cfd jet into cross flow boundary layer controlan.pdf

8/10/2019 CFD Jet into Cross Flow Boundary Layer Controlan.pdf

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American Institute of Aeronautics and Astronautics

1

Jet into Cross Flow Boundary Layer Control-

an Innovation in Gas Turbine Blade Cooling

1,2Javadi, Kh.*, 1,2 Taeibi-Rahni, M., and 1Darbandi, M.,

1- Sharif University of Technology,P. O. Box, 11365-8639, Tehran, Iran.

2- Aerospace Research Institute, (Ministry of Science, Research, and Technology), P.O. Box 15875-3885,

Tehran, Iran

New standpoint of turbulent coolant jets into crossflow, which have numerous applications

in traditional and modern technology, especially in gas turbine blades, is presented in this

work. It is more than half a century that, many researchers have been studying jet into cross

flow to understand its behavior and to predict and control it better. Previous studies indicate

that, the main attentions had been on: a- geometrical parameters such as: inclined andcompound jet angles, holes shape, jets array arrangements, jets spacing, and jets channel

depth, b- flow characteristics like: blowing ratio, density ratio, jet and cross flow Reynolds

numbers, and turbulence intensity. Here, we have looked at this problem from different

viewpoints and have introduced a new approach to control the jet and the cross flow

interactions. In this approach, two smaller coolant jets have been installed at both sides in

front of the main coolant jet. The main purposes of these two new jets are controlling the jet

and the cross flow interactions and to reduce the mixing strength between them through new

interactions between the counter rotating vortex pairs. Our numerical scheme was based on

finite volume pressure based SIMPLE- method using a non-uniform staggered grid. On the

other hand, the Reynolds stress transport model was used to close the incompressible

Reynolds averaged Navier-Stocks (RANS) equations. Our results show that, this new

approach at least has four significant improvements; 1- a significant enhancement in the film

cooling effectiveness (about 50%), 2- a considerable improvement in uniformity distributionof the coolant film over the plate, 3- reduction of mixing strength between the hot free

stream and the coolant jets, and 4- skin friction drag reduction. Note; in order for the results

of this new approach to be comparable with the ones from traditionally film cooling

methods, the total coolant air and the cross sections of the newcombined triple-jetshave been

taken to be the same as the ordinary one.

*PhD Student at Aerospace Engineering Department, Sharif University of Technology, E-mail, [email protected].

Associate Prof. at Aerospace Engineering Department, Sharif University of Technology, E-mail, [email protected]

Associate Prof. at Aerospace Engineering Department, Sharif University of Technology, E-mail, [email protected].

35th AIAA Fluid Dynamics Conference and Exhibit6 - 9 June 2005, Toronto, Ontario Canada

AIAA 2005-527

Copyright 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


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Nomenclature

a = Speed of Sound iu = Fluctuative Velocity Components

1C , 2C , & C = Empirical Constants in RSM Model Vcf = Cross Flow Velocity

C2, C1 , & sC = Empirical Constants in RSM Model jiij uu = = Reynolds Stress Tensor

ijC = Convection Terms in RSM Model

cfjet

cfaw

TT

TT

=

= Film Cooling Effectiveness

D = Jet Hydraulic Diameterk

kx = Component of the Unit Normal to

= the Wall

d = Normal Distance from the Wall = Viscosity

LijD

= Molecular Diffusion Terms in RSM

Model

k , , & 2 = Empirical Constants in SST

Model

TijD = Turbulent Diffusion Terms in RSM

Model , * , & = Empirical Constants in SST

Model

1F and 2F = Switching Functions in ( )Model k = Prandtl Number

ijF = Production Terms by System Rotation = Density

ijG = Buoyancy Terms = A Dependent Variable

J = Momentum Ratio; )/()(22

cfcfjetjet VV ij = Pressure Strain Terms in RSM

Model

k = Turbulence Kinetic Energy 1,ij = Slow Pressure-Strain Terms in

RSM Model

tM = Turbulent Mach Number 2,ij = Rapid Pressure-Strain Terms in

RSM model

ijP = Production Terms in RSM Model 3,ij

= Wall-Reflection Terms in RSM

Model

cfjet VVR /= = Jet-to-Cross Flow Velocity Ratio = Turbulence Energy Dissipation

Rate

,U ,V &

W

= Mean Velocity Components ij = Rare of Dissipation Terms

iU = Mean Velocity Components = Specific Dissipation Rate

( )k*

/

iU = Instantaneous Velocity Components t = Eddy Kinematics Viscosity

( )cf = Designates Cross Flow


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5) Jet Holes Spacing [42, 51],

The spanwise jet spacing, S/D, (where S is spanwise jet spacing and D is the jet hydraulic diameter) is very

important. A common value for S/D is three. Larger values can not full protect the surface and smaller values

cause structural limitations.

6) Jet Array Arrangements- Single or Double Rows Effects[33, 38, 39, 52-59]The most important keys to protect the surfaces from the high temperature hot gas are jets coolant location and

their arrangements over the surface. For the same hole geometry, compound angle orientation, inclined angle

injection, and blowing ratio, a staggered arrangement of jet arrays have higher total film cooling effectivenesswith respect to the regular (inline) jet arrays. This is because; staggered arrangements can help the jets to recover

for each other. Thus, for the same coolant hole effectiveness, a staggered arrangement will improve total surface

effectiveness significantly.

