[Sylv]

Dear Foamer,

I have to add a source term in the momentum equation of my pimpleFoam solver (OpenFOAM 2.3.0). Therefore, I simply add a extra term to UEqu:

tmp<fvVectorMatrix> UEqn
(
    fvm::ddt(U)
  + fvm::div(phi, U)
  + turbulence->divDevReff(U)
== 
     fvc::Sp(someForce)   //this is the extra line
);

If I use "fvc::Sp", the source term is treated explicitly, meaning it is left in the right hand side of the linear system AU=B (in B...). If I use fvm::Sp, the source term is added to the matrix A (implicit source).

Nevertheless, in the file which defined fvc::Sp ($FOAM_SRC/finiteVolume/finiteVolume/fvc/fvcSup.H) there are three definition of a source: Sp, Su and SuSp. Sp is advertised as "implicite", Su=''explicite'' and SuSp="A mix of Sp an Su". Same in $FOAM_SRC/finiteVolume/finiteVolume/fvm/fvmSup.H

Question: what is then the difference between fvc::Sp and fvc::Su? They should both populate B of the linear system. Same question for fvm::Sp and fvm::Su.

Cheers,
Marcel