|January 18, 2014, 06:49||
Aerofoil Modelling - Laminar approximation, transition and turbulence modelling.
Join Date: Oct 2013
Posts: 11Rep Power: 4
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!
|January 20, 2014, 06:25||
siamak rahimi ardkapan
Join Date: Jul 2010
Location: Copenhagen, Denmark
Posts: 218Rep Power: 10
Have you tried to use some transition models? Check out the tutorial.
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