I want to use zero normal-derivative at exit. How can I do it in Phoenics code? I know it is defined as "OUTFLOW" condition in Fluent software.

Hello I has written a fortran code for solving navier stokes equations in triangular meshes by colocated finite volume methode. My program Converges but the conservation of mass in whole domain is not satisfied. I have applied some notes in Versteeg & Malalasekera's book, But in some geometries the problem remains.I think that relates to neuman boundary condition for velocities at outlet, and maybe there are some deficiencies in boundary conditions for pressure correction equation. It would be appreciated if you help me.