7) Jet and Cross flow Reynolds Numbers [36, 41]Both the jet and the cross flow Reynolds numbers can strongly affect the characteristics length, velocity, and

time scales of the flow, e.g. the characteristics of the separation and the size of eddies are affected by both

Reynolds numbers. Not, jets into cross flow interactions are a multi length, velocity, and time scales

phenomenon.

8) Jet and Cross Flow Turbulence Intensity [41, 47, 62- 64]The turbulence intensity affects the mixing of the coolant jet and the main hot cross flow process. Hence higher

turbulence intensity leads to stronger mixing of the coolant jet and that of the hot cross flow. This is not suitablefrom film cooling point of view.

9) Density Ratio [30-32, 36, 44, 60, 61]For the same blowing ratio, increasing of density ratio will improve cooling effectiveness.

10) Compressibility Effects and Shock Waves Interaction.

A careful review on literature indicates that, almost all of the researchers attentions are to improve film

cooling effectiveness through geometrical parameters (injection angle, hole shape, jet array, their position, etc.) and

flow characteristics (Reynolds number, blowing ratio, turbulence intensity, density ratio, etc.). In this work we have

looked at this problem from different point of view and have succeeded to innovate a new approach to control thequality of the interactions and eventually to improve film cooling effectiveness with increasing coolant film

uniformity. The basis of this idea goes back to our previous studies on film cooling [ 65, 66], where the significant

role of mixing zones in destroying the coolant film was obviously observed. In this innovation, controlling of the jetinto cross flow interactions is our main objective. For this purpose, two smaller coolant jets are considered on both

front sides of the main coolant jet. The main goal of installing these two smaller coolant jets is to control the

interactions and to reduce the mixing strength between the coolant jets and the hot free stream. Using this newapproach has many advantages such as: 1- the improvement of film cooling, 2- the improvement of the uniformity ofthe coolant jets distribution, 3- the reduction of mixing strength between the hot free stream and the coolant jets

(which increases the stability and the steadiness of the coolant effects downstream of the injection), and 4- skin

friction drag reduction.

II. Governing Equation

The governing equations are Reynolds averaged Navier-Stoks (RANS) equation conservation of mass,

momentum, and energy for a stationary turbulent incompressible flow as follow:The conservation of mass stats that:

(1)0=

i

i

x

U

,

while the conservation of linear momentum is:

(2)

+

+

=

i

j

j

i

jij

i

jx

U

x

U

xx

p

x

UU )( ji

j

uux

+ ,


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and the conservation of energy is:

(3)

)})PrPr

{()(jt

t

l

l

j

j

j x

T

xTU

x

+

=

wherejiuu are the Reynolds stress terms, which need to be modeled. Since, our problem is multiple

characteristic scales eddy viscosity models are not very suitable to employ. Thus, Reynolds stress models (RSM)which have higher potential to simulate complex flows, have been used. Also, SST (k-/k-) turbulence model wasused for calculating the turbulent diffusivity in the Reynolds stress transport equation.

The (RSM) Equations are:

(5)

( ) ( )=

+

jik

k

ji uuUx

uut

( )[ ]+++

jikikjkji

k

uupuuux

( )

ji

kk

uuxx

+

k

i

kj

k

j

kix

Uuu

x

Uuu

+

+

i

j

j

i

x

u

x

up

k

j

k

i

x

u

x

u

2 ( )jkmmiikmmjk uuuu + 2 ,

While the SST Equations:

(6)

( )

+

+

=j

tk

jj

iij

x

k

xk

x

U

Dt

kD

* ( )jj xx

kF

+

1112 2

(7)

( )

+

+

=

j

t

jj

i

ij

t xxx

U

Dt

D

2 .

More details of the terms and constants are represented in [21, 22].

III. Computational Methodology

A FORTRAN computer program was developed to solve a three-dimensional, turbulent, incompressible, andtime averaged Navier-Stocks equations. Reynolds stress turbulent model incorporated with SST model was used to

overcome the closure problem. The numerical method used was finite volume method a employing hybrid scheme

over a non-uniform, structured, and staggered grid. The continuity and the momentum equations were linked via the

pressure based SIMPLE algorithms. Other equations such as the turbulent kinetic energy and its dissipation ratesequations were solved segregately. Finally, a line by line three diagonal matrix algorithm (TDMA) was used to solve

the discretized algebraic equations with appropriate under-relaxation factor to speed up the convergence.

IV. Physical Domain and Boundary Conditions

The physical domain and the boundary condition used are described in this section. Of course, we have different

domain depending on the ordinary or new film cooling approach used in this work. The boundary conditions on the

other hand are broken into inlet, outlet, no flux, periodic, and solid wall.

A. Ordinary Film Cooling Physical Domain

The results of our new approach were compared with a basic fundamental squared jet normally injected into a

cross flow (fig. 1),which is based on Ajersch et. als experimental (LDV) and numerical (k-) works [14]. Their jet

hydraulic diameter (jet width, D) was 12.7mm and their jet Reynolds number based on D was 4700 with a fixedvelocity speed of 5.5 m/s at the entrance of the jet channel. They tried three blowing ratios (R) of 0.5, 1, and 1.5.

