Help: apply B.C. in my granular flow model ?
I am modeling a gas-granular flow using FLUENT 6.0. My problem is: A hopper with open bottom and top is filled with sand. It is a transient problem, and the initial condition is that the hopper is almost full of still sand. I model the flow behavior of sand until all sands flow out of hopper. So, my problem is similar to the flow behavior in a hourglass. I am using Eulerian multiphase model. Now, I have question with applying boundary conditions.
(1) The top of hopper is open. No sand will reach here, but gas may flow in or out through this face. I plan to use Pressure-Outlet boundary conditions. I will define the operating pressure to be environment atosmophere pressure, and prescribe zero value for gauge pressure. Because I am not sure the gas is flowing in or out, I am not sure whether my usage of pressure-outlet B.C. is correct. Also, because sands can not reach the top, can I set the granular temperature of sand to zero at the top face?
(2) The bottom of the hopper is also open. The sands are flowing out here but I am also not sure the gas is flowing in or out. I plan to apply outflow boundary condition here for both phases (mix), which means that the normal gradients for all flow variables except pressure are zero. Is this method correct?
I am a new user of FLUENT, and I am eager to get any suggestion or instruction from you. Thank you very much for your generous help.
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