Karthik R
Hello,nZero Gradient generally means that the normal derivative is 0. nRegarding your question on the inlet - please look into a basic finite volume textbook such as Numerical Heat Transfer and Fluid Flow by Suhas Patankar.This should give you information on all the basics of CFD.Basically,when you are applying these boundary conditions,you are reformulating the conservation equations across half the cell near your boundary.Please have a look at these basic CFD books and they would give you the details.nKarthikn