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rhoSimpleFoam convergence problem

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Old   May 21, 2011, 04:03
Default rhoSimpleFoam convergence problem
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Hanan Einav-Levy
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Hello,

I am trying to solve the simple case of laminar flow in a tube.
basically what is described here
http://www.somogyibence.hu/documents.../Cornell1.html ,
only i wish to have a heated wall and so the density should change, so I looked at the openFoam solvers, and chose rhoSimpleFoam.

I have given the same equivalent BCs as in the link above, and also played with inletoutlet type BCs, but with out success, i can not get convergence and i see that the pressure is the main problem, it oscilates all the time and never convereges (together with Ux, the velocity in the axial direction).

I am looking for suggestions on relaxation factors, or anything else that is the correct way to get a solution for this simulation (mesh suggestions?, it's simply a blockmesh with simpleGrading (1 1 1 ) )

Thanks,
Hanan.
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Old   May 25, 2011, 11:03
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David Gaden
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Two grasp-at-straws suggestions:

- Play with the gravity. Start with a low value, and increment it, using the latest solution each time. This may smooth out the instabilities.

- Try using a transient algorithm, and look for steady state conditions to develop.
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Old   May 25, 2011, 16:34
Default Thanks, i'll try it
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Hanan Einav-Levy
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can you point out a suitable transient algorithm? i'm still not very familiar with the different solution algorithms.
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Old   May 25, 2011, 16:57
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David Gaden
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Is there a buoyant piso? Or "pimple"? In OpenFOAM, "SIMPLE" is the chosen steady state algorithm, "PISO" is the chosen transient one. "PIMPLE" is OpenFOAM's own (unfortunately named) algorithm that I believe will switch between PISO and SIMPLE depending on the case directory.
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Old   May 25, 2011, 17:07
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Hanan Einav-Levy
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oh, got ya.
will try.
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heated wall, laminar, pipe flow, rhosimplefoam, tube flow

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