DETAILED EVALUATION OF CFD PREDICTIONS AGAINST LDA MEASUREMENTS FOR FLOW ON AN AEROFOIL A. Benyahia...

DETAILED EVALUATION OF CFD PREDICTIONS AGAINST LDA MEASUREMENTS FOR FLOW ON AN

AEROFOIL

A. Benyahia 1, E. Berton 1, D. Favier 1, C. Maresca 1, K. J. Badcock 2, G.N.Barakos 2

1 L.A.B.M., Laboratoire d’Aérodynamique et de Biomécanique du Mouvement, UMSR 2164 of CNRS and University of Méditerranée,

163 Avenue de Luminy, case 918, 13288 Marseille Cedex 09, France

2 University of Glasgow, Department of Aerospace Engineering? Glasgow G12 8QQ, U.K

• Introduction and objectives

• Experimental methodology: LDV measurements

• Numerical methodology: PMB approach

• Results and discussion

• Conclusions and prospects

Presentation Outline

• The detailed knowledge of the boundary-layer response to unsteadiness induced by oscillating models is of major interest in a wide range of aeronautical applications.

• This work concerns an experimental and numerical investigation of the unsteady boundary-layer on a NACA0012 aerofoil oscillating in pitching motion.

• The experimental part of the present study is based on the Embedded Laser Doppler Velocimetry, developed at LABM for unsteady boundary-layer investigation.

• From the numerical point of view, simulations were performed using the PMB solver developed at GU based on a RANS approach of turbulence.

Introduction and objectives


• Experimental methodology: ELDV measurements





V

(t) = 0 + cos ( t )

(b) Pitching motion

Forced unsteadiness law

model

optical fibres

pitching fore-and-aft

particules seeding tube

0,5

mU

laser source

S2 Luminy wind-tunnel-Experimental Set-up

Embedded Laser Doppler Velocimetry Method (ELDV)

• Embedded optical head linked with the model

• Reference frame linked with the moving surface

• Focal length f = 400 mm• Survey along the chord

(x direction)• Survey along the normal

(y direction)Optical fibres

Beam-expander 45¡ mirror

Measuring volume

tn

0U°

vu

ymin = 0,2 mm

ymax = 145 mm

Optical head

Oscillating model

turntable

Transmiting block

Optical fibers

PM1

Oscilloscop

BSA (Burst Spectrum Analyser)

Postprocessing:

Labview Macintosh

sensor position

IEEE

SETUP SETTINGSMEASUREMENTS

7 8 9

4

1

5

2

6

3

0 +/-.ENTER

SHIFT

1

3.95

9.318

1.00

3.00

4.00

8

0

1560

64

10.67

BSA enhanced

DANTEC

Opticalhead

U V

A and B

TIME/DIV

and DELAY TIME

POWER

A TRIGGER

VOLTS:DIV

CH 1

465 B

OSCILLOSCOPEVOLTS:DIV

CH 2

TRIGGER

Lasersource

000000000

000000000

SETUP SETTINGSMEASUREMENTS

7 8 9

4

1

5

2

6

3

0 +/-.ENTER

SHIFT

1

3.95

9.318

1.00

3.00

4.00

8

0

1560

64

10.67

BSA enhanced

DANTEC

PM2

Color separator

ELDV Acquisition

data acquisition

t

cycle n

One period

cycle n-1

U

with 1 n Nc (Nc 150)

STEP 1

tT

Data plot on one period STEP 2

Uuniquefictif cycle

cycle unique fictif

tT

Statistic threatment on each intervalSTEP 3

une des 512 cases<U>

<U>

tT

STEP 4 Périodic signal/ Fourrier analyse

256 harmonics~U

u'(t) = U(t) - U(t)~

Unsteady measurements processing

Parallel Multi-Block (PMB) : RANS approach

for the turlence

PMB RANS approach principle

0

y

GG

x

FF

t

W ii

• Transport equations

TevuW ,,,

uhuvpuuF i ,,, 2 vhpvuvuG i ,,, 2

xyyxxxyxx qvuF ,,,0Re1 yyyxyyyxy qvuG ,,,0Re

1

ky

v

x

u

x

uTxx

3

2

3

22

ky

v

x

u

y

vTyy

3

2

3

22

y

v

x

uTxy

• The resolution method

Implicite scheme : 1,,,,

,,

,,1

,, 1

nkjikji

kji

nkji

nkji WR

Vt

WW

Turbulence models: 1 or 2 equations models. Spalart-Allmaras

(SA), k- et SST.

' 'ppp 'uuu 'vvv


• Le modèle SA1

~ fT

31

3

3

1

c

f

~

2

12

21

~~~~.

1~~~

d

fccScDt

Dbb

222

~~

f

dSS

12 1

1

f

f

6

1

63

6

631

cg

cgf rrcrg 6

2 22~~

dSr

135.01 bc 32 622.02 bc 41.0 762.21 c 3.02 c 23 c 1.71 c


• Le modèle k- k

T

kPkkVt

kkT

**.Re

1.

2.Re

1. kPV

t T

95 403 1009* 21 21*


• Le modèle de transport du tenseur visqueux (SST)

12;1max aF

kT

2

22

500;

09.02maxtanh

yy

kF

kPkkVt

kkT

**.Re

1.

kFkPVt T

21

21 12.

Re

1.

4

22

21

4;

500;

09.0maxmintanh

yCD

k

yy

kF

k

202 10;2

max

kCDk

31.01 a 09.0* 41.0


Results

2 meshes results

Fine mesh, 27501 pointsCoarse mesh, 6975 points

Lift coefficient

Fixed incidence case

Turbulence Reynolds Number

k- model with imposed transition at s/c=0.2

Différents model with or without transition


Fully turbulent Transition fixed at s/c=0.2 Transition increasing linéairly between s/c=0.1

and s/c=0.3

Velocity Profiles

Velocity Profiles

SST model for differents values of k

SST models for differents transition localisations and

k=0.001


15 deg: SST model with transition fixed at s/c=0.05

15 deg: SST model fully turbulent


Vortex shedding with a characteristic dimensionless frequency of k= 0.51

12°: k- model fully turbulent

12°: SST model fully turbulent

12°: SSTmodel with transition location at s/c=0.2

Turbulence Reynolds NumberPitching motion, (t)=0+cos(t)0=6deg, 6 deg, k=c/2U=0.188

Lift coefficient Pitching motion, (t)=0+cos(t)0=6deg, 6 deg, k=c/2U=0.188

Hysteresis loops

Velocity Profiles

SST model with transition located at s/c=0.2 an k-model fully turbulent





• Conclusions


• Using such ELDV measurement methods, the boundary-layer behaviour can be fully investigated and characterized in a moving frame of reference.

• Analysis of the effects of forced unsteadiness (due to the pitching motion) on B.L.

• Dependence on turbulence model and transition

• Better agreement with experiment for transitionnal models for static incidence, before stall. Fully turbulent dodels are more adapted for oscillation case

Conclusions

DETAILED EVALUATION OF CFD PREDICTIONS AGAINST LDA MEASUREMENTS FOR FLOW ON AN AEROFOIL A. Benyahia...

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