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

Hasselhoff June 2, 2009 07:43

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/mē), 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
{
type zeroGradient;

}
inlet
{
type zeroGradient;

}
}



The 0/U looks like:


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

internalField uniform (0 0 0);

boundaryField
{
outlet
{
type zeroGradient;

}
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 08:12

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.

I hope this is helpful,
Dragos

Hasselhoff June 29, 2009 18:43

Thanks for the answer. You're right, I didn't consider that..

:)


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