I've been working on a wall-bounded flow case in a 3D pipe. The problem is as follow:
-Inlet: 0.85 m/s
-Outlet Pressure: 10,000 Pa
-Steady-state with gravity included as a body force.
When I first ran the problem I encountered an issue with flow reversal at the outlet (Very annoying!) and this is how I resolved it:
1. Make sure that the outlet is far enough from the inlet. I recommend 10 x Hydraulic diameter from the inlet (at least)
2. If a body force is added and operating density is checked, make sure to start with the right operating density value in the cell zone condition although Fluent would calculate it automatically and also have a sound operating pressure reference.