rhoSimpleFoam convergence problem

hananfoam · May 21, 2011, 04:03

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.

marupio · May 25, 2011, 11:03

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.

hananfoam · May 25, 2011, 16:34

can you point out a suitable transient algorithm? i'm still not very familiar with the different solution algorithms.

marupio · May 25, 2011, 16:57

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.

hananfoam · May 25, 2011, 17:07

oh, got ya.
will try.

May 21, 2011, 04:03	rhoSimpleFoam convergence problem	#1
hananfoam New Member Hanan Einav-Levy Join Date: May 2011 Posts: 10 Rep Power: 14	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.

May 25, 2011, 16:34	Thanks, i'll try it	#3
hananfoam New Member Hanan Einav-Levy Join Date: May 2011 Posts: 10 Rep Power: 14	can you point out a suitable transient algorithm? i'm still not very familiar with the different solution algorithms.

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May 25, 2011, 11:03		#2
marupio Senior Member David Gaden Join Date: Apr 2009 Location: Winnipeg, Canada Posts: 437 Rep Power: 21	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.

May 25, 2011, 16:57		#4
marupio Senior Member David Gaden Join Date: Apr 2009 Location: Winnipeg, Canada Posts: 437 Rep Power: 21	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.

May 25, 2011, 17:07		#5
hananfoam New Member Hanan Einav-Levy Join Date: May 2011 Posts: 10 Rep Power: 14	oh, got ya. will try.