[sglm]

Hello,

In Ansys Fluent, I observed in some tutorials and videos from different sources that people generally use zero gage pressure boundary conndition for outlet. What is the appropriateness of using this constant pressure outlet boundary condition?

Thank you.

[jeytsav]

Hello and welcome to the forum,

First of all I would recommend to use a more representative title for your future posts. This will help other members quickly identify whether they can assist you or not and it will increase your chances of receiving a helpful answer.

So now regarding to your question, CFD problems need the specification of well-posed boundary conditions in order for the Navier-Stokes equations to be appropriately solved. It is common to use a Pressure Outlet condition with Gauge Pressure = 0 if we have no other information about what is happening there. For subsonic flows this would mean that the absolute pressure at the outlet would be equal to the Operating Pressure specified at the operating conditions toolbox. (P_absolute = P_operating + P_gauge). To avoid round-off error, Fluent uses only the Gauge pressure for all the calculations that take place.

You may also find the following post interesting:
Why we normally provide velocity at inlet and pressure at outlet for pipe flow?

Regards,
Ioannis