However, we used R=0.5, which is more common in film cooling. our computational domain was non-dimensionalized respect to D, so that, the jet channel lengths is 5D and the cross flow region is extended from 5D


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upstream of the center of the jet to 40D downstream. In the vertical direction, the domain extends to 20D above the

flat plate.

B. New Film Cooling Approach Physical Domain

In our new approach, two smaller jets have been considered in both sides in front of the main jet. Note, from filmcooling point of view, in order for the results of this new approach to be comparable with the traditionally film

cooling approach, the same amount of total coolant air and the same total cross sectional area have been used (Fig.

2). Other parameters such as the lengths of physical domain, inlet jet and cross flow velocities (blowing ratio), etc.are the same as traditional film cooling case. However, jet Reynolds number would be different.

C. Boundary ConditionsIn this work, five types of boundary conditions namely: inlet, outlet, no-flux, solid wall, and periodic (Fig. 1)

were used as follows:

1) Inlet Boundary Condition: the inlet velocities, the turbulent kinetic energy and its dissipation rate, and the

Reynolds stress terms were prescribed as in [14, 22].

2) Outlet Boundary Condition: Zero gradients of flow quantities were used at this boundary. Also, since there is nomass conservation guarantee during SIMPLE iteration, we used the following relation for the streamwise

velocity component:

)8()/(,,1,, outinKJNIKJNI MMuu &&

= ,

where inM&

and outM&

are inlet and outlet mass flow rates, respectively.

3)No-flux Boundary Condition: At infinitely far from the plate, no-flux boundary condition were used as:

)9(0=

n

,

where, n is the direction normal to the face.

4) Periodic Boundary Condition: it was assumed that there were infinite numbers of coolant injected jets inspanwaise direction. In order to consider the effects of neighboring jets, periodic boundary condition follow was

used as:

)10(1,,1,, = NKjiji ; 2,,,, jiNKji = ,

However, since we used staggered grid, the periodic condition for z velocity component is:

)11(

1,,2,, = NKjiji ww , 3,,,, jiNKji ww = .

5) Solid Wall Boundary Condition: No slip boundary condition was used at the wall [22].

V. Results and Discussions

Three-dimensional turbulent multiple jets into cross flow were computationally simulated, using finite volume

method, SIMPLE algorithm, and Reynolds stress turbulence model. For code validation purpose, we compared our

results with previous experimental [[14] and numerical [14, 21]. Also, the related grid resolution study was

performed in our previous work [22].Figures 2-5 also, show the comparisons of our results with other experimental and numerical works. As it is

obvious from these figures and also, based on discussion in our previous works [22], the abilities of RSM model for

prediction of both the mean quantities and Reynolds stress terms at different flow locations are much higher relative

to two-equation models.Generally, when a jet is injected into a cross flow, several complex physical phenomenon occur downstream of

it, particularly the counter rotating vortex pair (CRVP) which is generated just behind the jet and moves

downstream. The CRVP strength and its influence on the cross flow characteristics are highly dependent on theblowing ratio. Stronger strength leads to more jet and cross flow interactions, more penetration into the boundary

layer, and higher mixing between the coolant jets and the hot cross flow. However, this is not suitable from film

cooling point of view. To improve cooling effectiveness all previous works were focused on the geometrical and

flow characteristics parameters of the jet the cross flow (as mentioned before).

In this work, we have introduced a new approach to control the interactions between the jet and the cross flow inorder to reduce fluid mixing and eventually to improve film cooling effectiveness. We have examined several


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technique to achieve this goal, e.g., combining of suction/blowing jets [66]. In our final selection, two small coolant

jets are considered at both sides of the main coolant jet and formcombined-blowing triple-jets units.this technique

has mainly four significant effects, including: 1- drastic mixing reduction between the coolant jets and the hot cross

flow, 2-considerable film cooling enhancement, 3- significant improvement of the coolant film distribution, which

leads to more uniform cooled surfaces, and 4- noticeable skin friction drag reduction. Here, we are going to discusshow this new system works so well. Note, this work is a fundamental study to introduce this new approach for

controlling the mixing of a jet into a cross flow, particularly to improve film cooling effectiveness and thus, more

work needs to be done to optimize it. Our research teams are presently working on the effects of different jetgeometry and flow characteristics on this new approach.

1) Mixing Reduction between the Coolant Jets and the Main Hot Free StreamAs mentioned earlier, when a jet is injected into a cross flow, a counter rotating vortex pair (CRVP) will be

created after the jet and moves downstream in a helical fashion. This phenomenon also occurs for the two small jets

of our new approach. In other word, two weaker CRVPs will be created at both side of the main coolant jet, one at

the left and one at the right. Note, the vortical field generated by the main coolant jet and the two small jets interact

with each other, while the direction of their rotation are opposite to each other. In other words, as Fig. 6shows, theright mate of the CRVP generated by the left jet, interacts with the left mate of CRVP generated by the main jet and

vice versa. Note, from Fig. 6it is clear that, in the ordinary case, the vortices of the CRVP have opposite directions.

