[tankerp]

I urgently need clarification on pressure boundary conditions for my simulation.

1. I am performing a multiphase simulation in a water column using twoPhaseEulerFoam. The entire column is filled with water. The second phase enters through an inlet at the bottom of the column (prescribing velocity). Gravity is in the direction against the flow.

I am currently using the following BC:

For p:

internalField       uniform 0;
     inlet
     {
         type               calculated;
         value              $internalField;//
         }    

       outlet
         {
          type               calculated;
          value              $internalField;
         }

For p_rgh:

internalField       uniform 0;

        inlet
     {
          type            fixedFluxPressure;
          value           $internalField;
         }    

      outlet
         {
          type            prghPressure;
          p               $internalField;
          value           $internalField;
         }

For U:

inlet
        {
        type               fixedValue;
        value              uniform (0 1 0);
        }

    outlet
    {
        type               pressureInletOutletVelocity;
         phi                phi.air;
        value              $internalField;
    }

2. For some tutorials, the initial value in the internalfield are 0 for p and p_rgh and for some others they are 1e5. How is this decided?

[olesen]

Compressible vs. incompressible?

[tankerp]

The twophaseeulerfoam solver is a compressible solver

[Tobi]

Hi,



a) please use code tags
b) Mark knows that and just gave you the hint


for incompressible flows, the pressure gradient is of interest (not the absolute value)
for compressible cases, the pressure gradient, as well as the absolute value, is of importance (thermodynamic - calculation of rho)