issue of a liquid
 

Somebody can advise, how cases with the issue of a liquid from a tank are considered? For example, we have a glass of water with small hole in bottom. By gravity forces water starts to be poured out of a glass. It is required to determine position of a water level for the various moments of time.

Of course it is Buoyancy-driven Flows. Maybe to enter two scalars. For example H2O(SC1) and AIR(SC2) and to watch fields of concentration of these scalars?

Perhaps this is Free-Surface problem?

I shall be grateful for any advices.