However, they can not weaken each other since they have the same direction at their contact points. Hence they cannot destroy each other after meeting. While, if we pay more attention to this figure, we will see that, at the contact

points between vortexes of the main jet and that of tow new small jets the vortices have opposite directions and thusweaken of their strength occurs in our new approach. The interactions of the vortexes, which are on the contraryrotating directions at meeting interface is the key to our new approach.In this situation, the interacted vortices will

weaken each other after meeting. Therefore, the strength of the CRVP created by the main coolant jet will be

decreased. Figures 6-aand 6-b compare the structure and the strength of the main CRVP without and with small

jets. It is clear from this figure how the CRVPs of two small coolant jets and main jet interacts and causes the

breakdown of their strength. This leads to less interaction with hot cross flow and less mixing between the coolant

jet and the hot cross flow. The reduction of the mixing strength between the hot free stream and the coolant jetscause enhancement of the stability and the steadiness of the coolant effects downstream of the coolant jet injections.

It is necessary to emphasize here that, our new technique is quite different from double rows staggered holes, which

are widely used in film cooling applications. In the staggered row approaches, there are not very strong interactionsbetween the neighboring vortices. The main goal of the staggered rows is to improve film cooling effectiveness by

overlapping of the coolant jets to improve uniform film cooling distribution, not reduction of hot and cold mixing

interactions.2) Considerable Improvement on Film Cooling Effectiveness

The injection of the coolant jet into cross flow makes a low pressure region just behind the jet. Since, this low

pressure region can not be void of fluid; hot gases flow into this region and produce a layer of hot gases under the

coolant jet and decrease the efficiency of film cooling. Figure 7-ashows this phenomenon schematically (up) and

numerically (down). The main goal of our new approach is to avoid the arrival of these hot gases into this region.Several techniques were examined [65, 66] and finally the most efficient one, (combined triple-jets units) were

obtained. Fig. 7-b shows this schematically (up) and numerically (down). If we compare Figs. 7-a and 7-b, we note

how these new small jets divert the hot gases. In this situation, the coolant jet fills in the region behind the jet isteadof the hot gases. This is the first main reason for improvement of film cooling in our new approach. Also, note from

Fig. 7-a again that, during the rotation of the CRVP generated by the main coolant jet (ordinary film cooling) the hot

gases comedown towards the surface continuously and dos not permit the coolant film to cool down surfaces well

enough. While, in our new technique, the interactions between the vortical fields generated by the main and the

small jets like a fluid barrier prevent the penetration of the hot gases towards the surface (see Fig. 8). This is thesecond reason for improving the film cooling effectiveness in our new approach.

Fig. 9illustrates the velocity vector field at x-y center plane. This figure compares the coolant jets penetration

into the boundary layer of the hot cross flow for the combined triple-jets (this work) and ordinary film cooling

techniques. As it is clear from this figure, the influence of jet into the boundary layer for our new approach is lessthan that of the ordinary film cooling. This is the third reason for improving film cooling effectiveness by our new

approach. Figure 10 compares the film cooling effectiveness for our new approach and a common ordinary filmcooling. As this figure shows, there exists a considerable improvement of the film cooling effectiveness (about 50%)

in our new approach.


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3) Significant Improvement on Film Cooling Distribution

Having more uniform film cooling distribution is also very important, especially from thermal stress point of

view. One of the advantages of the staggered rows (compared to inline rows) is that, for the same hole,

characteristics, the total uniformity of the staggered holes is higher than that of the inline holes because of the

overlapping of the coolant film distribution. The existence of two small coolant jets at both sides in front of the mainjet, which makes a unit of combine triple-coolant jet with respect to one unit of ordinary film cooling (inline or

staggered), leads to the more uniform coolant film distribution. Also, because of less interaction between the main

stream and the coolant jets in our new approach, this uniformity continues the region way downstream of the jet.Figures 11-a and 11-b compare the cooling effectiveness distribution over the surface in our new approach and in an

ordinary film cooling. From this figure, one can note that, a significant improvement on the coolant film distribution

is obtained in our new approach. It should be emphasized again that, this technique must not to be mistaken with thestaggered rows approach. To correct comparison, the uniformity of one unit of these combined triple-jetsmust be

compared with the uniformity of one hole of any staggered or inline rows. Note, these units of combined triple-jets

can be arranged in a staggered or inline form.

4) Enhancement of Skin Friction Drag ReductionAlthough many studies have been performed on the jet into cross flow, but few researches have studied the relatedfriction drag phenomenon. In our study, we have compared the skin friction drag coefficient in our new (combined

triple-jets) and in the ordinary approaches [67]. Obviously, the skin friction drag is directly related to the shear

stresses on the wall (thus, velocity gradients at the wall). Hence, we need to look at the velocity profiles at the wallwith and without the coolant jets injections. Our results show that, generally, when a jet is injected into a cross flow,

the skin friction drag is decreased. This is because, by injecting a jet into the boundary layer of a turbulent crossflow, the velocity profile, which has high gradient near the wall will be distorted by the coolant jet and new velocity

profiles will be generated. These new profiles have less gradient close to the wall, particularly near the jet injection.As the flow moves downstream, the effects of the coolant jets decrease and the flow tends to have a regular profile.

