Outlet boundry condition

mani4039 · October 13, 2020, 16:03

Hi,
I have a valve and I am working on a pressure drop simulation.
I have the value for the mass flow rate at the inlet and the outlet will open at a reservoir pressure of 100 bars. What pressure should I specify at the outlet of the valve ?
Thanks for any input!

evcelica · October 13, 2020, 16:39

Usually make reference pressure 100 bar, then set outlet to 0.

mani4039 · October 13, 2020, 17:09

Thanks!
I am expecting cavitation and trying to introduce the back pressure to reduce it but not sure how to introduce the back pressure at the outlet boundary condition.
If I set 100 bar reference and Poutlet to 0 bar, would it equate to a back pressure of 100 Bars at the outlet ?

evcelica · October 14, 2020, 13:58

Yes, Outlet Pressure will actually say "relative" pressure, as it is relative to the reference pressure.

You could also set reference pressure to 0, and outlet relative pressure to 100 bar, but this will have more truncation error in the numerical solver.

October 13, 2020, 16:03	Outlet boundry condition	#1
mani4039 New Member Choose One... Join Date: Oct 2020 Posts: 5 Rep Power: 5	Hi, I have a valve and I am working on a pressure drop simulation. I have the value for the mass flow rate at the inlet and the outlet will open at a reservoir pressure of 100 bars. What pressure should I specify at the outlet of the valve ? Thanks for any input!

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October 13, 2020, 16:39		#2
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,167 Rep Power: 23	Usually make reference pressure 100 bar, then set outlet to 0.

October 13, 2020, 17:09		#3
mani4039 New Member Choose One... Join Date: Oct 2020 Posts: 5 Rep Power: 5	Thanks! I am expecting cavitation and trying to introduce the back pressure to reduce it but not sure how to introduce the back pressure at the outlet boundary condition. If I set 100 bar reference and Poutlet to 0 bar, would it equate to a back pressure of 100 Bars at the outlet ?

October 14, 2020, 13:58		#4
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,167 Rep Power: 23	Yes, Outlet Pressure will actually say "relative" pressure, as it is relative to the reference pressure. You could also set reference pressure to 0, and outlet relative pressure to 100 bar, but this will have more truncation error in the numerical solver.