Questions about cfx

shanxuewenjdx · August 13, 2012, 21:48

Hi.
There is a question with the gear pump.
When the inlet was set as 0MPa, and massFlow at outlet(pressure was set 0MPa) was 2.4kg/s.
However, when the pressure at outlet was set 5Mpa,the massFlow at outlet was nearly 1.2kg/s.
So this is consistant with the real situation,or something is wrong with my setup.
I did this simulation with the method of Immersed Solid in CFX.
thanks!

ghorrocks · August 14, 2012, 08:00

I do not know what you are modelling in detail so cannot say for sure, but your results could be possible. You get 2.4 kg/s flow with no pressure gradient, and when the pump is pushing against a 5MPa pressure the flow rate slows to 1.2kg/s. With a positive displacement pump like this the loss in flow is presumably due to fluid leaking around the impeller.

shanxuewenjdx · August 14, 2012, 10:12

It is my model.

shanxuewenjdx · August 14, 2012, 10:20

At the very beginning, I thought it is the problem of leakage.But the radial gap, axial clearance and gear backlash were all set zero.When I set outlet 20MPa,the massflow at outlet was 0kg/s,also the pressure at inlet was 8MPa, while the toal pressure at inlet I set before was 0MPa.
So I can't figure out the problem . my model? mesh size?

ghorrocks · August 14, 2012, 19:17

Don't forget immersed solids work by using a scaling factor on a momentum source term. Flow will slowly filter through the solid region if that factor is not set high enough. Have you done a sensitivity analysis of the factor?

August 13, 2012, 21:48	Questions about cfx	#1
shanxuewenjdx Member Stefan Join Date: May 2012 Posts: 49 Rep Power: 13	Hi. There is a question with the gear pump. When the inlet was set as 0MPa, and massFlow at outlet(pressure was set 0MPa) was 2.4kg/s. However, when the pressure at outlet was set 5Mpa,the massFlow at outlet was nearly 1.2kg/s. So this is consistant with the real situation,or something is wrong with my setup. I did this simulation with the method of Immersed Solid in CFX. thanks!

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August 14, 2012, 08:00		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,697 Rep Power: 143	I do not know what you are modelling in detail so cannot say for sure, but your results could be possible. You get 2.4 kg/s flow with no pressure gradient, and when the pump is pushing against a 5MPa pressure the flow rate slows to 1.2kg/s. With a positive displacement pump like this the loss in flow is presumably due to fluid leaking around the impeller.

August 14, 2012, 10:20		#4
shanxuewenjdx Member Stefan Join Date: May 2012 Posts: 49 Rep Power: 13	At the very beginning, I thought it is the problem of leakage.But the radial gap, axial clearance and gear backlash were all set zero.When I set outlet 20MPa,the massflow at outlet was 0kg/s,also the pressure at inlet was 8MPa, while the toal pressure at inlet I set before was 0MPa. So I can't figure out the problem . my model? mesh size?

August 14, 2012, 19:17		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,697 Rep Power: 143	Don't forget immersed solids work by using a scaling factor on a momentum source term. Flow will slowly filter through the solid region if that factor is not set high enough. Have you done a sensitivity analysis of the factor?