# Negative pressures

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January 28, 2013, 07:15
Negative pressures
#1
New Member

Elio Bufi
Join Date: Jan 2013
Posts: 5
Rep Power: 4
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
{
}

cyl
{
}

frontBack
{
type empty;
}
}

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

Attached Images
 GEOMETRY.jpg (100.4 KB, 13 views) p_results.jpg (97.3 KB, 16 views)

 January 28, 2013, 12:04 #2 Member   Eric R Join Date: Jul 2012 Location: Mississippi State University Posts: 73 Rep Power: 4 Your output in Paraview are always relative pressures with the datum being atmospheric (I suppose unless otherwise specified).

 January 29, 2013, 04:08 #3 New Member   Elio Bufi Join Date: Jan 2013 Posts: 5 Rep Power: 4 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?

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