boundary condition with pressure AND mass flow rate

tsi07 · July 19, 2017, 14:45

Hi,

I am simulating the flow in a combustion chamber of an aircraft engine.
The pressure and the mass flow rate are well defined in the experimental data.
It is a compressible flow and the outlet is a pressure boundary condition at 1 atm.
For the numerical part, I want to define a boundary condition (BC) in fluent with a given mass flow rate and a given pressure.

In fluent, the "mass-flow-inlet" BC enables us to have a given mass flow rate but how can I define the pressure at the inlet?
There is an option to input an initial gauge pressure but I found in the help document this sentence in the "Mass flow inlet boundary conditions section": "The Supersonic/Initial Gauge Pressure is ignored by ANSYS Fluent whenever the flow is subsonic."
Hence I want to know is there a way to define the pressure at the inlet?

If not, how can I treat the problem?

LuckyTran · July 20, 2017, 09:39

You can't specify both pressure and mass flow at a boundary, that would over-constrain the problem.

granties360 · April 14, 2022, 09:03

Hi,

Have you found a way to solve this issue? I am experiencing a similar problem regarding the filling of a hydrogen tank.

Regards,
Ross

LuckyTran · April 14, 2022, 13:32

You can't specify both mass flow rate and pressure, it makes no physical sense, unless the flow is supersonic. If the flow is supersonic, then the option is readily available.

If your flow is not supersonic and you're trying to constrain both mass flow and pressure, then you need to rethink your approach because you're doing it wrong.

July 19, 2017, 14:45	boundary condition with pressure AND mass flow rate	#1
tsi07 Member Join Date: Mar 2012 Location: USA Posts: 33 Rep Power: 14	Hi, I am simulating the flow in a combustion chamber of an aircraft engine. The pressure and the mass flow rate are well defined in the experimental data. It is a compressible flow and the outlet is a pressure boundary condition at 1 atm. For the numerical part, I want to define a boundary condition (BC) in fluent with a given mass flow rate and a given pressure. In fluent, the "mass-flow-inlet" BC enables us to have a given mass flow rate but how can I define the pressure at the inlet? There is an option to input an initial gauge pressure but I found in the help document this sentence in the "Mass flow inlet boundary conditions section": "The Supersonic/Initial Gauge Pressure is ignored by ANSYS Fluent whenever the flow is subsonic." Hence I want to know is there a way to define the pressure at the inlet? If not, how can I treat the problem?

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July 20, 2017, 09:39		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	You can't specify both pressure and mass flow at a boundary, that would over-constrain the problem.

April 14, 2022, 09:03		#3
granties360 New Member Ross Grant Join Date: Apr 2022 Posts: 3 Rep Power: 4	Hi, Have you found a way to solve this issue? I am experiencing a similar problem regarding the filling of a hydrogen tank. Regards, Ross

April 14, 2022, 13:32		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	You can't specify both mass flow rate and pressure, it makes no physical sense, unless the flow is supersonic. If the flow is supersonic, then the option is readily available. If your flow is not supersonic and you're trying to constrain both mass flow and pressure, then you need to rethink your approach because you're doing it wrong.