I would like to simulate the flow in a circular pipe with a turbine in the pipe. [ I did not model the streamline disturbance by the turbine, I model the turbine as the subdomain with a momentum sink] I specify the inlet boundary condition of the pipe as "Inlet" with a given x-component velocity. For an outlet boundary condition, I think I should specify "Outlet" with an x-component velocity as v2 = rho1*v1/rho2. This v2 comes from the continuity equation for 1D flow. However I saw that in the tutorial about "flow through a butterfly valve" and "flow in a catalytic converter" of CFX, they are all specified the zero relative pressure as the outlet boundary condition. 1. I was wondering about zero relative pressure that when do we use this boundary condition? Should I use it in my case? 2. In "flow in a catalytic converter", I note that it's emphasized that the outlet boundary condition must be static pressure, not average static pressure. Do anyone know why? Thank you very much.

Atit

In additon, when I set zero total pressure at the inlet of the pipe, what does it mean? When should we use this condition? Thank you.

Atit Koonsrisuk

all the boundary conditions and their meanings have been documented in the USER MANUAL. Please refer to them!!

regards!!