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low reynolds airfoil simulation

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Old   March 1, 2010, 15:30
Default low reynolds airfoil simulation
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Hello everybody

Im trying to simulate low reynolds airfoil flow. The Re number is about 4*10^5, and the goal is to get the airfoil polar, drag against lift curve. I try to do that using k-epsilon viscous model, and y+=1,by means of a boundary layer, but the polar differs to much from the experimental one.

Could you please tell me wich viscous model would be the appropiate for that kind of simulations. I heard that some people uses michel criterion or e^n models, to calculate the transition point between laminar and turbulent, using user-defined functions. Others say that spalart-allmaras is the best one for low reynolds.

Best Regards
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Old   March 1, 2010, 18:09
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hi! i use the spalart-almaras, it gives an accurate Cl for the angles of attack before stall but i can not have good results in stall angle. Also the Cd diverges a lot from the experimental values.
Is there anything common between mine and yours results?
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Old   March 3, 2010, 08:59
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try the SST transitional model (4 equations model) findable in fluent 12.0.
Be careful on the Turbulent Intensity and Turbulent Viscosity Ratio values that you will put in the boundary conditions. You should find better agreement using low turbulent values with high AoA and high turbulent values with low AoA.
However stalled AoA is very difficult to simulate with RANS steady models, you have to try Unsteady RANS models or better DES model with SST-Kw to obtain better results.
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Old   March 3, 2010, 13:51
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I dont mind about stall values, im only worried about having more accurate cd vs cl values outside the stall threshold.

But, is this k-omega SST turbulent model different from the 2 equations SST at fluent 6.2? Perhaps it incorporate added equations to evaluate transition between laminar and turbulent.

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