How to apply Neumann Boundary Conditions in Star-CCM+
 

As mentioned in the title, I'm trying to apply Neumann BC or derivative BC to a STAR-CCM simulation and not really finding much on the internet. The simulation is air flowing through a tube.

Thanks!!

You mean - to set up a derivative on the boundary? - Like this:
https://wikimedia.org/api/rest_v1/me...32212ab5db4ea3

For which variable?

It looks like the flux?

Exactly. Just wanted to clarify - "flux" of what.

Velocity. It was suggested to me but I'm not sure if I entirely understand what I'm doing yet. Currently simulating air flow in a large tube 1.5 m dia tube with atmospheric pressure at the inlet and outlet.

Something is missing in your task description: you cannot have zero pressure drop while having the flow of air in the pipe, unless it's an inviscid approach.

I have an inlet velocity of 20 m/s, so the momentum of the air is carrying it through the tube.

Then you can just set the velocity inlet boundary condition (± extrusion for boundary layer development depending on the task) at inlet and pressure outlet on another side.

Where does Neumann BC come from?