Array , I am introducing a source term that gives the same equation as the one of a User-Defined-Scalar, being the scalar the liquid mass fraction. I have not dealt with convergence problems with the UDS equation, so I deduce that the same should apply to the VOF equation + diffusion term as a source, as they are the same equation. In any case, as far as I am concerned, a diffusion term always stabilizes the solution. This is essentially what is done in turbulence modeling, just increase the value of the diffusion term in the momentum and energy equation. nFurthermore, I do not see the point of simulating the volume fraction without diffusion (the one of VOF) with RANS turbulence models. These turbulence models are extremely diffusive, so all the instabilities that govern multiphase flows with Re, We 1 are lost. And for simple flows one can afford a mesh required by SBES, for example,nArray, the equation shown in Section 18.3.4 Volume Fraction Equation does not include any diffusion term. Is it a kind of stabilization term used by the solver?nBased on your comment, I deduce that ANSYS Fluent does not handle in the same way a pure diffusion term of the governing equations and a diffusion term included as a source term. Is there any way to adapt the source term in order to obtain the same result?n