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Aerofoil Modelling - Laminar approximation, transition and turbulence modelling.

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Old   January 18, 2014, 06:49
Default Aerofoil Modelling - Laminar approximation, transition and turbulence modelling.
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Craig
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Hello all,

I was wondering if I could get some advice.

I am modelling an aerofoil at various angles of attack and velocities.

I ran some validation cases in 2D and 3D first using a Steady, Laminar model and then using the Implicit Unsteady Spalart-Almaras turbulence model.

Both systems showed reasonable agreement of both lift and drag coefficient for angles of attack up to the plateau at stall condition.

I have a few questions though (the aerofoil under consideration has roughly similar geometry to NACA 4412 or Clark Y):

>> When is it appropriate to use a laminar approximation - could I perhaps assume that the separation of flow and development of a turbulent boundary is negligible for low (0-5 degrees) angles of attack?

>> Am I right in saying that by using an Implicit Unsteady system with Spalart-Almaras turbulence, I am saying that the flow IS turbulent, and that the turbulence model in itself has no way of predicting the transition from laminar to turbulence.

>> Would it be better, perhaps, to use a K-Omega model with the Gamma-Re-Theta transition model such that the CFD may predict transition to a turbulent boundary layer and the position of flow separation ... I tried this, the results seem okay but I don't get a 'trail' of low velocity flow behind the aerofoil as I do in the laminar or Spalart-Almaras case.

Thank you very much!

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Old   January 20, 2014, 06:25
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siamak rahimi ardkapan
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Have you tried to use some transition models? Check out the tutorial.
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