Pressure and Flow as Inlet Boundary Condition

ashtonJ · March 9, 2015, 21:10

Dear all,
I have volumetric flow rate and pressure at the inlet of my model.
I would like to apply both flow rate and pressure as inlet boundary condition in CFX Pre. Does any one know how this is doable.

Thank you.
AshtonJ

Lance · March 10, 2015, 03:36

You cannot specificy both pressure and velocity/flow rate on the same boundary.

PeMo · March 10, 2015, 04:08

However, you can set a Total Pressure and adjust the pressure level according to your required flow rate, right?

ashtonJ · March 12, 2015, 00:16

Thanks PeMo. Can you explain a bit more please, how do I know the pressure level corresponding to my flow rate.
Actually I was reading an article in which it was mentioned that in ANSYS Fluent volume flow rate and pressure both were applied as the inlet boundary condition. I wonder how it is possible to set two variables as inlet boundary condition either in Fluent or in CFX.

ghorrocks · March 12, 2015, 03:53

It is numerically impossible to define both the pressure and velocity at a boundary in subsonic flow. You can do this in supersonic boundaries.

If you have a steady state flow with an inlet and an outlet you simply apply the flow rate boundary to the inlet and the pressure boundary to the outlet or vice versa. Then you have specified the pressure and flow rate at a boundary - but the flow rate will only be as accurate as your imbalance convergence.

ashtonJ · March 15, 2015, 17:19

Thanks Glenn.
Actually I emailed the author of the article who claimed that he used both pressure and volume flow rate as inlet boundary condition.
He says that in ANSYS Fluent 14.5 they are able to set these two variables (pressure and volume flow rate) as the inlet boundary condition. Does this make sense to you?

ashtonJ · March 15, 2015, 17:21

And also their flow is subsonic.

March 9, 2015, 21:10	Pressure and Flow as Inlet Boundary Condition	#1
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Dear all, I have volumetric flow rate and pressure at the inlet of my model. I would like to apply both flow rate and pressure as inlet boundary condition in CFX Pre. Does any one know how this is doable. Thank you. AshtonJ

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March 10, 2015, 03:36		#2
Lance Senior Member Lance Join Date: Mar 2009 Posts: 669 Rep Power: 22	You cannot specificy both pressure and velocity/flow rate on the same boundary.

March 10, 2015, 04:08		#3
PeMo Member Peter Join Date: Sep 2011 Location: Germany Posts: 39 Rep Power: 14	However, you can set a Total Pressure and adjust the pressure level according to your required flow rate, right?

March 12, 2015, 00:16		#4
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Thanks PeMo. Can you explain a bit more please, how do I know the pressure level corresponding to my flow rate. Actually I was reading an article in which it was mentioned that in ANSYS Fluent volume flow rate and pressure both were applied as the inlet boundary condition. I wonder how it is possible to set two variables as inlet boundary condition either in Fluent or in CFX.

March 12, 2015, 03:53		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	It is numerically impossible to define both the pressure and velocity at a boundary in subsonic flow. You can do this in supersonic boundaries. If you have a steady state flow with an inlet and an outlet you simply apply the flow rate boundary to the inlet and the pressure boundary to the outlet or vice versa. Then you have specified the pressure and flow rate at a boundary - but the flow rate will only be as accurate as your imbalance convergence.

March 15, 2015, 17:19		#6
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Thanks Glenn. Actually I emailed the author of the article who claimed that he used both pressure and volume flow rate as inlet boundary condition. He says that in ANSYS Fluent 14.5 they are able to set these two variables (pressure and volume flow rate) as the inlet boundary condition. Does this make sense to you?

March 15, 2015, 17:21		#7
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	And also their flow is subsonic.