Emptying of a tank using VOF modelling
 

I am trying to model a tank with an open top and a spherical base filled with water. There is a small outlet at the center of the base and the tank is emptying under the action of gravity. I am using an axisymmetric domain, standard K-epsilon turbulence model, VOF modelling and geo-reconstruct scheme. I am having difficulty in getting a solution when I apply a pressure difference between inlet and outlet. Also when I check the mass flow rates at different cross-sections in my tank and the outlet they are different, which I think should be the same. What should I do to handle this particular problem properly?

I think you have not setted boundary and operating conditions.

Thanks.. You are right. With appropriate operating and boundary conditions the solution runs nicely

Now I am simulating with components of gravity in both x and y dimensions. For this I have to shift to 2D planer domain from axisymmetric. What might be the relation of mass flow rate I get in the 2D case in comparison to the axisymmetric case?