[Zhanyuan Wang]

Hello foamers,

I want to add a set of scalar transport equation (consists of two equations) in VOF model (compressibleInterFoam). Here I call them Y1Eqn and Y2Eqn, where Y1 and Y2 are iterative variables. These two equations need to be solved in different phase area separately, that is to say, Y1Eqn is solved and Y2Eqn is set to zero when the value of volScalarField alpha1 is not zero (which means the 1st phase), and the same operation is done in the 2nd phase. The thought of such equations is listed in attachment below.

So is there anyone who can tell me how can I achieve this goal?

I thought up a solution but i dont know whether it is right. Firstly i multiplied the equation with alpha1, something like:

fvScalarMatrix Y1Eqn
(
alpha1*(fvm::ddt() + fvm:: () - fvm::laplacian() + source term)
)

but when i run the case it broke up at the first time step. Later i find the problem: it is not allowed to multiply fvm terms with a field whose value has the probability of being zero, and volScalarField alpha1 is exactly such a field(But i dont know why it is not allowed, anyone can explain it to me?). So I modified my equation later on by changing the fvm terms to fvc terms, something like:

fvScalarMatrix Y1Eqn
(
fvm::ddt() + alpha1*fvc:: () - alpha1*fvc::laplacian() + source term
)

I m not sure the influence of using fvc instead of fvm in convection terms and diffusion terms and what is the difference between these two methods. Can i achieve my goal by this method? Can anyone explain it to me?

I am sincerely grateful for anyone who can offer any information. Thanks very much.