What would be the most appropriate inlet and outlet boundary conditions for an incompressible steady state flow in a vertical tube. The flow rate is sought as part of the solution.

I tried inlet zero refernce pressure and a free fully developed oultlet condition but with no success.

Your kind response is appreciated.

For inlet: velocity is prescribed, pressure is extrapolated from interior, For outlet: Pressure is prescribed, velocities are extrapolated from interior. Try above BC.

Versi, You Kindly responded: "For inlet: velocity is prescribed, pressure is extrapolated from interior, For outlet: Pressure is prescribed, velocities are extrapolated from interior. Try above BC."

But I thought prescibing velocity at the inlet (or exit)implies prescibing the flow rate itself for such steady state simulation. I am looking for BC's that will lead to the flow rate as an output results not as an input. What do you suggest. Thanks