how to set Bpondary conditions at the outlet

Aly

I am simulating water flow in a vertcial pipe. the Boundary Conditions are: pressure outlet (at exit) open to atmosphere, velocity inlet (from bottom)0.5 m/s,reference pressure location at the top/exit.

I have done some single phase (water) simulation in which I calculated the area wt average of velocity along lines made with the help of surface\line command across the diameter of the pipe at different heights from the base.The water velocity on the line at the exit is coming lower than inlet (0.5m/s) i.e from inlet the velocity gradually forming a parabolic profile and than at exit it drops to 0.457m/s. In a XY plot of velocity at these various lines along the height i see developing parabolic velocity profile except that the top most line which is on the exit shows a scatter of values between 2 to 5.6 m/s.

suggestions are needed. thanks