Turbulent two phases fill tank

Hello,

I'm new on this :D

I'm doing the simulation of a break pressure tank, and I want to add the effect of gravity. I am doing it through a turbulent, time-dependent two phases study.

I try to add a volumetric force, but I do not know how to do it right in a turbulent flow.

How can I do it??

Thanks for the help you can give me.