Thank You! Your advice is absolutely correct, however when I change the mass flow rate at the inlet, now my calculation is not converged at all, even I try many methods and also I did it with the coarse mesh. Many people pointed out that when the solution is not converged, it is because of the mesh quality and the boundary condition, and I already checked with these things. I still could not get the convergence of solution even I gave 10000 iterations. Can you guide me more? Thank You!n