Hydrosatic Head convergence
 

Hi everybody,
i have some issues with a cfd analysis in Fluent.
I want to simulate the "barrier" effect of a bubble curtain on a seacurrent (in the future i will update the current with a sediment concetration).
first of all i found some papers that helped me to set a methodology and a sort of validation for bubble diameter.
Once the bubble formation is validated (without any current) my objective is to insert the bubble formation in a model with a seacurrent. The first step in this case is to set a rectangular domain (all the simulations are 2D) with an inlet velocity, left, of 0.1 m/s and a pressure outlet, at right, at the top there is a free slip wall and at the bottom a no slip wall. Very trivial simulations but when i set the operating density to zero to have the hydrostatic head the solution is very strange: the hydrostatic head is never respected. I forgot to say that the air is compressible instead when the air is incompressible the solution is ok (in the latter the outlet is outflow to keep the hydrostatic head becaus with pressure outlet did not function).
Could anyone help me, please?