(OpenFoam) outlet velocity boundary condition depending on outlet pressure (PUMP)

giordy · March 27, 2019, 03:23

Hi All,

I would like to simulate how a pump work when it suck air from a vessel. In particular I am interested in the boundary condition at outlet of the vessel where the air is sucked with a velocity that depends on the pressure at outlet. Is there any boundary condition in OpenFoam that I can use for it?
Thanks.

regards,
Stefano

LuckyTran · March 28, 2019, 06:23

fanPressure?

Tobi · March 28, 2019, 06:28

Quote:

Originally Posted by LuckyTran

fanPressure?

This will not work, as you need two patches where you apply a pressure drop. If you know the pressure at the inlet of the pump, then you can build a pressure based boundary condition couple. At the inlet you define a totalPressure and at the outlet a fixedValue. The velocity should be pressureInletVelocity and zeroGradient respectively.

giordy · March 28, 2019, 07:07

Hi Tobias,

I only have a patch that is the exit of the vessel. At this exit I would like to apply the velocity (or flowrate) condition based on the pressure at the exit itself (or in the vessel).

Tobi · March 28, 2019, 07:14

Hi Stefano,

you have two options:

Flow Rate / Velocity based fluid motion (in simple words: you get the information of a pressure gradient)
Pressure based fluid motion (in simple words: you get the information of the mass flow rate)

If you know the mass flow rate, you can apply the mass flow rate at the outlet (where is the problem?). Accordingly, you use a zero pressure gradient there and a fixed on at the inlet/or a totalPressure depending on your needs and set-up.

giordy · March 28, 2019, 07:21

Hi Tobias,

This is a transient case. My flowrate / velocity should change depending on which is the pressure in the vessel.

Tobi · March 29, 2019, 07:48

Hi,

so then you should have a pressure based force. Where is the problem?

giordy · March 29, 2019, 07:55

Hi Tobias,

How would you write such a BC for velocity and pressure?

March 27, 2019, 03:23	(OpenFoam) outlet velocity boundary condition depending on outlet pressure (PUMP)	#1
giordy New Member stefano zinna Join Date: Mar 2009 Posts: 29 Rep Power: 17	Hi All, I would like to simulate how a pump work when it suck air from a vessel. In particular I am interested in the boundary condition at outlet of the vessel where the air is sucked with a velocity that depends on the pressure at outlet. Is there any boundary condition in OpenFoam that I can use for it? Thanks. regards, Stefano

March 28, 2019, 07:14		#5
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	Hi Stefano, you have two options: Flow Rate / Velocity based fluid motion (in simple words: you get the information of a pressure gradient) Pressure based fluid motion (in simple words: you get the information of the mass flow rate) If you know the mass flow rate, you can apply the mass flow rate at the outlet (where is the problem?). Accordingly, you use a zero pressure gradient there and a fixed on at the inlet/or a totalPressure depending on your needs and set-up. __________________ Keep foaming, Tobias Holzmann

March 29, 2019, 07:48		#7
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	Hi, so then you should have a pressure based force. Where is the problem? __________________ Keep foaming, Tobias Holzmann

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March 28, 2019, 06:23		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,673 Rep Power: 65	fanPressure?

March 28, 2019, 07:07		#4
giordy New Member stefano zinna Join Date: Mar 2009 Posts: 29 Rep Power: 17	Hi Tobias, I only have a patch that is the exit of the vessel. At this exit I would like to apply the velocity (or flowrate) condition based on the pressure at the exit itself (or in the vessel).

March 28, 2019, 07:21		#6
giordy New Member stefano zinna Join Date: Mar 2009 Posts: 29 Rep Power: 17	Hi Tobias, This is a transient case. My flowrate / velocity should change depending on which is the pressure in the vessel.

March 29, 2019, 07:55		#8
giordy New Member stefano zinna Join Date: Mar 2009 Posts: 29 Rep Power: 17	Hi Tobias, How would you write such a BC for velocity and pressure?