Source balance and Boundary condition

Angela

I had used coupled ns and volume fraction equation to calculate the free surface.Now I can see the wave only when I define the froude number is 1.when the fn becomes small even 0.6,it seems the wave is pressed down.

Because i have gravity force as source term.How to balance the gravity.And how to give the condition of pressure.

And sometimes it seems that there is inflow from outlet!I think it must have some connection with boundary consition.How to give the boundary condition?

Another thing is around interface because of the jump of density of air and water,it seems there should use higher order scheme?

Any suggestions and recommendations are welcome!

Thanks in advance!