# porousSimpleFoam: oscillating velocity in the porous zone

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 December 3, 2010, 15:49 porousSimpleFoam: oscillating velocity in the porous zone #1 New Member   Sergei D. Join Date: Mar 2009 Posts: 4 Rep Power: 0 Hello! I try to use a porousSimpleFoam solver to simulate a flow in a 2D channel from two equal parts, a free flow part and a porous part (wall's type set in the 'slip' for simplicity): Base case is a angleDictImplicit. My results are a good p, but strange oscillating U. On the next sctrutured mesh: I get this solution: Velocity field is: One can see what velocity is good but slightly oscillated on porous boundary. So, question is: Are such oscillations caused by a stepwise porous source? If yes, how can I specify smooth porous source? But more bad situation have place on non-structured mesh. Mesh is Solution is: One can see very oscillating velocity in the porous region. So, why this happens? Non-orthogonal correction not helped. Thanks.

 January 3, 2011, 13:28 #2 New Member   Marc-Florian Uth Join Date: Jan 2010 Posts: 10 Rep Power: 16 Hi! I have exactly the same problem. Did you find a solution for that? kind regards, marc

 February 10, 2011, 07:44 #3 Assistant Moderator   Bernhard Gschaider Join Date: Mar 2009 Posts: 4,225 Rep Power: 51 This problem has been reported to http://www.openfoam.com/mantisbt/view.php?id=134. A fix is also described there cheng1988sjtu and Bahram like this.

 January 27, 2014, 08:27 #4 New Member   Faraj Join Date: Feb 2010 Posts: 22 Rep Power: 16 This is not a problem. Just change under-relaxation factor to 0.0001, and you will not have this oscillations. OpenFOAM software is the best software among all CFD, and being unexperienced in CFD, does not meam that OpenFOAM has bugs, that should be reported like that...

January 28, 2014, 05:11
#5
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Bernhard Gschaider
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Quote:
 Originally Posted by Filankes This is not a problem. Just change under-relaxation factor to 0.0001, and you will not have this oscillations.
This is absolute brilliant: under-relaxation is like alcohol: if you take enough you see no problems anymore. Getting things done will take forever, but who cares?
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January 29, 2014, 18:02
#6
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Faraj
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Quote:
 Originally Posted by gschaider This is absolute brilliant: under-relaxation is like alcohol: if you take enough you see no problems anymore. Getting things done will take forever, but who cares?
Hi Bernhard,

You are right it takes a lot of time of calculations.

In industrial application it is not good idea to use it.

However, if you use 10 000 - 17 000 cells (hex) for the case proposed in this topic, and make underrelaxation = 0.0001, it will take 30 minutes to have an Exelent solution.

Unfortunately, tetrahedral cells were used, and seems to me under-relaxation 0.0001 will take a day or two for this simulation.

I feel like it is not industrial application, since it is tetrahedral, and 1-2 days is possible to give to get better velocity profile)) corrected pressure loss))

se9a
btw, I forgot to mension - I always use 7 cells in flow direction of porous zone + 0.0001 underrelaxation.

other regions can have very coarse mesh, since they are of no interest I guess

 August 8, 2014, 03:26 #7 New Member     Bahram Haddadi Join Date: Feb 2014 Location: Vienna, Austria Posts: 20 Rep Power: 12 Thanks Bernhard It worked like magic

September 23, 2014, 04:18
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Quote:
 Originally Posted by gschaider This problem has been reported to http://www.openfoam.com/mantisbt/view.php?id=134. A fix is also described there
Dear Bernhard

Thanks for the help. I tried it, somehow it works, but as it is also mentioned in there it causes a huge conservation error. Do you have any idea where does this error comes from? any help appreciated!

