[nimasam]

i have a two phase flow with variable density which change with pressure, temperature and chemical conversion!
look following step to derive a formulation for alphal1

1)ddt(rho) + div.(rho,U) = 0

and rho = rho1*alpha1+rho2*(1-alpha1)=(rho1-rho2)*alpha1+rho2

so:

2)ddt(rho_*alpha1) + div.(rho_,U) + ddt(rho2) + div.(rho2,U) = 0

and rho_ = rho1 - rho2

from MULESTemplates.C :

fvScalarMatrix psiConvectionDiffusion
(
fvm::ddt(rho, psi)
+ fv::gaussConvectionScheme<scalar>(mesh, phi, UDs).fvmDiv(phi, psi)
//- fv::gaussLaplacianScheme<scalar, scalar>(mesh, CDs, snGrads)
//.fvmLaplacian(Dpsif, psi)
- fvm::Sp(Sp, psi)
- Su
);

and from incompressibleInterFoam or interPhaseChangeFoam :
MULES::implicitSolve(oneField(), alphalpha1, phi, phiAlphalpha1, Sp, Su, 1, 0);

can i use rho_ instead of oneField() in above structure?

[gaza]

Yes you have to do it.