Therefore, we expect an increase in the skin friction drag, as we go far away from the jet channel. The more the

turbulent boundary layer gets distorted and the more this distortion continues downstream region, the more decrease

in the skin friction drag will be achieved. Figure 12 shows the streamwise velocity profile at different location. As it

is clear from this figure, the velocity profile for thecombined triple-jetshas less gradient near the wall (except nearthe jet exit). For comparison, the velocity profile for a fully developed turbulent flow on a flat plate without any jet

injection is presented. From fig. 12,we can see that, at all locations the velocity gradient near the wall for turbulent

flow without jet injection is higher than the others. Since, the main part of the skin friction drag is due to streamwisevelocity component, then we focus on the gradient of this velocity component close to the wall. Also, since the

velocity at the wall is zero, the velocity at the first cell above the wall dividing to its distance give us the velocity

gradient at the wall. Also, since we used a structured grid, all such distances are equal. Therefore, the same strategycan be used all along the wall. Using this strategy, we can study the distribution of the velocity gradient downstream

of the jet injection easier. Figure 13demonstrates the velocity distribution at the first cells along the wall at three

different positions, namely: the center line, 0.5D and 1.D from the centerline (spanwise direction). This figure

indicates that, except for a small region near the coolant jet injection, the velocity gradient at the wall for our new

approach is considerably less than that of the ordinary film cooling. For better understanding of the roles of the twosmall jets at both sides in front of the main jet on reduction of skin friction drag, we have solved the problem

without small coolant jet, and geometry like the main coolant jet as combined triple-jet. Finally, Fig. 14compares

the skin friction drag coefficient distribution along the streamwise direction which has been spanwized averaged. Asit is obvious from this figure, the skin friction drag coefficient in our new approach (combined triple-jet) is about

20% less than the ordinary film cooling. More details of this topic have been presented in [67].

VI. ConclusionIn this work, a new approach to control jet into cross flow interactions was introduced, in which two small

coolant jets were installed at both sides in front of the main coolant jet. Interactions between the new CRVPs

generated by small jets, and the CRVP generated by the main coolant jet considerably reduce the mixing strength of

the coolant jets with the hot cross flow. In order for the results of this new approach to be comparable with the ones

from the traditionally film cooling methods, the total coolant air and the cross sections of the new combined triple-

jetshave been taken to be the same. Our results indicate that, our new approach has at least four significant effects

as:


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1) Mixing Reduction between the Coolant Jets and the Main Hot Free Stream: the new interactions between the

weaker CRVPs created by the small jets at both side of the main hole, and the CRVP generated by the main

coolant jet weaken their strengths. Theinteraction between the vortexes of opposite sings when touching eachother at the contact points is the key of our new combined triple-jets approach. The reduction of mixing

strength between the hot free stream and the coolant jets increases the stability and steadiness of coolant effectsdownstream of the injection jets. It is necessary to emphasize that, this technique is quite different from double

rows staggered holes which is widely used in film cooling. In the staggered cases, there are not strong

interactions between neighboring vortices. The main goal of staggered rows is to improve film coolingeffectiveness by overlapping the effecetcs and help uniform.

2) Significant Improvement of the Film Cooling Effectiveness (about 50%): Installing two small new jets at

both sides in front of the main coolant jet will divert the hot cross flow and thus, does not permit it to flow intothe low pressure region behind the main coolant jet. In this situation, this is the coolant jet which fills in this

region (not the hot cross flow). Also, in our new combined triple-jetstechnique, the interactions between the

CRVPs generated by the main and the small coolant jets like a fluid barrier prevent the displacement of the hot

gases towards the surface.

3) Significant Improvement of the Coolant Film Distribution: The existences of two small coolant jets causemore uniform coolant film distribution. Because of the mixing reduction between the main stream and the

coolant jets, this uniformity extends to downstream. In combined triple-jetssystem it seems that, not only the

interactions between the new weak CRVPs and the main strong CRVP arent undesirable, but also they areuseful for accomplishing a desirable momentum and energy transport in spanwise, leading to a more uniform

coolant film distribution in that direction as well.4) Enhancement of Skin Friction Drag Reduction: Generally, when a jet is injected into a turbulent cross flow, it

disturbs the cross flow turbulent boundary layer and thus the skin friction drag will be decreased. The more the

amount of boundary layer disturbance and the more the steadiness of this disturbance along the streawise

direction, the more the skin friction drag reduction. Our results show that, in our combined triple-jetsunits the

skin friction drag reduction is about 20% higher.

It should be noted that, this work is a fundamental study to introduce this new approach for controlling the

mixing of a jet into a cross flow, particularly to improve film cooling effectiveness. Surely, more work needs tobe done to optimize it. Our research teams are presently working on the effects of different jet geometry and

flow characteristics on this new approach.

