# ncorr and nNonOrthCorr

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 November 22, 2011, 09:52 ncorr and nNonOrthCorr #1 Member   zakir Join Date: Nov 2011 Posts: 43 Rep Power: 5 hello everyone when i am reading the icoFoam.c,I feel confused with it. It said that "include 'readPISOcontrols.H'"and I found the file which defined the number like this: const int nCorr = pisoDict.lookupOrDefault("nCorrectors", 1); const int nNonOrthCorr = pisoDict.lookupOrDefault("nNonOrthogonalCorre ctors", 0); I think it doesn't fit very case. my question is how to decide the nCorr and nNonOrthCorr. Are there any relative theories about this? I have read jasak's phd, but I didn't find the answer. Thank you very much. Best Regards! zakir

 November 25, 2011, 02:53 #2 Senior Member   Nima Sam Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,123 Blog Entries: 1 Rep Power: 14 whats your mean by "decide the nCorr and nNonOrthCorr" ? you can define these values in your case directory at system/fvSolution lookupOrDefault : if you define a value in your fvSolution file then it chooses that value and if you dont define the value, solver considers it as default number which is 1 for nCorr and 0 for nNonOrthCorr. usually 2,3 times of corrections are usually enough for piso Algorithm so ( nCorr = 2, 3 ) but for non-orthogonality depends on your mesh and how much non orthogonal it is!

 November 25, 2011, 22:16 #3 Member   zakir Join Date: Nov 2011 Posts: 43 Rep Power: 5 thanks to nima. I have make clearly about ncorr. I know that the non-orthogonality depends on my mesh,but I don't know what it means "how much non orthogonal it is".Could you please give me a detailed explaination about deciding the nNonOrthCorr on a non-orthogonal mesh? thank you very much

November 25, 2011, 23:42
wallfunction
#4
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pooyan
Join Date: Nov 2011
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Hi Nima,

I have a question from you.
I am now solving cavity problem in 3D. for turbulence model, I selected RANS and k-epsilon. for wall function, I selected nutkwallfunction. However, I could not find the procedure (how the wall function is defined) used in this type of wall function. I would be grateful if you could tell me what specific wall function is used in nutkwallfunction.

Thanks,
Pooyan

Quote:
 Originally Posted by nimasam whats your mean by "decide the nCorr and nNonOrthCorr" ? you can define these values in your case directory at system/fvSolution lookupOrDefault : if you define a value in your fvSolution file then it chooses that value and if you dont define the value, solver considers it as default number which is 1 for nCorr and 0 for nNonOrthCorr. usually 2,3 times of corrections are usually enough for piso Algorithm so ( nCorr = 2, 3 ) but for non-orthogonality depends on your mesh and how much non orthogonal it is!

November 26, 2011, 06:10
#5
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Nima Sam
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Quote:
 Originally Posted by zakir hussain thanks to nima. I have make clearly about ncorr. I know that the non-orthogonality depends on my mesh,but I don't know what it means "how much non orthogonal it is".Could you please give me a detailed explaination about deciding the nNonOrthCorr on a non-orthogonal mesh? thank you very much
i dont know but i think there is no special explanation for it you can find it by try and error

November 26, 2011, 06:16
#6
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Nima Sam
Join Date: Sep 2009
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Quote:
 Originally Posted by sam1364 Hi Nima, I have a question from you. I am now solving cavity problem in 3D. for turbulence model, I selected RANS and k-epsilon. for wall function, I selected nutkwallfunction. However, I could not find the procedure (how the wall function is defined) used in this type of wall function. I would be grateful if you could tell me what specific wall function is used in nutkwallfunction. Thanks, Pooyan
hi dear pooyan
please next time , open new thread or post ur question in related topic
however for k-epsilon look at userguide page-41 or in brief:

Code:
```kappa = 0.5U*U*
epsilon = C^0.75 kappa^1.5 / l
C = 0.09
l = characteristic length```

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