Dear all:

I wonder in what conditions that one can completly ignore the bondary layer in the wall by imposing free slip boundary condition.

I am simulating a supersonic jet flow that flows near a wall, but all that I want to know is that the force generated by the jet impinging on an object mounted on that wall.

How reliable is the simulation if I do not resolve the boundary layer near the wall (Just using high reynolds number k-e) knowing that my boundary layer must be very very small for supersonic flow (Mach=2.3).

Thank's for any response and help

Danny

It depends on several things. If the flow is completely attached, then you should get a decent estimate of the pressure forces, but viscous drag will not be computed correctly, since it obviously depends on the velocity gradient at the wall. If the flow separates then the immediate question is how valid your separation prediction is, since turbulent and laminar flows can separate in completely different ways. In that case even your pressure drag may be way off. Since you are dealing with a strong supersonic flow, the issue of shocks and shock/boundary layer interaction should be considered, particularly if there is shock-induced separation. Another complication arises if the surface is not adiabatic, and you must consider heat transfer - another phenomenon that requires a good simulation of gradients at and near the surface.