hi

for pipe flow, i set the inlet boundary as Velocity Inlet, and outlet boundary as Outflow, on the Initial Window i set compute from inlet boundary with initial gauge pressure = 13332Pa and x-velocity = 0.2m/s. Then i set the Outlet with flow rate weighting = 1. after simulated the pressure at the inlet(<>-75Pa) and outlet(-153Pa) shown in negatif value. what are the procedure and formula used to get the negatif value. The condition under simulated were laminar, steady, 2d, segregated solver and newtonian fluid.

In cfd software, you always use the relative pressure. So you could have a negative relative pressure with a positive pressure.