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Negative absolute pressure in rhoPorousMRFSimpleFoam

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Old   January 14, 2013, 10:22
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Thank you, Niklas and maHein.

I monitored the outlet pressure using this code:
pOutlet
{
type patchAverage;
functionObjectLibs ("libsimpleFunctionObjects.so");
verbose true;
patches (outlet);
log true;
fields
(
p
);
}
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Old   March 5, 2013, 13:10
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then its incorrect to set totalPressure at outlet?
I have 2 totalPressure BC at inlet and outlet.at inlet it behaves somewhat good(except supersonic velocity at 3-4 begining time steps that should be subsonic in real but it modifies at later time steps and becomes subsonic) but when outlet opens pressure goes too little and velocity increases a lot and problem diverges.
could anyone argue about the formula I have written at other thread also?
Code:
p0_2/pow(1+(gamma-1)/2*magSqr(internalField(U))/(gamma*R*internalField(T)),3.5)
thanks.
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Old   March 5, 2013, 13:18
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dear Omkar I have a foolish question!
how do you plot residuals and othe variables like you did above?
I want to plot residuals by iteration numbers like you did but pyFoam draws residuals( and not variables at all) by time step in x-axis.
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Old   March 8, 2013, 04:56
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can anyone guide me through two questions i propounded at two posts above?
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Old   March 8, 2013, 09:56
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You can plot residuals using gnuplot as mentioned in this post:

http://www.cfd-online.com/Forums/ope...tml#post410537

I am not sure about using total pressure at both ends. When you specify total pressure at both ends, it is like fixing the loss across the system rather than letting the system decide. This is what I think, I am not sure about it though.

Plus, as per the discussions above, if the flow is leaving the domain, OF will considered the input value as static pressure because the term 1.0 - pos(phip) will go to zero.
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Old   March 12, 2013, 05:13
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I was looking at the files posted by you and those modified by Niklas to understand the reason of the improvement. When you say "The damping for pressure is amazing" are you referring to the decrease in tolerance from 1e-6; to in 1e-9; the fvSolution?
...
p
{
solver GAMG;
tolerance 1e-9;
relTol 0.1;
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Old   March 12, 2013, 09:04
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No. What I meant was that the pressure values stabilized quickly.
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Old   March 14, 2013, 18:49
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how can avoid high velocities at first iterations?maybe limiting of velocity to mach velocity?i tried but without useful result.
Efforts are thanked
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Old   March 15, 2013, 06:42
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has anyone done a progress on the issue of high velocities at first few iterations in total pressure model of BC?
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