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How to update phi in Fractional Step Method

Hi Foamers,

I intend to realise a semi-implicit fractional step in OpenFOAM but got stuck at the final step where the flux phi is updated. Please see the code here:

Code:

// Create Poisson Matrix

    fvScalarMatrix pEqn

    (

        fvm::laplacian(p)

    );

    pEqn.setReference(pRefCell, pRefValue);



// PressureCorrection.H 

    solve(pEqn==fvc::div(U)/runTime.deltaT());

    phi -= pEqn.flux();// This is where I have problem.

    U -= runTime.deltaT()*fvc::grad(p);

    U.correctBoundaryConditions();

According to Jasak, if there is a plus sign before laplacian (p) then it should be:

Code:



    phi -= pEqn.flux();

otherwise it should be

Code:



    phi += pEqn.flux();

However, I cannot get very good mass conservation from both of them. Or there are other ways to update flux? PS: I am solving momentum equation implicitly using second order backward.

Thanks for your help,

Carlen

Quote:

Originally Posted by Carlen (Post 641886)

Hi Foamers,

I intend to realise a semi-implicit fractional step in OpenFOAM but got stuck at the final step where the flux phi is updated. Please see the code here:

Code:

// Create Poisson Matrix

    fvScalarMatrix pEqn

    (

        fvm::laplacian(p)

    );

    pEqn.setReference(pRefCell, pRefValue);



// PressureCorrection.H 

    solve(pEqn==fvc::div(U)/runTime.deltaT());

    phi -= pEqn.flux();// This is where I have problem.

    U -= runTime.deltaT()*fvc::grad(p);

    U.correctBoundaryConditions();

According to Jasak, if there is a plus sign before laplacian (p) then it should be:

Code:



    phi -= pEqn.flux();

otherwise it should be

Code:



    phi += pEqn.flux();

Did you solve this problem?