rotational domain vs stationary domain

payan · March 21, 2019, 22:56

hey guys, i'm using CFX simulating the flow through a hollow tube. The boundary conditions are total pressure and total temperature at the inlet and static pressure at the outlet. And inner surface rotates at 7000 r/min while the outer surface surface is stationary.

I tried two methods to solve this question:
1) the tube has a stationary frame type. Inner surface wall velocity is 7000 r/min. outer surface is still.
2) the tube has a rotational frame type. inner surface is still relative to rotational frame. outer surface wall velocity is counter rotating.
other boundary conditions are all the same.

the pressure on the inner surface using the first method appears a little larger than that using the second method according to the results. is it normal? what is the difference between this two methods?

Hope some can help me. Sincerely

ghorrocks · March 21, 2019, 23:23

If the simulations are properly converged and validated they should give the same result. So you should check time step, mesh and convergence sensitivity before making conclusions about the results.

Opaque · March 22, 2019, 13:51

Have you selected the alternate rotation model?

payan · March 25, 2019, 22:10

thanks for reply, i'm new to cfx. what is alternate rotation model?

according to my simulation, the convergence of second method is rather poor. so i'm gonna use the first one.

ghorrocks · March 25, 2019, 22:13

From what you describe it would be expected that convergence in a rotational frame would be harder. Opaque's suggestion to use the alternate rotation model may have partly offset that. If you want to learn about the model (or any other CFX model) look in the CFX documentation.

March 21, 2019, 22:56	rotational domain vs stationary domain	#1
payan New Member Yang Pan Join Date: Jun 2015 Posts: 4 Rep Power: 11	hey guys, i'm using CFX simulating the flow through a hollow tube. The boundary conditions are total pressure and total temperature at the inlet and static pressure at the outlet. And inner surface rotates at 7000 r/min while the outer surface surface is stationary. I tried two methods to solve this question: 1) the tube has a stationary frame type. Inner surface wall velocity is 7000 r/min. outer surface is still. 2) the tube has a rotational frame type. inner surface is still relative to rotational frame. outer surface wall velocity is counter rotating. other boundary conditions are all the same. the pressure on the inner surface using the first method appears a little larger than that using the second method according to the results. is it normal? what is the difference between this two methods? Hope some can help me. Sincerely

March 21, 2019, 23:23		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	If the simulations are properly converged and validated they should give the same result. So you should check time step, mesh and convergence sensitivity before making conclusions about the results. payan likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 25, 2019, 22:13		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	From what you describe it would be expected that convergence in a rotational frame would be harder. Opaque's suggestion to use the alternate rotation model may have partly offset that. If you want to learn about the model (or any other CFX model) look in the CFX documentation. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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March 22, 2019, 13:51		#3
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	Have you selected the alternate rotation model?

March 25, 2019, 22:10		#4
payan New Member Yang Pan Join Date: Jun 2015 Posts: 4 Rep Power: 11	thanks for reply, i'm new to cfx. what is alternate rotation model? according to my simulation, the convergence of second method is rather poor. so i'm gonna use the first one.