[danny123]

Hello,

I want to add a term in alpha1Eqn in interFoam to ensure that this equation is solved when there is a gradient in alpha1. Reason: if there is no gradient, only the mass balance needs to be solved, the specy balance is not relevant.

I looked at the code for alpha1Eqn:

fvScalarMatrix alpha1Eqn
        (
            #ifdef LTSSOLVE
            fv::localEulerDdtScheme<scalar>(mesh, rDeltaT.name()).fvmDdt(alpha1)
            #else
            fv::EulerDdtScheme<scalar>(mesh).fvmDdt(alpha1)
            #endif
          + fv::gaussConvectionScheme<scalar>
            (
                mesh,
                phi,
                upwind<scalar>(mesh, phi)
            ).fvmDiv(phi, alpha1)
        );

This is in OpenFoam 2.3.x. The 2nd term is the divergence of (alpha1 phi) I understand. In order to cancel this term out in case of not changing alpha1, I want to substract alpha1 x divergence (phi). The last term will be zero if continuity is fulfilled, so the result should be the same once the whole equation system is solved.

If this would be a simple vector operation, this would be easy. However alpha1 is the unknown variable of the equation system.

I tried

- alpha1*fv::gaussConvectionScheme<scalar>
            (
                mesh,
                phi,
                upwind<scalar>(mesh, phi)
            ).fvmDiv(phi)
        );

which obviously does not work. Divergence is coded in p_rghEqn as

fvc::div(phiHbyA)

but I need to put the variable upfront. Is there anybody who knows how to do this?

Regards,

Daniel

[danny123]

Found the solution:

          - fvc::div(phi)*fvm::Sp(1,alpha1)

Works as expected.