Hi, Karthik Thanks for your reply again. FYI, I have increased the viscosity of the solid phase 10^5 times higher than the liquid phase using UDF. The viscosity of the fluid is in the order of 10^-5 (in SI units)and viscosity of the solid taken as 1. And you are right, I was having stability issues for all other types of meshes except polyhedral meshes. If, I try to increase mushy zone constant more than 10^7 or 10^8, the continuity was diverging. What do you suggest regarding viscosity data should I use for solid and liquid phase ?