[swapnil313]

I have two outlets at atmosphere exits.
How can I add pressure boundary conditions ?
I'm confused about the reference/static/total pressure settings.

[ghorrocks]

What do you mean by "add pressure boundary conditions"?

Total pressure: https://en.wikipedia.org/wiki/Total_pressure
Static pressure: https://en.wikipedia.org/wiki/Static_pressure

Reference pressure is used by CFX to reduce numerical round-off errors. For instance if a 1 Pa pressure difference exists in a body at 1 bar absolute pressure:

* If the reference pressure is 0, then the pressure difference is 100001 [Pa] - 100000 [Pa] which is of course a 1 [Pa] difference, but if the numerics are only accurate to 4 significant figures you get 1.000e5 [Pa] - 1.000e5 [Pa] and the 1 [Pa] pressure difference has disappeared. A simulation based on this would have unexpected results as it cannot resolve the pressure variations. This effect is called round-off error.

* If the reference pressure is 1 [bar], then the pressure difference is 1 [Pa] - 0 [Pa] which is of course a 1 [Pa] difference. Now if we consider numerics which is only accurate to 4 significant figures you get 1.000e0 [Pa] - 0.000e0 [Pa] and the 1 [Pa] pressure difference is still resolved. A simulation based on this would can work as the 1 [Pa] pressure difference is accurately resolved, despite the limited accuracy of the numerics.