Outlet for transient cases in two phase flow

I have problems converging a two phase flow with water and air.

When the water exits the computational domain, I can see reflection of water. Also some cases diverge before the water reaches the outlet boundary.

I send in attachment screenschoots of several time steps. Where you can see the reflections in the boundary conditions.

Is there a way to say to a outlet condition that I only want air to enter the domain? Star-ccm+ has this option in the two-phase flow option.

Thanks in advance