Boundary conditions while utilizing symmetry

ishan_ae · November 6, 2020, 02:11

I am trying to troubleshoot my setup for a subsonic compressible flow through a duct for some time now. The software is OpenFOAM but I have a general question about the boundary conditions I am using.

I have tried almost everything to troubleshoot my problems and BC is something I want to take a look at as a final step.

The experimental data consists of total pressure imposed at inlet and mass flow rate at the outlet.

If I have to utilize symmetry of the model should I divide by 2 the total pressure and mass flow rate values when I define my setup ?

flotus1 · November 6, 2020, 04:16

If you reduce the cross-section of your computational model, mass flow rate has to be adjusted accordingly. Otherwise, you would end up with different velocity than in the experimental setup.
Pressure on the other hand is an intensive quantity, and thus may not be changed.

ishan_ae · November 6, 2020, 04:22

Thank you for the information Alex. I was thinking on the same lines but wanted to get it confirmed.

November 6, 2020, 02:11	Boundary conditions while utilizing symmetry	#1
ishan_ae Member ishan Join Date: Oct 2017 Posts: 77 Rep Power: 8	I am trying to troubleshoot my setup for a subsonic compressible flow through a duct for some time now. The software is OpenFOAM but I have a general question about the boundary conditions I am using. I have tried almost everything to troubleshoot my problems and BC is something I want to take a look at as a final step. The experimental data consists of total pressure imposed at inlet and mass flow rate at the outlet. If I have to utilize symmetry of the model should I divide by 2 the total pressure and mass flow rate values when I define my setup ?

November 6, 2020, 04:16		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,400 Rep Power: 47	If you reduce the cross-section of your computational model, mass flow rate has to be adjusted accordingly. Otherwise, you would end up with different velocity than in the experimental setup. Pressure on the other hand is an intensive quantity, and thus may not be changed. ishan_ae likes this.

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November 6, 2020, 04:22		#3
ishan_ae Member ishan Join Date: Oct 2017 Posts: 77 Rep Power: 8	Thank you for the information Alex. I was thinking on the same lines but wanted to get it confirmed.