[JAndreotti]

I'm trying to simulate the dynamic stall of a wing and due to the boundary layer refinements I'm getting very high courant numbers near the walls. The courant numbers for the rest of the flow seem to be ok (< 1). So, is it acceptable under these circumstances to have high courant numbers? And, for this application, what is a good criterion to set the time-step (I'm only interested in the large periodic oscillations in lift and drag)?

[FMDenaro]

Originally Posted by JAndreotti

I'm trying to simulate the dynamic stall of a wing and due to the boundary layer refinements I'm getting very high courant numbers near the walls. The courant numbers for the rest of the flow seem to be ok (< 1). So, is it acceptable under these circumstances to have high courant numbers? And, for this application, what is a good criterion to set the time-step (I'm only interested in the large periodic oscillations in lift and drag)?

That sounds very strange, close to a wall the turbulent boundary layer is mainly governed by the viscous sub-layer. The cfl should be small.