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17Hassan I., Findlay, M., Salcudean, M., and Gartshore,I. (1998) Prediction of Film Cooling with Compountd- Angle Injection

Using Different Turbulence Models, CFD 98,pp.1-6.18Medic G. and Durbin P., (2002) Toward Improved Prediction of Heat Transfer on Turbine Blades, Journal of

Turbomachinery, Vol. 124, pp. 187-191.19Medic G. and Durbin P., (2002) Toward Improved Film Cooling Prediction, Journal of Turbomachinery, Vol. 124, No. 193.20

Chochua, G., Shyy, W., Thakur, S., Brankovic, A., Lieneau, J., Porter, L. and Lischinsky, D., (2000) "A Computational andExperimental Investigation of turbulent Jet and Crossflow Interaction," Numerical Heat Transfer, Vol. 38, pp. 557-572.21Keimasi, M. R. and Taeibi-Rahni, M., (2001) Numerical Simulation of Jets in a cross flow Using Different Turbulence

Models, AIAA J., Vol. 39, No. 12, pp. 2268-2277.22Javadi, A., Javadi, K., Taeibi-Rahni M., and Keimasi M., (2002) Reynolds Stress Turbulence Models for Prediction of Shear

Stress Terms in Cross Flow Film Cooling Numerical Simulation, 4th International ASME/JSME/KSME Symposium oncomputational technology CFD) for fluid/thermal/chemical/stress systems and industrial application, Hyatt Regency, Vancouver,

CANADA.23Thevenin, J., Amaral, M., Malvos, H., and Mauillon, L., (1998) Computation of a Three-Dimensional Swirling Jet into a

Crossflow Using a Reynolds Stress Turbulence Model, ECCOMAS98.24

Fu, S., Launder, B.E., and Leschziner, M.A., (1987) Modeling Strongly Swirling Recirculating Jet Flow with Reynolds-StressTransport Closures, Sixth Symposium on Turbulent Shear Flows, Toulouse, France.

25Ince, N.Z. and Leschziner, M.A., (1990) Calculation of Single and Multiple Jets in Cross Flow with and without Impingement

Using Second-Moment Closure, Eng. Turbulence modeling and Experiments, Elsevier, pp. 143.26

Tyagi, M. and Acharya, S., (1999) Large eddy simulation of Jets in Crossflow: Free stream Turbulence Effects, FEDSM 99-

7799, 3rd

ASME/JSME Joint Fluid Engineering Conference.27Ramezani-Zadeh, M. and Taeibi-Rahni, M., (2001) Large Eddy Simulation of Multiple Jets in a Cross Flow Using

Smagorinsky Model, ISME 2001, pp. 293-299, Guilan University, Rasht-Iran.28

Ramezani-Zadeh, M., Saidi, M.H., and Taeibi-Rahni, M., (2004) Large Eddy Simulation of Density Ratio Effects on Two-Dimensional Film Cooling, 2ndBSME-ASME Int. Conference n Thermal Engineering, Dhaka, Bangladesh, Vol. 2, pp. 659-665.

29Eckert, E.R.G. and Livingood, J.N.B. (1954) Comparison of Effectiveness of Convection, Transpiration, and Film-Cooling

Methods with Air as Coolant, NASA-Report-1182.

30Bladauf, S., Schulz, A., and Witting, S., (2001) High-Resolution Measurements of Local Heat Transfer Coefficients From

Discrete Hole Film Cooling, Journal of Turbomachinery, Vol. 123.31

Goldstein, R.J., Jin, P., and Olson, R.L., (1999) Film Cooling Effectiveness and Mass/Heat Transfer Coefficient Downstreamof one Row of Discrete Holes, Journal of Turbomachinery, Vol.121 p.225-232.

32Bell, C.M., Hamakawa, H., and Ligrani, P.M., (2000) Film Cooling From Shaped Holes, ASME J., Vol. 122.33

Ahn J., Jung, I.S. and Lee J.S., (2003) Film Cooling from Two Rows of Holes with Opposite Orientation Angle: InjectantBehavior and Adiabatic Film Cooling Effectiveness, Int. J. Heat and Fluid Flow Vol. 24.

34

Chang, Y.R. and Chen, K.S., (1995) Prediction of Opposing turbulent Line Jets Discharged Laterally into ConfinedCrossflow, Int. J. Heat Mass Transfer, Vol. 38 No. 9.

35Bridges A. and Smith D. R., (2003) Influence of Orifice Orientation on the Synthetic Jet-boundary-layer Interaction, AIAA J.

Vol. 41, No. 12.36 McGrath, L.E. and Leylek J.H., (1999) Physics of Hot Crossflow Ingestion in Film Cooling, ASME J., Vol. 121.37Goldstein, R.J. and Stone, L.D., (1997) Row-of-Holes Film Cooling of Curved Walls at Low Injection Angle, Transactions

of ASME, Vol. 119,pp.574-57938Azzi, A., Abidat, M., Jubran, B.A., and Theodoridis, G.S., (2001) "Film Cooling Predictions of Simple and Compound Angle

Injection from One and Two Staggered Rows," Numerical Heat Transfer, Part A., Vol. 40, pp. 1-23.39Jubran, B.A. and Maiteh, B.Y., (1999)" Film Cooling and Heat Transfer from a Combination of Two Rows of Simple and/or

Compound Angle Holes in Inline and/or Staggered Configurations," Journal of Heat and Mass Transfer, Vol. 34, No 6, 495-502.40Gartshore, I. and Salcudean, M., (2001) Film Cooling Injection Hole geometry: Hole Shape Comparison for Compound

Cooling Orientation, AIAA J., Vol. 39, No. 8, pp-1493-1499.41Rowbury D.A., Oldfield M.L.G., and Lock G.D., (2001) a Method for Correlating the Influence of External Crossflow on the

Discharge Coefficient of Film Cooling Holes, ASME J., Vol. 123.

