Karthik R
Hello,nHave you attempted to run the model without the UDF? Does it work?nAlso, I'd strongly recommend that you print the values of mu_t in your UDF. Use the Message statements. This will do two things: nIs the UDF working properly?nIs the magnitude of mu_t correct?nI don't see anything wrong with the UDF straightaway. I'm worried about the magnitude though (if it is too large or small depending on your initial conditions). nAlso, check your overall mesh quality and make sure that you have a good mesh.nKarthikn