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pressure spikes due to addition/deletion of layers

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Old   October 25, 2011, 08:45
Default pressure spikes due to addition/deletion of layers
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kshitij neroorkar
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Hello All
I was running icoDyMFoam on the tutorial case movingConeTopo. I added one line to icoDyMFoam to write out the maximum pressure in the domain at every time step. I found that almost every time there is a cell addition/deletion, there is a pressure spike in the domain. Has anyone else seen these spikes? and has anyone found a solution?
Thanks
Kshitij
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Old   October 26, 2011, 03:48
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Karl-Johan Nogenmyr
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Hi,

Which version are you using? The implementation of the movingCone(or Body)TopoMesh is altered in later revisions of the 1.6-ext version. In the newer (and parallel) version, a lot of lines are commented out in Foam::movingBodyTopoFvMesh::update() . These lines affects how meshPhi (in fvc::makeAbsolute(phi, U) and fvc::makeRelative(phi, U)) is determined (if I understood correctly). If meshPhi is wrong, I would guess it could result in pressure peaks. Do you have any possibility to repeat your check on a previous, non-parallel version of the movingCone/Body case?

Kalle
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Old   October 27, 2011, 09:48
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kshitij neroorkar
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Hi Kalle
Thanks for your post. We updated to the latest version of 1.6-ext to see what difference it made, and we found that the spikes were considerably smaller, but still existed.
if you/ anyone else would like to test this, you can just add the following functionObject to the controlDict and run the movingConeTopo test case with icoDyMFoam.
Thanks a lot for your help
Kshitij


functions{
fieldMinMax
{
type fieldMinMax;
functionObjectLibs ("libfieldFunctionObjects.so");
log yes;
outputControl timeStep;
outputInterval 1;
mode magnitude;
fields
(
U
p
);
}
}
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Old   October 28, 2011, 03:35
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Karl-Johan Nogenmyr
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Hi,

Thank you for bringing this up. I tried the case, and there are spikes as you say. Pressure is initially fluctuating around ~4e-4 to ~1e-4 as layerAR is working. I tried a few modifications to the movingBodyTopoFvMesh-class without success. Right now I do not have any clue how to get on. To solve this issue, I think one should find out how this adding layer functionality is handled within the finite volume method. This paper may provide some help:

http://web.univ-ubs.fr/limatb/EG2M/D...pers/01178.pdf see especially section 2.3

I also need to fix this for my own work, so I will likely get back to it when I have time.

Regards,
Kalle
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Old   October 28, 2011, 08:58
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kshitij neroorkar
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Hi Kalle
Thanks for looking into this and thanks for the paper. Please let me know if you find anything.
Kshitij
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