# initial residuals in icoFoam

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 December 12, 2014, 09:55 initial residuals in icoFoam #1 Member   Mehrez Join Date: Nov 2012 Location: Bordeaux, France Posts: 80 Rep Power: 6 Hi, My question is about the icoFoam solver (used for transient incompressible Newtonian fluids). Does someone know how the initial residual is evaluated ? I mean the equation. Thank you in advance. Mhrz

 December 13, 2014, 03:29 #2 Senior Member   T Chourushi Join Date: Jul 2009 Location: India Posts: 319 Blog Entries: 1 Rep Power: 10 Have a look at the following post, where you will find that L1 norm is used. Residual definition of OpenFoam - Best Regards! Mehrez likes this.

December 14, 2014, 14:24
#3
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Mehrez
Join Date: Nov 2012
Location: Bordeaux, France
Posts: 80
Rep Power: 6
Quote:
 Originally Posted by Tushar@cfd Have a look at the following post, where you will find that L1 norm is used. Residual definition of OpenFoam - Best Regards!
Hi,
It is mentioned on the OpenFoam doc that "the residual is evaluated by substituting the current solution into the equation and taking the magnitude of the difference between the left and right hand sides".
So if I understand well, from the PCG.C file where
solverPerf.initialResidual() = gSumMag(rA)/normFactor
The (rA) is the difference between the left and right hand sides of the equation to solve ?
If we consider the IcoFoam solver. At which step of the PISO algorithm the residual is computed ?
You can see here the numbered equations :
https://www.dropbox.com/s/m848engmee4qawy/Algo.pdf?dl=0
Can you please based on the this file tell me the complete formula of the residual ?

Mhrz

 Tags icofoam, openfoam, residuals

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