Free surface volume problem

Yogesh prajapati

hi I have to make analysis on fluent for....There is an open tank which contains water up to some level,remaining part of tank is open to atmosphere having air.At the bottom of the tank there is inlet and outlet which is connected to pump ,means it is flow circulation of water in tank at constant rate.in suction side of the pump there is vortex formation which also suck air with water ,means it is two phase problem.I unable to solve this problem. i am eager for response.