Pressure outlet boundary condition

Miguel Parente · November 6, 2017, 14:39

Hi everyone! I was conducting a combustion simulation with ppdf model, where I have several pressure outlet boundary conditions, where they are actually inlet conditions. My doubt is in the Mixture Fraction Profile of the pressure outlet do I have to put [0,1] to indicate that is air(oxidizer) that is entering? Or by default is oxidizer?

The point is I have monitoring the mass fraction at that specific boundary, and it is correct, however, when I put [0,1] it is still correct, but sometimes I star to have a combustion process in the boundary when it is far away from the burner, and no fuel is present there.

Thanks all

me3840 · November 10, 2017, 01:42

The default may differ depending on the number of species. You must enter in a correct mixture fraction, yes.

I would not advise using the pressure outlet as an inlet. Stagnation inlet is better formulated for this.

If you are having combusion happen where it's physically impossible this suggests your simulation is not converging or has other problems.

Miguel Parente · November 10, 2017, 10:56

Dear me3840, thanks a lot for your time. Yes I understand that I don't have convergence. In fact when i say that the only entrance is air, I have a non physical solution, in the control volume I have a considerable number of cells in the sum of mass fraction is well below 1. I will follow your advise and see if Stagnation inlet works better in my case. Thanks a lot for the help

November 6, 2017, 14:39	Pressure outlet boundary condition	#1
Miguel Parente New Member Miguel Join Date: May 2017 Posts: 10 Rep Power: 9	Hi everyone! I was conducting a combustion simulation with ppdf model, where I have several pressure outlet boundary conditions, where they are actually inlet conditions. My doubt is in the Mixture Fraction Profile of the pressure outlet do I have to put [0,1] to indicate that is air(oxidizer) that is entering? Or by default is oxidizer? The point is I have monitoring the mass fraction at that specific boundary, and it is correct, however, when I put [0,1] it is still correct, but sometimes I star to have a combustion process in the boundary when it is far away from the burner, and no fuel is present there. Thanks all

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November 10, 2017, 01:42		#2
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	The default may differ depending on the number of species. You must enter in a correct mixture fraction, yes. I would not advise using the pressure outlet as an inlet. Stagnation inlet is better formulated for this. If you are having combusion happen where it's physically impossible this suggests your simulation is not converging or has other problems.

November 10, 2017, 10:56		#3
Miguel Parente New Member Miguel Join Date: May 2017 Posts: 10 Rep Power: 9	Dear me3840, thanks a lot for your time. Yes I understand that I don't have convergence. In fact when i say that the only entrance is air, I have a non physical solution, in the control volume I have a considerable number of cells in the sum of mass fraction is well below 1. I will follow your advise and see if Stagnation inlet works better in my case. Thanks a lot for the help