[lincoln53]

Hello everyone,

I am doing hydraulic tank analysis for my master thesis. The hydraulic tank has a suction and return line. In addition, there is a hole open to the atmosphere at the top of the tank. In fact, after the oil circulates through the entire system, the tank is not completely filled with oil because it contains very little air, and a certain part is left empty. The purpose of the hole opening to the atmosphere can be said to be that this rising air leaves the system. I have the inlet (return line) mass flow rate available. Assuming that there is a certain amount of air in the oil (2%), I define it as velocity inlet to the return part (by converting the mass flow rate to velocity) and send it to the system with 2% air. There is actually a pump in the outlet line, but I ignore the pump part because it doesn't concern me. My aim is to keep the inlet and outlet mass flow rates equal, to observe how much air goes into the suction line and to change the design and minimize the air going to this outlet.

I am using VoF to model the system. The primary phase is oil, the second phase is air. When I define the outlet as a pressure outlet and give it 150 bar (Gauge), the mass flow increases incredibly, so it doesn't make sense. When I take the gauge as 0, oil cannot come out of the suction line at all, on the contrary, there is a rotation in the suction line and mass is not preserved. When I give Suction Pressure (0.2 bar), the mass flow rate increases again and the mass is not preserved.

When I give a Mass Flow outlet, I interfere with the system a lot and it also asks me to define an air flow to the outlet, when I define it as 0, it does not pass air at all and the results are wrong.

When I make the suction line a velocity inlet and define a negative velocity, I get logical results, but when I change the air design I give (such as putting a baffle in between), there is no change, I get the result when I did not change the design (I think it should change)

What kind of boundary condition should I define as an output?

My geometry is 3D and I am making a steady state solution.

Kind regards.