[zakir hussain]

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]

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]

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]

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

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!

[nimasam]

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

[nimasam]

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:

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