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-   -   ncorr and nNonOrthCorr (http://www.cfd-online.com/Forums/openfoam/94664-ncorr-nnonorthcorr.html)

 zakir hussain November 22, 2011 09:52

ncorr and nNonOrthCorr

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<int>("nCorrectors", 1);

const int nNonOrthCorr =
pisoDict.lookupOrDefault<int>("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

 nimasam November 25, 2011 02:53

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!

 zakir hussain November 25, 2011 22:16

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

 sam1364 November 25, 2011 23:42

wallfunction

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 (Post 333515) 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!

 nimasam November 26, 2011 06:10

Quote:
 Originally Posted by zakir hussain (Post 333608) 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

 nimasam November 26, 2011 06:16

Quote:
 Originally Posted by sam1364 (Post 333614) 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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