Pressure Outlet vs Outlet Vent BC

u2berggeist · September 3, 2018, 10:56

For boundary conditions, what are the differences between Pressure Outlet and Outlet Vent?

Besides the loss coefficient, I can't really think of another reason why the Vent would be used over the Pressure Outlet.

Main reason I ask is that I noticed that Fluent defaults to using the Outlet Vent BC instead of the seemingly more normal Pressure Outlet.

Am I missing anything?

LuckyTran · September 3, 2018, 14:12

Actually the Fluent default when nothing is specified is a wall. It's only an outlet vent depending on the mesher you used that assigned it as an outlet vent.

Pressure outlet imposes a uniform static pressure on the outlet boundary. The outlet vent is just an pressure outlet (i.e. ambient pressure) with a loss coefficient. But the pressure drop is only in the direction of the flow so you can end up with a non-uniform pressure at the boundary if you have a non-uniform velocity profile.

u2berggeist · September 3, 2018, 14:51

I think I figured out why it was "outlet-vent" was the default for my boundary conditions. The name of those cell zones started with "outlet". I'm guessing Fluent does some kind of simple regex for the first characters of the cell zone to determine the automatically-applied Boundary Condition.

Thanks for the clarification!

September 3, 2018, 10:56	Pressure Outlet vs Outlet Vent BC	#1
u2berggeist Member James Wright Join Date: Oct 2015 Posts: 40 Rep Power: 10	For boundary conditions, what are the differences between Pressure Outlet and Outlet Vent? Besides the loss coefficient, I can't really think of another reason why the Vent would be used over the Pressure Outlet. Main reason I ask is that I noticed that Fluent defaults to using the Outlet Vent BC instead of the seemingly more normal Pressure Outlet. Am I missing anything?

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September 3, 2018, 14:12		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,675 Rep Power: 66	Actually the Fluent default when nothing is specified is a wall. It's only an outlet vent depending on the mesher you used that assigned it as an outlet vent. Pressure outlet imposes a uniform static pressure on the outlet boundary. The outlet vent is just an pressure outlet (i.e. ambient pressure) with a loss coefficient. But the pressure drop is only in the direction of the flow so you can end up with a non-uniform pressure at the boundary if you have a non-uniform velocity profile.

September 3, 2018, 14:51		#3
u2berggeist Member James Wright Join Date: Oct 2015 Posts: 40 Rep Power: 10	I think I figured out why it was "outlet-vent" was the default for my boundary conditions. The name of those cell zones started with "outlet". I'm guessing Fluent does some kind of simple regex for the first characters of the cell zone to determine the automatically-applied Boundary Condition. Thanks for the clarification!