I understand thanks. After the re-meshing of pipe wall with the tet mesh, the solution converged. However, the continuity residual did not reach 0.001. So I don't know why Ansys Fluent indicated that the solution completed. Because even my 500 iteration mark was not reached. I thought in order for the solution to be marked as completed, either all residuals have to reach their convergence value or the iteration number has to be reached. In this case, neither occurred but solution completed. Does the below residual plot of continuity seem reasonable to you?