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April 16, 2011, 12:15 
rhoPimpleFoam algorithm

#1  
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Perry L. Johnson
Join Date: Feb 2011
Location: Orlando, FL, USA
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I am working in OF v1.7.1 and have a couple quick questions regarding the implementation of the compressible PISOSIMPLE algorithm:
1) On line 00095 of the rhoPimpleFoam/pEqn.H code: Why is the if statement commented out? Should the relaxation of pressure really be allowed in the final outer iteration? Quote:
Quote:


April 18, 2011, 02:57 

#2 
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Christian Lucas
Join Date: Aug 2009
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Hi,
you are correct, there should be no relaxation in the last iteration because otherwise you get a continuity error (which is very large if you look at the tutorial case). I'm not sure about the energy equation but would be interested in your result. Regards, Christian 

April 18, 2011, 19:22 

#3  
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Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
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Quote:
Quote:
However this aspect might influence convergence rate, but it should not affect the results. Best,
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

April 20, 2011, 09:40 

#4 
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Perry L. Johnson
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Alberto and Christian,
Thank you for entertaining my curiosities. I will let you know anything I find through experimentation, though it seems as if Alberto does not expect much difference on either point. For the interested foamer stumbling across this thread, I suggest reviewing the following thread for a more involved discussion of relaxation Suggested unsteady, implicit solver stable with arbitrarily large time steps Regards, Perry 

April 20, 2011, 21:56 

#5  
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Alberto Passalacqua
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Yes, I do not expect any difference on the solution.
Quote:
Best,
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

July 27, 2015, 10:16 

#6  
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Christa
Join Date: Apr 2011
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Quote:
this commentedout IF statement has been removed from OF v.2.4, as can be seen here: https://github.com/OpenFOAM/OpenFOAM...oam/pEqn.H#L92 I am getting massive timestep continuity errors and no pressure convergence for what should be a very straightforward problem of orthogonal mesh and subsonic gas flow. After searching a lot in this forum (and it is quite hard to get the keywords right!) I think that if I don't relax the pressure in the last outer iteration my solution may converge. Has anyone tried to do this in newer versions of OF? Anyone know why the commented out section was removed? Can you please guide me to where OF explains changes from one version to the next? Thanks, Christa 

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