Rotating wall - with steady or transient?

Roland R · March 4, 2016, 10:36

Hello All,

I detected an interesting problem. I am calculating a clutch with opened discs. The walls of rotational disc are defined as rotating wall while the stationary discs are calculated as stationary walls. Based on my expactation, the pressure decreases in the thin gap caused by rotation walls as a result, this region will have a suction effect on the oil.

1. I tried to complate the model in steady state but the suction effect did not occure. Moreover, the thin gap (between the rot/stat walls) generated a high choking effect for the oil.

2. I tried to complate it in transient. The result is total different and real. To tell the truth, I am surprised...

My main problem is that the presently model is a test case with low element number. I should use this method for a complicated clutch geometry including about 13-15 million elements which will result extreme high calculation time.

Do you have any ideas to solve this problem in steady?

Thanks a lot;
Roland

ghorrocks · March 5, 2016, 04:48

If you are getting a different result when you run it transient to steady then that suggests the flow is transient so a steady state run is not appropriate.

It also sounds like you have not done a mesh refinement study yet, so anything could happen as you refine the mesh. So you will need to refine the mesh until you are getting realistic results before you make any conclusions about steady versus transient.

March 4, 2016, 10:36	Rotating wall - with steady or transient?	#1
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	Hello All, I detected an interesting problem. I am calculating a clutch with opened discs. The walls of rotational disc are defined as rotating wall while the stationary discs are calculated as stationary walls. Based on my expactation, the pressure decreases in the thin gap caused by rotation walls as a result, this region will have a suction effect on the oil. 1. I tried to complate the model in steady state but the suction effect did not occure. Moreover, the thin gap (between the rot/stat walls) generated a high choking effect for the oil. 2. I tried to complate it in transient. The result is total different and real. To tell the truth, I am surprised... My main problem is that the presently model is a test case with low element number. I should use this method for a complicated clutch geometry including about 13-15 million elements which will result extreme high calculation time. Do you have any ideas to solve this problem in steady? Thanks a lot; Roland

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March 5, 2016, 04:48		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,816 Rep Power: 144	If you are getting a different result when you run it transient to steady then that suggests the flow is transient so a steady state run is not appropriate. It also sounds like you have not done a mesh refinement study yet, so anything could happen as you refine the mesh. So you will need to refine the mesh until you are getting realistic results before you make any conclusions about steady versus transient.