[JakPink]

Hi Everybody I am new to CFD online and this is my first post.

I have been working on a project in OpenFOAM regarding a Helium jet blowing into water (to simulate a medical plasma jet), using the multiphaseInterFoam solver with three fluids (helium, air and water).

My query is that I would like the top boundary of my mesh to allow air to move freely both ways across it, and also allow Helium to float away out of the boundary but not inwards.

Please could anybody suggest how best to define boundary conditions for this? Concerning the air phase they are currently:

alpha.air
atmosphere
{
type inletOutlet;
inletValue uniform 1;
value uniform 1;
}

p_rgh
atmosphere
{
type totalPressure;
p0 uniform 100000;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 100000;
}

U
atmosphere
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}

Thank you in advance for any help!