"Residuals" in residualControl

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"Residuals" in residualControl

Posted December 4, 2016 at 17:54 by kindle

PimpleFoam hahhahhhahha

Quote:

Originally Posted by knuckles

In system/fvSolution, I can specify tolerances on matrix solvers:

Code:

solvers
{
    p
    {
        solver         PGC;
        preconditioner DIC;
        tolerance      1e-08;
        relTol         0;
    }
}

My understanding is that openfoam will construct an equation of the form Ax = b, solve it in some iterative way, and will stop iterating when the residual, |Ax - b|, is less than 1e-08 (relTol = 0 so it is not a factor here).

With SIMPLE/PIMPLE, it's also possible to specify a residualControl:

Code:

PIMPLE
{
    nOuterCorrectors  50; 
    nCorrectors        3;
    nNonOrthogonalCorrectors 3; 

    residualControl
    {
        U
        {
            tolerance 1e-3;
            relTol       0;
        }
        p
        {
            tolerance 1e-2;
            relTol       0;
        }
    }
}

The code above means that the "outer" PIMPLE loops will continue until either

50 (nOuterCorrectors) loops have been completed
The residuals of both U and p fall below the specified values

I'm unclear on which "residuals" are considered here. If they are the same variety as described above, then it seems to me that setting residualControl tolerances which are more generous than the solver tolerances should give only one pimple loop. My test cases show that this is not how this works.

I assume that the residuals being considered here quantify, in some way, how well the pressure/momentum coupling is being resolved. Does anyone know which residuals are considered here?

Posted in Solver

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