GLASGOW 2003 INTEGRATING CFD AND EXPERIMENT

Transcription

1 GLASGOW 2003 INTEGRATING CFD AND EXPERIMENT A Detailed CFD and Experimental Investigation of a Benchmark Turbulent Backward Facing Step Flow Stephen Hall & Tracie Barber University of New South Wales Sydney, Australia

2 INTRODUCTION Turbulent Backward Facing Step benchmark flow Compare Particle Image Velocimetry (PIV) and CFD Not just to check CFD Rather to use the best of each What is the best of each? first steps

3 TURBULENT BACKWARD FACING STEP Mean flow structures Characteristic lines and points Wide velocity, turbulence range Good CFD and PIV test Channel flow u=f(y) t Top surface Top boundary layer Ss(x,y) Second vortex u b y Ys (0,0) Primary vortex x Xs Primary Secondary interface Sp(x,y) Shear layer Bottom surface Reverse boundary layer Xr Dividing streamline Core flow u=0 stagnation Xr Outer layer Inner layer Recovery layer

4 EXPERIMENTAL TEST RIG Dimensions and PIV access PIV Nd:YAG Laser Laser light sheet Light Delivery System Scatters y SIDE VIEW (0,0,0) Cross sectional plane x (0,0,0) x Bell inlet Inlet duct Transition z xy planes Dimensions mm Inlet channel Expansion channel TOP VIEW PIV CCD camera and lens

5 EXPERIMENTAL TEST RIG Clear acrylic light access Low reflection base Full side view

6 EXPERIMENTAL TEST RIG High density PIV seeding critical Particle hollow polymer spheres Venturi jet seeder well upstream

7 HIGH RESOLUTION PIV Basic 2D arrangement Mean flow aligned in light sheet Camera perpendicular to light sheet Light Source Light Delivery Light Scattering Particles y Seeding Camera z Lens x Measurement Region Flow Light Sheet

8 HIGH RESOLUTION PIV

9 HIGH RESOLUTION PIV Constant intensity light sheet Adjustable width and thickness

10 PIV VERIFICATION USING CFD Contours From Standard PIV Images of Okamoto and Watanabe (1999) Contours From a PIV Analysis of the Standard PIV Images

11 PURPOSE OF CFD Not only to validate CFD against experiment But to reveal greater detail about phenomena And supplement experimental results Make full use of the reliability of modern CFD

12 CFD APPROACH 2D RANS finite volume (Fluent) RNG k, RSM turbulence closure (literature) Second order interpolation Ambient and boundary conditions use experimental

13 CFD VERIFICATION ASSESSMENT Key functionals Xr, Xs, Ys, Sp, Ss, Lift, Drag Grid convergence literature 200 cells vertical Iterative convergence 3D vs 2D same grid resolution 3% on Xr Turbulence modeling, is code correct? commercial code

14 CFD AND PIV COMPARISON Many quality CFD and Experimental data sets Most missing complete boundary conditions not previously required Perform both CFD and PIV myself exactly equivalent Work in raw variables u, v, Vmag less need to non dimensionalise Contours variation Streamlines direction

15 MEAN VELOCITY MAGNITUDE Velocity Mag. in CS Plane, (top) PIV, (mid.) RNG k, (bot.) RSM

16 STREAMLINES Streamlines in CS Plane, (top) PIV, (mid.) RNG k, (bot.) RSM

17 U HORIZONTAL VELOCITY Mean Horizontal Velocity in CS Plane, (top) PIV, (mid.) RNG k, (bot.) RSM

18 V VERTICAL VELOCITY Mean Vertical Velocity in CS Plane, (top) PIV, (mid.) RNG k, (bot.) RSM

19 VORTICITY Vorticity Mag. in CS Plane, (top) PIV, (mid.) RNG k, (bot.) RSM

20 VELOCITY MAGNITUDE AND STREAMLINES BEHIND STEP Characteristic Lines in CS Plane, (top) PIV, (mid.) RNG k, (bot.) RSM

21 FOCUSED BEHIND STEP Mean Velocities in CS Plane, (left) PIV, (right) RSM t p =70 µs

22 FOCUSED BEHIND STEP Streamlines in CS Plane, (left) PIV, (right) RSM, t p =70 µs

23 CONCLUSIONS CFD and PIV reveal detailed flow structure Exactly Equivalent simultaneous CFD and PIV Highlights limitations in each Improves confidence in results Essential complimentary techniques

24 FUTURE DIRECTIONS CFD should be first part of any PIV? Unsteady 3D CFD PIV (TR PIV, stereoscopic) Total integration of CFD PIV PIV modifies turbulence closure model throughout CFD error checks PIV and fills in error regions mathematically rigorous

25 PLANES OF INTEREST Inlet Line Inlet Profile Cross Sectional Plane y= Inlet Plane x= 100 Step z y (0,0,0) x Bottom Surface Outlet Plane x= 400 z= z= 0

26 HIGH RESOLUTION PIV Basic sub systems Optimise performance of each Light Source Light Encoding Light Delivery Flow Seeding t Post Processing Filtering Distortion Correction Mapping Image Statistical Analysis Processing Image Trimming Cross correlation Error Checking Storage Control Analysis Light Scattering Particles Light Conditioning Recording

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