high pressure boundary condition

fragzilla · September 10, 2012, 15:25

Hello, im currently working on simulating some channels in an hydralic pump, but I got some problems with the boundary conditions due the high pressure.

The problem consist of a 90 degree bending pipe, I've been trying to use a normal velocity around 20m/s for the inlet boundary condition and for the outlet i've been trying diffrent kind of pressure conditions, with 'relative pressure' equal set to 220 bar. The domains referense pressure is set to 1 atm.
the reasons of my problem could be that I use the standard water model instead of oil?
and another strange thing is that the models works fine every time i run it with relative pressure equal to 0...

The thing im investigating is the pressure loss in the channel for a flow of 20m/s and a exiting pressure of 220bar

ghorrocks · September 10, 2012, 19:27

Is the fluid incompressible? Is the exit boundary pressure the only place pressure is set at?

fragzilla · September 13, 2012, 16:38

I want the outlet to have the pressure of 220 Bar, its supposed to be hydralic oil,

I solved the problem with outlet and average static pressure, and did use upwind and then high resolution and got a solution

Thanks anyways ghorrocks

ghorrocks · September 13, 2012, 20:22

You have not answered my questions. Is the flow incompressible? Is the exit the only place the pressure is set at?

If this is the only place the pressure is set then you would be better off to use a boundary condition pressure of 0 bar, and a reference pressure of 220bar. This will reduce round off errors.

fragzilla · September 14, 2012, 02:13

yes, the flow is assumed to be incompressible and i've only used pressure boundary conditions at the end. the case i basicly to what the pressure need to be in start to get 220bar out,

ghorrocks · September 14, 2012, 03:40

In that case set the reference pressure to 220 bar and the outlet pressure to 0 bar. This will reduce round off errors and make convergence easier.

September 10, 2012, 15:25	high pressure boundary condition	#1
fragzilla New Member Join Date: Apr 2012 Posts: 3 Rep Power: 14	Hello, im currently working on simulating some channels in an hydralic pump, but I got some problems with the boundary conditions due the high pressure. The problem consist of a 90 degree bending pipe, I've been trying to use a normal velocity around 20m/s for the inlet boundary condition and for the outlet i've been trying diffrent kind of pressure conditions, with 'relative pressure' equal set to 220 bar. The domains referense pressure is set to 1 atm. the reasons of my problem could be that I use the standard water model instead of oil? and another strange thing is that the models works fine every time i run it with relative pressure equal to 0... The thing im investigating is the pressure loss in the channel for a flow of 20m/s and a exiting pressure of 220bar

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September 10, 2012, 19:27		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Is the fluid incompressible? Is the exit boundary pressure the only place pressure is set at?

September 13, 2012, 16:38		#3
fragzilla New Member Join Date: Apr 2012 Posts: 3 Rep Power: 14	I want the outlet to have the pressure of 220 Bar, its supposed to be hydralic oil, I solved the problem with outlet and average static pressure, and did use upwind and then high resolution and got a solution Thanks anyways ghorrocks

September 13, 2012, 20:22		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	You have not answered my questions. Is the flow incompressible? Is the exit the only place the pressure is set at? If this is the only place the pressure is set then you would be better off to use a boundary condition pressure of 0 bar, and a reference pressure of 220bar. This will reduce round off errors.

September 14, 2012, 02:13		#5
fragzilla New Member Join Date: Apr 2012 Posts: 3 Rep Power: 14	yes, the flow is assumed to be incompressible and i've only used pressure boundary conditions at the end. the case i basicly to what the pressure need to be in start to get 220bar out,

September 14, 2012, 03:40		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	In that case set the reference pressure to 220 bar and the outlet pressure to 0 bar. This will reduce round off errors and make convergence easier.