[KTG]

Hello Foamers,

I am having a strange issue when using interFoam with a hydrostatic boundary condition. The general setting is that I have two plates with a narrow gap between them. A thick, laminar liquid is flowing into the gap under a constant head, hydrostatic boundary condition. So I am using the interFoam solver. The liquid that is displacing the air is orders of magnitude denser, so I just set the boundaries to zero pressure where the air is exiting the gap.

flow.png shows the simulation after 40 seconds.

backflow.png is the same, but with forward streamlines. You can clearly see that the section that is assigned the uniformDensityHydrostaticPressure condition has split itself between inflow and outflow. I can't figure this out, because the pressure there is greater than zero.

Here are the boundary conditions for pgh (the "freeinlet" patch is located directly above the uniformDensityHydrostaticPressure patch):

boundaryField
{
    inlet
  
     {
        type            uniformDensityHydrostaticPressure;
        rho             1263.9;
        pRefValue       0;
        pRefPoint       (0 0 .16);
        value           uniform 0; // optional initial value
    }

    freeinlet
    {
        type            fixedValue;
        value            uniform 0;

    }
    

    outlet
    {
        type            fixedValue;
        value            uniform 0;

    }

    wedgewalls
    {
        type            fixedFluxPressure;    
    }    

    lid
    {
        type            fixedValue;
        value            uniform 0;

    }

}

for U:

boundaryField
{

    inlet
    {
        type        zeroGradient;
    }    

    freeinlet
    {
        type        zeroGradient;
    }    

    outlet
    {
          type            inletOutlet;
          inletValue      uniform (0 0 0);
          value              uniform (0 0 0);
    }

    wedgewalls
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    lid
    {
        type            slip;
    }


}

and alpha.water:

 boundaryField
{
    inlet
    {
        type            inletOutlet;
        inletValue      uniform 1;
        value           uniform 0;
    }
    freeinlet
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value           uniform 0;
    }
    outlet
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value           uniform 0;
    }
    wedgewalls
    {
        type            zeroGradient;
    }
    lid
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value           uniform 0;
    }
    defaultFaces
    {
        type            empty;
    }
}

Any ideas would be greatly appreciated! I have been messing with the geometry of this to try to make it a little more stable, but I think the real issue is in my boundary conditions. I can't figure out why the zero pressure boundaries seem to have zero flux, but the hydrostatic one has some flow that seems to defy the pressure gradient.

Thanks!