Pressure outlet boundary condition

lxlylzl · February 20, 2018, 13:43

Dear all

In fluent, for outlet, I use pressure outlet with a defined gage pressure. For backflow, I use normal to the boundary method. So, for pressure outlet defined above, is it a mixed condition of Dirichlet condition and Neumann condition?

Any reference to the above would mean a lot to me. I work on Swirling flow.

I look forward to your response.

Regards,
Kukka

LuckyTran · February 20, 2018, 14:41

The pressure outlet boundary condition is indeed a mixed-like boundary condition (when there is reversed flow).

If there is no backflow then the pressure outlet applies the pressure to all cells and it behaves like a Dirichlet BC.

If there is reversed flow (or backflow) for some cells then you need to supply information for what is coming in. For those cells where there is reversed flow, it is some kind of inlet and you have several options for how to constrain this reversed flow. However, you can't control which cells have reversed flow or not so that this is not really a mixed BC either. You are able to fix the pressure but you can only constrain the velocity. So it's like a mixed BC but not really.

lxlylzl · February 21, 2018, 03:49

Dear LuckyTran,

Thanks a lot for the explanation. It was useful for me.

Regards,
Kukka

February 20, 2018, 13:43	Pressure outlet boundary condition	#1
lxlylzl Member Join Date: Jul 2012 Posts: 49 Rep Power: 13	Dear all In fluent, for outlet, I use pressure outlet with a defined gage pressure. For backflow, I use normal to the boundary method. So, for pressure outlet defined above, is it a mixed condition of Dirichlet condition and Neumann condition? Any reference to the above would mean a lot to me. I work on Swirling flow. I look forward to your response. Regards, Kukka

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February 20, 2018, 14:41		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 66	The pressure outlet boundary condition is indeed a mixed-like boundary condition (when there is reversed flow). If there is no backflow then the pressure outlet applies the pressure to all cells and it behaves like a Dirichlet BC. If there is reversed flow (or backflow) for some cells then you need to supply information for what is coming in. For those cells where there is reversed flow, it is some kind of inlet and you have several options for how to constrain this reversed flow. However, you can't control which cells have reversed flow or not so that this is not really a mixed BC either. You are able to fix the pressure but you can only constrain the velocity. So it's like a mixed BC but not really.

February 21, 2018, 03:49		#3
lxlylzl Member Join Date: Jul 2012 Posts: 49 Rep Power: 13	Dear LuckyTran, Thanks a lot for the explanation. It was useful for me. Regards, Kukka