Unsteady simulation on the flow around Naca0012

Peter Pan Zhang

I am going to simulate the unsteady vortex shedding from a stalled airfoil NACA0012 by FLUENT6.2. The chord length is 1m and the incoming flow veloctiy is about 10m/s, these yeild the Reynolds number at the order of 10e5. At attack angle 20, the flow around the airfoil should be unsteady from previous studies, and there are unsteady vortex shedding.

I can get the unsteady result using laminar equation, but when I change the equation to SST k-w or k-w model, the unsteady vortex shedding is gone and just a steady separation zone on the upside of the airfoil exist. The min distance of the mesh to the wall is set to make sure y+<1 and the mesh in the wake of the airfoil also be refined. I use the same grid and parameter settings to simulate the flow around circular cylinder, and can predict the unsteady force corretly.

So I don't know what's wrong with my case, anyboby who has done similar simulation can give me some advises. Thanks!