[user]

Hello foamers,


I'm struggling with adding a heat source via scalarCodedSource because it seems that negative values are needed to have a positive source.

For further investigations I made a simple test case with rhoPimpleFoam where I used a scalarSemiImplicitSource in a cellZone to define a positive heat source in a closed system:

heatSource1
{
    type            scalarSemiImplicitSource;
    active          true;
 
    scalarSemiImplicitSourceCoeffs
    {
        selectionMode   cellZone; // all, cellSet, cellZone, points
        cellZone        sourceZone;
        volumeMode      absolute;
        injectionRateSuSp
        {
            h   (0.1 0);
        }
    }
}

and additionally a scalarCode which simply reads out the eqn.source() and printing the sum of it:

heatSource2
{
    type            scalarCodedSource;
    active          true;
    name            heatSource2; 
   
    scalarCodedSourceCoeffs
    {
        selectionMode   cellZone;
        cellZone        sourceZone;
        fields          (h); 

        codeInclude
        #{
        #};

        codeCorrect
        #{
        #};

        codeAddSup
        #{
            scalarField& hSource = eqn.source();
            
            const scalarField& V = mesh_.V();     
            double hSourceTot = 0;

            forAll(V, i)  
            {
                hSourceTot += hSource[i]; 
            }
            Pout << " hSourceTot = " << hSourceTot << " with dimension " << eqn.dimensions() << endl; 
                       
        #};

        codeConstrain
        #{
        #};            

        code
        #{
            $codeInclude
            $codeCorrect
            $codeAddSup
            $codeSetValue
        #};
    }
    
}

In the above case the toal sum of the heat sources are "-0.1" - a negative value. Could somebody explain why sources in scalarCodedSources must be negative? Is this specific to the energy equation?

I tested it with OpenFOAM-v2006 and v2012 and have attached the test case. Just unpack and run "./runMesh" and after that rhoPimpleFoam

Thanks in advance
Ulf

[mAlletto]

If I'm not mistaken, the function below gives you a reference to the source of the whole equation (the term on the right hand side the equation . If you are solving the temperature equation there is not only coded source in it but a lot more staff. Think about the laplacian discretization on non ortognonal grids. There you get also explicit source term.

eqn.source();

[user]

Yes, thanks for your reply - your are absolutely right and I also thought about this. That's why I tested it without the scalarSemiImplicitSource and then the reported sources from scalarCodedSource is zero.



Any ideas? I also looked at the code and couldn't find any difference (regarding the sign) between scalarCoded and scalarSemiImplicit. Maybe some C/C++ expert could analyse this ;-)

[zhenFoam]

Hello, everyone

I'm stuck with the same problem. Can someone please explain?

1. why sources in scalarCodedSources must be negative?

2. why sources in scalarCodedSources always multiply by voluMe V[i] ?

[Tibo99]

Hi,

This maybe could answer your question #2 (see picture in attachment).

I don't have the answer for your 1st question though. I encounter the same question and don't have the answer yet.

If someone can answer this one, it would be appreciated.

Best Regards,

[mAlletto]

the answer to queston 2 is that if you discretize a source term in a fine volume framework you integrate it over the cell volume. For a source term which is constant in the volume (this is the usual assumption made) you have to multiply it by the cell volume

[zhenFoam]

I got it! Great thanks for your reply @Tibo99, @mAlletto

Could somebody explain the queston 2: why sources in scalarCodedSources must be negative?

[Tibo99]

You mean question 1?

[zhenFoam]

Yes, I mean question 1. Sorry for the type error.

[mAlletto]

Can you formulate your question a bit more clearly?

[sharonyue]

I run into this problem today. I did some research. I think its because of the following:

code.template<class Type>
Foam::tmp<Foam::fvMatrix<Type>> Foam::operator==
(
    const fvMatrix<Type>& A,
    const fvMatrix<Type>& B
)
{
    checkMethod(A, B, "==");
    return (A - B);
}