42Holdeman, J.D. and Walker, R.E. (1977) Mixing of a Row of Jets with a Confined Crossflow, AIAA J., Vol. 15, No. 2, pp.243-249.

43Teng, S. and Han, Je-C., (2001) Effect of Film-Hole Shape on Turbine-Blade Heat-Transfer Coefficient Distribution, Journal

of Thermophysics and Heat Transfer, Vol. 15, No. 3.44Goldstein, R.J., Eckert, E.R. G., and Burggraf, F., (1973) Effects of Hole Geometry and Density on Three-Dimensional Film

Cooling, Int. J. Heat Mass transfer, Vol. 17, pp. 595-607.45

Hyung, H.C., Seung, G.K., and Dong, H.R., (2001) Heat/Mass Transfer Measurement within a Film Cooling Hole of Squareand Rectangular Cross Section, ASME, Vol. 123.

46Friedrichs, S., Hodson, H.P., and Dawes, W.N., (1999) the Design of an Improved End Wall Film-Cooling Configuration,ASME, Journal of Turbomachinery, Vol. 121, pp. 772-780.


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47Burd, S.W., Kaszeta, R.W., and Simon, T.W., (1998) Measurements in Film Cooling Flows: Hole L/D and Turbulenceintensity, Journal of Turbumachinary, Vol. 120, No. 4, pp. 791-798

48Walters, D.K. and Leylek, J.H. (1997) a Systematic Computational Methodology Applied to a Three-Dimensional Film

Cooling Flow Field, ASME J. Turbomachinery, Vol. 119, pp.777-785.49Seo, H.J., Lee, J.S. and Ligrani, P.M., (1998) the Effect of Injection Hole Length on Film Cooling with Bulk Flow

Pulsations, International Journal of Heat and Mass Transfer, Vol. 41.50Azzi, A. and Jubran, B. A., (2003), Numerical Modeling of Film Cooling from Short Length Stream-Wise Injection Holes, J.

Heat and Mass Transfer, Vol. 39.51Sterland, P.R. and Hollingsworth, M.A., (1975), an Experimental Study of Multiple Jets Directed Normally to a Cross-Flow,Journal of Mechanical Engineering Science, Vol. 17, No. 3.

52Ligrani, P.M., Ciriello, S., and Bishop. D.T. (1992) Heat Transfer, Adiabatic Effectiveness, and Injectant DistributionsDownstream of a; Single Row and two Staggered Rows of Compound Angle Film Cooling Holes, ASME J. Turbomachinery, Vol.114, pp. 687-700.

53Ligrani, P.M., Wigle, J.M., Ciriello, S., and Jackson, S.W., (1994) "Film-Cooling From Holes with Compound Angle

Orientations: Part 1-Results Downstream of Two Staggered Rows of Holes with 3d Spanwise Spacing," ASME Journal of HeatTransfer, Vol. 116, pp. 341-352.

54Ligrani, P.M. and Ramsey, A.E., (1997) Film Cooling from Spaswise-Orinted Holes in Two Staggered Rows, ASME J.

Turbomachinery, Vol. 119, pp. 562-567.55Dittmar, J., Schulz, A., and Wittig, S., (2004) Adiabatic Effectiveness and Heat Transfer Coefficient of Shaped Film Cooling

Holes on a Scaled Guide Vane Pressure Side Model, International Journal of Rotating Machinery, Vol. 10, No.5, pp. 345354.56

Behbahani, A.I. and Goldstein, R.J., (1983) Local Heat Transfer to Staggered Arrays of Impinging Circular Air Jets, ASMEJ. of Engineering and Power, Vol. 105, pp. 354-360.

57

Florschuetz, L.W., Metzger, D.E., and Su, C.C, (1984) Heat Transfer Characteristics for Jet Array Impingement with InitialCrossflow, ASME J. of Heat Transfer Vol. 106, pp. 34-41.

58Vijay K. Garg Heat Transfer on a Film-Cooled Rotating Blade NASA/CR1999-209301

59Ekkad, S.V., Gao, L., and Hebert, R.T., (2002) Effect of Jet-to-Jet Spacing in Impingement Arrays on Heat Transfer, ASME

Paper IMECE2002-32108, New Orleans, La.

60Walters, D.K. and Leylek, J.H., (2000) Impact of Film-Cooling Jets on Turbine Aerodynamic Losses, J. Turbomachinery,

Vol. 122, pp.537-545.61Hass, W., Rodi., W., and Schonung B., (1992) the Influence of Density Difference between Hot and Coolant Gas on Film

Cooling by a Row of Holes: Prediction and Experiments, J. Turbomachinery, Vol. 114.62Mehendale, A. and Han, J., (1992) Influence of Main Stream Turbulence on Leading Edge Film Cooling Heat Transfer J.

