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-   -   pressure ratio simpleFoam boundary case/0/p (https://www.cfd-online.com/Forums/openfoam/65045-pressure-ratio-simplefoam-boundary-case-0-p.html)

 Hasselhoff June 2, 2009 08:43

pressure ratio simpleFoam boundary case/0/p

Hi Folks!

I'm trying to calculate the inlet pressure of a test element, which represents a stepped seal labyrinth of a turboengine.This actually looks quite similar to a pipe (one Volume, inlet, outlet, wall).
I want to compare these pressure results with experimental data files.
The solver I use is simpleFoam, the velocity at the inlet is 10.4546m/s, the outlet pressure is constant (1bar)

my problem seems to be very simple, but I'm struggling real hard with the boundary conditions in 0/p..
Due to the dimensions (N/m²), I also set the internalField + outlet value 1e5, but in that case, no velocity profile was visualized and the pressure values were not realistic. It should be a pressure ratio (inlet- outlet) of 1.07
Paraview shows negative pressure values, if I use the following configuration:

dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
outlet
{
type fixedValue;
value uniform 0;

}
wand
{

}
inlet
{

}
}

The 0/U looks like:

dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
outlet
{

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

}
inlet
{
type fixedValue;
value uniform (10.4546 0 0);
}
}

Can u help me with this? If you know any case where I can see how it's done please let me know. I couldn't find anything..:confused:

thank u,

Mitch

 dmoroian June 2, 2009 09:12

Hello Mitch,
Due to the fact that you're using an incompressible flow solver, the pressure dimension is not N/m2 but m2/s2 (the pressure is divided by the density). Moreover, the computed value of the pressure is a relative one (p_calculated = p-p_reference) so there is no unphysical behavior if you get negative pressures, it just means that the absolute pressure happens to be smaller than the reference pressure you wrote in the dictionary.