[jagan1mohan]

Hello fiends, foamLog creates three text files for continuity equation in openFOAM.


1. What is the difference between local, global and cumulative continuity errors?



How to judge convergence, (besides residuals from governing equations solved)?


Thank you,
Jagan Mohan

[tas38]

For incompressible flows:

volScalarField contErr(fvc::div(phi));

    scalar sumLocalContErr = runTime.deltaTValue()*
        mag(contErr)().weightedAverage(mesh.V()).value();

    scalar globalContErr = runTime.deltaTValue()*
        contErr.weightedAverage(mesh.V()).value();
    cumulativeContErr += globalContErr;

    Info<< "time step continuity errors : sum local = " << sumLocalContErr
        << ", global = " << globalContErr
        << ", cumulative = " << cumulativeContErr
        << endl;

Local appears to be:



Global:



and cumulative is the sum of the global continuity error over the total number of time steps.

[M.Davoodi]

Hi everyone,

Lately I have been working on an algorithm for a two-phase solver to couple the pressure and velocity fields. The method is Similar to PC_SIMPLE algorithm if you have heard about it (something like a phase coupled SIMPLE algorithm) ….

I believe that I have modified the pEqn.H file correctly, but I feel I am missing something obvious somewhere, as once I look at the time step continuity errors, my local error is always much larger than the global error:

"
time step continuity errors for sum local = 1.74033576902e-07, global = -9.93993329672e-21, cumulative = -8.2037380338e-16

"

Interestingly, the simulation doesn't diverge but my local error never gets smaller than 1e-7 which is a bit odd for me.

Does anyone have any idea why this might be happening? I have a feeling that it should be something small and obvious that I am missing here ….

Cheers,
Mahdi