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 June 9, 2013, 06:02 programming & icoFoam #1 Senior Member   Sasan Ghomi Join Date: Sep 2012 Location: Iran - Tehran Posts: 185 Rep Power: 6 Hi foamers , what is the relation between non-orthogonality in the grid and number of solving P.Equ ??? please take a look at this part of icoFoam : PHP Code: ``` for (int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++)            {                fvScalarMatrix pEqn                (                    fvm::laplacian(rUA, p) == fvc::div(phi)                );                pEqn.setReference(pRefCell, pRefValue);                pEqn.solve();                if (nonOrth == nNonOrthCorr)                {                    phi -= pEqn.flux();                }            }  ``` why the number of solving P.Equ should be equal nNonOrthogonalCorrectors ?? I think in PISO algorithm the number of solving pressure equation should be equal nCorrectors. I think nNonOrthogonalCorrectors is related to quality of grid generation. what is the relation between grid's quality and number of solving pressure equation?? Can anyone clarify this issue for me ? Thanks and best regards, Sasan.

 June 9, 2013, 15:27 #2 Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 9,820 Blog Entries: 39 Rep Power: 108 Hi Sasan, Does this answer your questions: http://openfoamwiki.net/index.php/IcoFoam ? Best regards, Bruno __________________ OpenFOAM: FAQ | Getting started Forum: How to get help, to post code/output and forum guide What am I doing/planning: blog/wiki Read this before sending me PM

 June 9, 2013, 16:51 #3 Senior Member   Sasan Ghomi Join Date: Sep 2012 Location: Iran - Tehran Posts: 185 Rep Power: 6 Hi Bruno, Thanks for your reply. I want to know that why the quantity of solving pressure equation is equal to quantity of nNonOrthogonalCorrectors ? Thanks and best regards, Sasan.

 June 9, 2013, 17:33 #4 Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 9,820 Blog Entries: 39 Rep Power: 108 Hi Sasan, I'm not sure I understand you correctly... are you asking about the following code? Code: ```if (nonOrth == nNonOrthCorr) { phi -= pEqn.flux(); }``` edit: or is it about: Code: `for (int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++)` Best regards, Bruno __________________ OpenFOAM: FAQ | Getting started Forum: How to get help, to post code/output and forum guide What am I doing/planning: blog/wiki Read this before sending me PM Last edited by wyldckat; June 9, 2013 at 17:34. Reason: see "edit:"

 June 10, 2013, 02:31 #5 Senior Member   Sasan Ghomi Join Date: Sep 2012 Location: Iran - Tehran Posts: 185 Rep Power: 6 Hi Bruno, I am asking about : Code: `for (int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++)` Thanks and best regards, Sasan.

June 10, 2013, 07:24
#6
Super Moderator

Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 9,820
Blog Entries: 39
Rep Power: 108
Hi Sasan,

Well, as the wiki page explains:
Quote:
 Originally Posted by http://openfoamwiki.net/index.php/IcoFoam // iteratively correct for non-orthogonality. The non-orthogonal part of the Laplacian is calculated from the most recent // solution for pressure, using a deferred-correction approach.
Any explanation beyond this (that I could find) is on this thesis:
Quote:
 Originally Posted by http://openfoamwiki.net/index.php/IcoFoam Hrvoje Jasak, PhD 1996, PDF of thesis posted at: Error analysis and estimation in the Finite Volume method with applications to fluid flows.
... which I don't have time to read and study .

Best regards,
Bruno
__________________

 August 25, 2013, 23:55 #7 Senior Member   Dongyue Li Join Date: Jun 2012 Location: Torino, Italy Posts: 750 Rep Power: 9 Hi , http://www.cfd-online.com/Forums/ope...tml#post447985 I think this will make it clear. It is related to quality of grid generation and the non-orthogonal correction in the diffusion term, you can dig it in page.83 of Jasak's thesis. wyldckat likes this.

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