help ! centrifugal compressor stimulation

Aysiyi · October 12, 2013, 22:14

Hello,

I'm new to CFX software. I am trying to stimulate a centrifugal compressor. the model include a impeller passage, a diffuser passage,a whole volute. The inlet boundry is total pressure, total temperature, direction of velocity. The outlet boundry is mass flow. it is a steady stimulation. But after 1200 iterations, the mass flow of inlet and outlet isn't equal. If I only compute the impeller and diffuser, it can be converged, and If I only compute the volute, it also can be converged. So I think the problem is the condition of outlet can't be propagated to the inlet. Maybe the problem is the interface of diffuser outlet and volute inlet, Who can help me? thanks!

ghorrocks · October 13, 2013, 02:23

There is many things which could cause this. Inadequate convergence and choked flow are two which come to mind.

Aysiyi · October 13, 2013, 07:19

Quote:

Originally Posted by ghorrocks

There is many things which could cause this. Inadequate convergence and choked flow are two which come to mind.

what's inadequate convergence? is it right convergence or wrong?

ghorrocks · October 13, 2013, 07:44

I recommend you read the section in the documentation "Obtaining Convergence".

Aysiyi · October 13, 2013, 11:11

ok! thanks

Aysiyi · October 14, 2013, 03:11

Quote:

Originally Posted by ghorrocks

I recommend you read the section in the documentation "Obtaining Convergence".

I have read the documentation "Obtaining Convergence". But I havn't found some useful information,. Can you give me some help? Can you interprete the "Inadequate convergence " for me? Thank you very much!

ghorrocks · October 14, 2013, 06:42

This is basic CFD and you are not going to be able to get far without knowing what it means. You really need to get a CFD textbook and read about the basic concepts.

CFD software uses iterative methods to converge to a solution. One of the measures of the accuracy of that solution is the residual. The smaller the residual, the smaller the error. But to understand what it really means you need to read a CFD textbook.

October 12, 2013, 22:14	help ! centrifugal compressor stimulation	#1
Aysiyi Member aysiyi Join Date: Nov 2012 Posts: 40 Rep Power: 14	Hello, I'm new to CFX software. I am trying to stimulate a centrifugal compressor. the model include a impeller passage, a diffuser passage,a whole volute. The inlet boundry is total pressure, total temperature, direction of velocity. The outlet boundry is mass flow. it is a steady stimulation. But after 1200 iterations, the mass flow of inlet and outlet isn't equal. If I only compute the impeller and diffuser, it can be converged, and If I only compute the volute, it also can be converged. So I think the problem is the condition of outlet can't be propagated to the inlet. Maybe the problem is the interface of diffuser outlet and volute inlet, Who can help me? thanks!

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October 13, 2013, 02:23		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	There is many things which could cause this. Inadequate convergence and choked flow are two which come to mind.

October 13, 2013, 07:44		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	I recommend you read the section in the documentation "Obtaining Convergence".

October 13, 2013, 11:11		#5
Aysiyi Member aysiyi Join Date: Nov 2012 Posts: 40 Rep Power: 14	ok! thanks

October 14, 2013, 06:42		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	This is basic CFD and you are not going to be able to get far without knowing what it means. You really need to get a CFD textbook and read about the basic concepts. CFD software uses iterative methods to converge to a solution. One of the measures of the accuracy of that solution is the residual. The smaller the residual, the smaller the error. But to understand what it really means you need to read a CFD textbook.