I think that my implementation of the source terms is incorrect. In order to see that, considering my model (UDRGM + UDS) ,I have set the diffusion coefficient D=1e-15 and I have included the diffusion term as a source term. The result is that the solver blows up after some iterations I have considered the easy implementation of the laplacian (apply the gradient two times), as well as the recommended approach given at Solution #2057524. I (laplacian2) without success.nWhat can I do? I have tried one thousand things. I am aware of the fact that I can make mistakes with the implementation of the source term with the VOF method (as it requires the definition of subdomains for the phases, and so on), but in the case of my model ((UDRGM + UDS) everything is easy. I have no control of the code, as Fluent is basically a box, so I do not know what to do.n