fvc::flux(a,b,scheme) and -fvc::flux(-a,b,scheme) 's difference

sharonyue · April 24, 2015, 06:29

Hi guys,

In twoPhaseEulerFoam's alpha code. we have:

Code:

surfaceScalarField alphaPhic1
            (
                fvc::flux
                (
                    phic,
                    alpha1,
                    alphaScheme
                )
              + fvc::flux
                (
                    -fvc::flux(-phir, scalar(1) - alpha1, alpharScheme),
                    alpha1,
                    alpharScheme
                )
            );

Shouldn't it be the same with:

Code:

surfaceScalarField alphaPhic1
            (
                fvc::flux
                (
                    phic,
                    alpha1,
                    alphaScheme
                )
              + fvc::flux
                (
                    fvc::flux(phir, scalar(1) - alpha1, alpharScheme), //no minus minus here!
                    alpha1,
                    alpharScheme
                )
            );

Is there some tricky to do this in OpenFOAM? for some numerical considerations?

Thanks guys!!!

schröder · April 24, 2015, 06:51

It may be the same for some schemes.
At least for upwind schemes -flux(-phi)!=flux(phi).

sharonyue · April 24, 2015, 08:04

Quote:

Originally Posted by schröder

It may be the same for some schemes.
At least for upwind schemes -flux(-phi)!=flux(phi).

Um, quite clear....a good hint. haha. Let me dig it deeper. thanks.

April 24, 2015, 06:29	fvc::flux(a,b,scheme) and -fvc::flux(-a,b,scheme) 's difference	#1
sharonyue Senior Member Dongyue Li Join Date: Jun 2012 Location: Beijing, China Posts: 848 Rep Power: 18	Hi guys, In twoPhaseEulerFoam's alpha code. we have: Code: surfaceScalarField alphaPhic1 ( fvc::flux ( phic, alpha1, alphaScheme ) + fvc::flux ( -fvc::flux(-phir, scalar(1) - alpha1, alpharScheme), alpha1, alpharScheme ) ); Shouldn't it be the same with: Code: surfaceScalarField alphaPhic1 ( fvc::flux ( phic, alpha1, alphaScheme ) + fvc::flux ( fvc::flux(phir, scalar(1) - alpha1, alpharScheme), //no minus minus here! alpha1, alpharScheme ) ); Is there some tricky to do this in OpenFOAM? for some numerical considerations? Thanks guys!!!

April 24, 2015, 06:51		#2
schröder New Member Martin S. Join Date: Apr 2015 Posts: 9 Rep Power: 11	It may be the same for some schemes. At least for upwind schemes -flux(-phi)!=flux(phi). EngMec likes this.

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