Best regards
Bahram

September 23, 2014, 14:01
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Bernhard Gschaider
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Quote:
 Originally Posted by Bahram Dear Bernhard Thanks for the help. I tried it, somehow it works, but as it is also mentioned in there it causes a huge conservation error. Do you have any idea where does this error comes from? any help appreciated! Best regards Bahram
Have a look at the link http://www.openfoam.com/mantisbt/view.php?id=134

It is not my claim and I never checked how big HUGE is
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 September 24, 2014, 03:10 #10 New Member     Bahram Haddadi Join Date: Feb 2014 Location: Vienna, Austria Posts: 20 Rep Power: 12 Thanks a lot for quick respond, I have already checked that page but as I said before that idea causes some errors and there is not any clue in there to solve this fluctuating velocity without loosing or gaining some mass!!!

 January 9, 2016, 10:38 #11 Member   Yan Wang Join Date: May 2015 Location: Beijing Posts: 41 Rep Power: 10 Hi guys, I also have an oscillating velocity when simulating flow through different porous media adjacent to each other using fvOptions as well as the implicit treatment in porousSimpleFoam. So the solution for this problem is to use a small under-relaxation factor like 0.0001? I try this, and it does work, nearly perfectly. But any other new idea? Anyone know if fluent has the same problem? Regards, Yan __________________ Blog: http://blog.sina.com.cn/multiphyzks RG:https://www.researchgate.net/profile/Yan_Wang154

January 10, 2016, 06:37
Fluen?
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Ray
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Quote:
 Originally Posted by gschaider Have a look at the link http://www.openfoam.com/mantisbt/view.php?id=134 It is not my claim and I never checked how big HUGE is
Dear Assistant Moderator

Do you have experience in fluent too? I have some questions about creating profile, etc.

Your quick help is highly appreciated?

Kindest Regards, Rayman

 July 19, 2016, 04:29 #13 New Member   Steven Beale Join Date: Jan 2011 Posts: 4 Rep Power: 15 The instability is due to a co-located (aka Rhie and Chow) scheme being employed. The variable porosity problem is a classic benchmark for such schemes. There have been a number of solutions/modifications proposed in the literature over the years, with varying degrees of success. Staggered schemes do not suffer from this deficiency.

 October 28, 2016, 08:11 #14 New Member   Roberto Join Date: May 2016 Posts: 17 Rep Power: 9 Hello! Is it possible to "vanish" those oscillations just changing configurations in fvSchemes/fvSolutions? So far I just have found threads related to implementation of new algorithm. I have the same problem and just changing the under-relaxation factors to 0.0001 will not solve my problem. I thought using the solver porousSimpleFoam would help, but it doesn't. Is there somebody who could give me some hints? Best regards, Roberto

 August 9, 2017, 04:26 #15 New Member   karundev Join Date: Jun 2017 Location: India Posts: 25 Rep Power: 8 how this oscillation can be corrected?. under relaxation factor change didn't helped me.

August 9, 2017, 04:38
pororusSimpleFoam
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Quote:
 Originally Posted by gschaider This problem has been reported to http://www.openfoam.com/mantisbt/view.php?id=134. A fix is also described there

Last edited by krndv; August 9, 2017 at 05:51.

 August 9, 2017, 04:58 #17 New Member   Sebastian Join Date: Feb 2017 Posts: 22 Rep Power: 9 This is the link to the bug-report: https://bugs.openfoam.org/view.php?id=134 However, I never got correct pressure values with this change.

August 13, 2017, 04:57
Fix-porousSimpleFoam
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karundev
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Quote:
 Originally Posted by sepp.zell This is the link to the bug-report: https://bugs.openfoam.org/view.php?id=134 However, I never got correct pressure values with this change.

 August 14, 2017, 04:50 #19 New Member   Sebastian Join Date: Feb 2017 Posts: 22 Rep Power: 9 You can follow the instructions here to compile a new solver: https://openfoamwiki.net/index.php/H...ure_to_icoFoam In your case copy porousSimpleFoam and replace the mentioned line of the solver as explained in the bug report. manuc likes this.

August 18, 2017, 03:41
#20
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karundev
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Quote:
 Originally Posted by sepp.zell You can follow the instructions here to compile a new solver: https://openfoamwiki.net/index.php/H...ure_to_icoFoam In your case copy porousSimpleFoam and replace the mentioned line of the solver as explained in the bug report.

sorry , i am new to openfoam. Please tell me where to copy this (means which file and where in file)

thank you