[Babak]

Hi

I am trying to model the air-water flow in a tank using mixture model, the volume fraction of air is 5-10%, I easily get convergence for the single phase case, for two phase mixture model the solution is very unstable. I have played wit relaxation factors and used the single phase solution as the primary guess. Can some one with similar experience give me some advice on how to resolve this?

Can this be because of the boundary condition at the free surface? What is the suitable boundary condition at the surface? I am using a wall with no shear stress for the surface boundary right now.