Negative pressures
 

Hi foamers,

I have to simulate the flow in a cylindrical duct (diameter=0.24 mm) . The flow is made by liquid (e.g. water) that is injected in the duct from a cubic capacity at 160 bar and arrives in another cubic capacity at 1.5 bar. The geometry is pretty simple and is shown in the attached image "GEOMETRY". So, I simulate the case with InterPhaseChangeFoam because I want to study the cavitation occurring in the duct. However I obtain high negative pressures , as shown in the figure "p_results". I don't konw how to interpret these values. Are these values relative to a pressure reference value or are they absolute values? In the latter case: how is it possible to obtain negative absolute pressure without a solver crash?

I attach the p_rgh boundary condition in the 0 folder:

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.0.1 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [1 -1 -2 0 0];

internalField uniform 160e5;

boundaryField
{
inlet
{
type fixedValue;
value uniform 160e5;
U U;
rho rho;
psi none;
gamma 1;


}

outlet
{
type fixedValue;
value uniform 1.5e5;
}

wall
{
type zeroGradient;
}

cyl
{
type zeroGradient;
}

frontBack
{
type empty;
}
}

// ************************************************** *********************** //

Thank you in advance for your attention.

Your output in Paraview are always relative pressures with the datum being atmospheric (I suppose unless otherwise specified).

Thank you for tour reply msuaeronautics.
Can you explain me how to set the reference pressure in OpenFoam or Paraview in order to get only positive relative pressures?