Free surface flow,Initial & B.C.s?(URGENT)

tuks

hi friends, I am solving a problem of flow in a RECTANGULAR TANK. Dimensions of tank are 1mX1.5mX1m. The inlet is at point [0 0.5 0.5] and outlet is at [1 0.9 0.5] and vent is at [0.5 1.5 0.5] all having radius=0.75m. I want to solve it for two phase (Water + Air) system where upto 1m tank is filled with liquid water and rest with Air. At inlet only Water is coming and at outlet as well only Water is going out. The air is generated at Air-Water interface (analogous to CO2 generation) and will go out through vent.

Aim: to get velocity profile for water flow.

PROBLEMS: (1)How to define the outlet boundary condition so that water level will be maintained constant? (2)How to specify the interface source term. (3) Can we solve this problem by defining two different domains for Water and Air sections respectively and then domain interface at actual Air-Water interface.

Please help me out earliest. Thank You TUKS