Turbomachinery, Vol. 114 No. 10, pp. 705-715.63Kohli, A., and Bogard, D., (1998) Effects of Very High Free-Stream Turbulence on the Jet-Mainstream Interaction in a Film

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Transfer: Effect of Film Hole Row Location, ASME90-WA/HT-5, ASME Winter Annual Meeting, Dallas.65Javadi, A., Javadi, K., and Taeibi-Rahni, M., (2002) Simulation of Film Cooling in Gas Turbine Blades, Aerospace Research

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Javadi, A., Javadi, kh., Taebi-Rahni, M., Darbandi, M., Aavani, Kh., and Mahjoob, S., (2003) New Approach in Film Coolingon Gas Turbine Blades Using Combination of Suction/Blowing flows, Annual Report, Aerospace Research Inst., Ministry ofScience, Research and Technology, ARI.-82-31-FCG-4-1-1

67Javadi. Kh., Taeibi-Rahni M, and Javadi A., (2004) New Method to Control Turbulent Jet-into-CrossFlow Interaction- Skin

Friction Drag Reduction, 9th

Fluid Dynamics Conference, Shiraz University, Shiraz, Iran (in Persian).


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Figure 1-a.Computational domain in ordinary film cooling.

Figure 1-b. Our new film cooling scheme, showing new coolant small jets

besides the main coolant jet.


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CRVP and New weak VortexesCRVP

Z/D

Y/D

-1 0 1

0

1

2

Figure 6-a. High interactions between a

strong CRVP and hot cross flow in the

ordinary film cooling

Figure 6-b. New weaker vortices generated by

the small coolant jets breaking down the

vortex strengths and reducing the interactions

and mixing process of the hot and main

coolant jets

X/D

Z/D

0 1 2 3 4-2

-1

0

1

2

Figure 7-b. The small coolant jets diverting the

hot cross flow and not permitting it to flow

into the wake region, and improving the film

cooling effectiveness.

Figure 7-a. The flow of hot gases into the low

pressure region right after jet, decreasing the

film cooling effectiveness.


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15

X

Y

Z

Figure 8-b. The interactions between the small

coolant jets and main jet reducing the

interactions between coolant jets and cross flow

also prevent of the influence of hot cross flow

toward the surface (comb. Triple-jets, this work).

Figure 8-a. High interactions between the

coolant jet and the hot cross flow and the

influence of hot gases toward the surface,

decreasing film cooling effectiveness (ordinary

film cooling).

X/D

Y/D

0 2 4

-1

0

1

2

3

4

Figure. 9-a, The velocity vectors at jet center

plane, Showing high interaction and more

penetration into cross flow boundary layer

(ordinary film cooling).

X/D

Y/D

0 2 4

-1

0

1

2

3

4

Figure 9-b. The velocity vectors at jet center

plane in our new combined triple-jets

approach, less interaction between cross

flow and coolant jet and less penetration

into cross flow boundary layer.

FluidBa

rrier

Influence

ofh

otgas

toward

surface


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Figure 11-a Inappropriate cooling effectiveness and uniformity over the plate in ordinary film cooling

Figure 11-b. The combined triple-jets shows a high effectiveness and proper cooling uniformity over

the plate (with a same coolant air and total cross section of coolant hole in both systems).

Figure 10 Comparison of the film cooling effectiveness ( ) between the ordinary and our new

approach film cooling, notable enhancement (about 50%) is shown in this figure.


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Num. Falt Plate

Comb. Jets

Rect.

U/Vjet

Y/D

-0.5 0 0.5 1 1.5 2 2.50

0.2

0.4

0.6

0.8

1

Square

Num. Falt Plate

Comb. Jets

Rect.

U/Vjet

Y/D

-0.5 0 0.5 1 1.5 2 2.50

0.2

0.4

0.6

0.8

1

Square

Figure 12. Comparison of the streamwise velocity profiles at the main jet center plane and at

X/D=3, 8, 15.

X/D=3 X/D=8 X/D=15

Num. Falt Plate

Comb. Jets

Rect.

U/Vjet

Y/D

-0.5 0 0.5 1 1.5 2 2.50

0.2

0.4

0.6

0.8

1

Square

X/D

U/Vjet

0 10 20 30 40-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Square

Num. Falt Plate

Comb. Jets

Rect.

X/D

U/Vjet

0 10 20 30 40-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Square

Num. Falt Plate

Comb. Jets

Rect.

X/D

U/Vjet

0 10 20 30 40-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Square

Num. Falt Plate

Comb. Jets

Rect.

Figure 13. Comparison of the streamwise velocity gradient distributions along the

streamwise direction at different positions of Z/D=0., -0.5, and 1.5.

Theory

Comb. Jets (This Work)

Num. Flat Plate

X/D0 10 20 30

0

0.001

0.002

0.003

0.004

0.005

Rect.

Square

Figure 14. Comparisons of the averaged skin friction drag for our new combined triple-jets

approach and common geometries in the ordinary film cooling. A considerable reduction of

skin friction drag is shown from this figure in our new approach. (Note, for comparison

purpose, the results of the turbulent flow over flat plate without injection have also been

resented).

fC

cfd jet into cross flow boundary layer controlan.pdf

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