Well, actually I have very similar problems as Ramesh does. Mine is steady, incompressible, Poiseulle-Couette flow with Re=100. Uniform flow in and fully developed flow out with no information on Pressure; pressure at exit is not given. The problem is that the axial velocity profile at exit is decreasing as the length of the pipe is getting longer; 10% error. One of the things that I suspect is the mass is decreasing from the inlet to exit. Also, have to keep relaxation factor for velocities very small like less than 0.1. Surprisingly, results are really good with 0.01. However, I have no idea why. I looked at my codes very carefully again and again, but everything looks fine. I appreciate any comments.

Ambrose

The pressure should be given at outlet, or at inlet.

The velocity at inlet is uniform or parabolic is fine. Jack

Thanks, Jack. My understanding on SIMPLER is that pressure is extracted from the velocity field such that pressure along the boundary is not necessary. Do I have to put in exact pressure at exit?

It is not necessary to set the pressure with SIMPLE algorithm. Under relaxation factor at about 0.2 should give good results if orthogonal grids are used. For your case, something may be wrong with implementation of the boundary conditions. Please carefully check if there are any bugs in your code, also check if the mass at the exit is fully conserved.

Fahong