for a transonic turbine research facility

Documents