CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   OpenFOAM Running, Solving & CFD (http://www.cfd-online.com/Forums/openfoam-solving/)
-   -   what do global and cumulative terms in continuity refer to exactly? (http://www.cfd-online.com/Forums/openfoam-solving/111663-what-do-global-cumulative-terms-continuity-refer-exactly.html)

immortality January 12, 2013 04:55

what do global and cumulative terms in continuity refer to exactly?
 
at results there are 3 types of residuals of continuity equation.whats the definition of them and difference?if cumulative and or global be negative whats wrong in the problem?

fumiya January 13, 2013 06:17

For the solvers of incompressible fluid, take a look at the
src/finiteVolume/cfdTools/incompressible/continuityErrs.H:

Code:

    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;

From the above definitions, the difference between the local and global
continuity error is whether the magnitude of divergence is taken or not.
The "local" error is a measure of the continuity of each cell and the
"global" error represents the continuity in the whole computational domain.
If the global error converges to zero, I think the negative value is of no matter.

I have no idea about the importance of considering the cumulative error.

Fumiya

immortality January 16, 2013 10:15

thanks fumiya
I cant grasp how the total continuity is calculated.my case is compressible.
What does mean cumulative continuity error?
Any hint is accepted here!


All times are GMT -4. The time now is 11:14.