Inlet, no Outlet

Torque_Converter · March 30, 2012, 14:35

Hello All,

I am looking to see the time it takes, and the pressure created when a flow of oil is introduced to a previously air filled chamber. I am well versed in inlet/outlet flow and rotational closed domain flow, but this one stumps me.

Thanks

ghorrocks · March 31, 2012, 07:17

Can you describe it a bit more completely? Do you have a chamber filled with air at time zero, and then you add some oil to it (how? under pressure or a defined flow rate?) and the pressure in the air chamber increases? Does the chamber have any inlets or outlets? Is it steady state or transient?

Torque_Converter · March 31, 2012, 09:28

Yes, a chamber is filled with air at t=0s. This chamber has no outlet, only an inlet. At t=0s oil is introduced through this inlet at P=2 atm (just random numbers), consistently applied. The air would be displaced, and some diffusion into the oil but i'm not worried about that so much. I suppose it could be modeled as an empty chamber at t=0s and then oil added and it would still be accurate.
While the boundary conditions are steady state, I would say the problem is a transient one. The goal of the analysis is to determine how long this is taking since the fluid is VERY viscous and the inlet is rather small.

ghorrocks · March 31, 2012, 16:18

This sounds like something which can be worked out with elementary thermodynamics as a pen and paper calculation, not needing CFD at all. Why are you thinking of doing it using CFD?

Torque_Converter · March 31, 2012, 16:28

I would agree to be honest, pressure drop, mass flow rate, etc. all easy enough to look into. But I am often asked to do things which produce "pretty pictures". Honestly, I may do the hand calculations and then force a simulation to match. But ultimately, yes, knowing the entry conditions, fluid properties, etc. it is an extremely elementary problem.

ghorrocks · April 1, 2012, 06:48

The simulation you describe appears to be a straight forward transient compressible gas/oil free surface simulation. But to get a mesh fine enough to look "pretty" will require a fine mesh, and that means a long run time. So this model is going to take a while to develop and a while to run. If all you want is pretty pictures then I recommend photoshop

March 30, 2012, 14:35	Inlet, no Outlet	#1
Torque_Converter Member Join Date: Jan 2012 Location: Indiana, USA Posts: 68 Rep Power: 3	Hello All, I am looking to see the time it takes, and the pressure created when a flow of oil is introduced to a previously air filled chamber. I am well versed in inlet/outlet flow and rotational closed domain flow, but this one stumps me. Thanks

March 31, 2012, 07:17		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 7,026 Rep Power: 60	Can you describe it a bit more completely? Do you have a chamber filled with air at time zero, and then you add some oil to it (how? under pressure or a defined flow rate?) and the pressure in the air chamber increases? Does the chamber have any inlets or outlets? Is it steady state or transient? Torque_Converter likes this.

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March 31, 2012, 09:28		#3
Torque_Converter Member Join Date: Jan 2012 Location: Indiana, USA Posts: 68 Rep Power: 3	Yes, a chamber is filled with air at t=0s. This chamber has no outlet, only an inlet. At t=0s oil is introduced through this inlet at P=2 atm (just random numbers), consistently applied. The air would be displaced, and some diffusion into the oil but i'm not worried about that so much. I suppose it could be modeled as an empty chamber at t=0s and then oil added and it would still be accurate. While the boundary conditions are steady state, I would say the problem is a transient one. The goal of the analysis is to determine how long this is taking since the fluid is VERY viscous and the inlet is rather small.

March 31, 2012, 16:18		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 7,026 Rep Power: 60	This sounds like something which can be worked out with elementary thermodynamics as a pen and paper calculation, not needing CFD at all. Why are you thinking of doing it using CFD?

March 31, 2012, 16:28		#5
Torque_Converter Member Join Date: Jan 2012 Location: Indiana, USA Posts: 68 Rep Power: 3	I would agree to be honest, pressure drop, mass flow rate, etc. all easy enough to look into. But I am often asked to do things which produce "pretty pictures". Honestly, I may do the hand calculations and then force a simulation to match. But ultimately, yes, knowing the entry conditions, fluid properties, etc. it is an extremely elementary problem.

April 1, 2012, 06:48		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 7,026 Rep Power: 60	The simulation you describe appears to be a straight forward transient compressible gas/oil free surface simulation. But to get a mesh fine enough to look "pretty" will require a fine mesh, and that means a long run time. So this model is going to take a while to develop and a while to run. If all you want is pretty pictures then I recommend photoshop