granular flow

Lydia

Hi, Ive got the following problem: I want to simulate the discharge of a hopper. I use the eulerian model with 2 phases (air and sand). I use also a 2d geometry designed and meshed with gambit. For BC I choose velocity inlet and pressure outlet. The flow should be gravity driven. The problem is, that the continuity does not converge!! Even if I try to get a solution with the unsteady simulation and realy small time steps. So what could be the problem here? And how can I make sure that just a wanted mass flow rate is taken out over the outlet? Because the real problem is solved with a screwconveyor. You see I'm new and not realy familiar with fluent yet. So please help me!!!

thanks