CFD Online URL
[Sponsors]
Home > Forums > CFX

About convergence

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   May 31, 2005, 00:29
Default About convergence
  #1
LQ
Guest
 
Posts: n/a
I am using CFX to solve a governning stage of a steam turbine which have three domains : the strengthening ring,stator and rotor.

I solved the flow field of the stator first,then added the rotor, finally solved all the three components as a whole stage.

During the procedure,I found that the more domains there were, the longer time will elapse for the caculation to converge.

Is there anybody else has this experience and know the reason?
  Reply With Quote

Old   May 31, 2005, 00:35
Default Re: About convergence
  #2
LQ
Guest
 
Posts: n/a
I mean "the longer time" to the iteration steps.
  Reply With Quote

Old   May 31, 2005, 19:34
Default Re: About convergence
  #3
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

I assume you mean a longer total physical timestep to converge. I can see this being caused by two factors, firstly adding extra bits to the model puts longer timescale effects into the model (that is flow interaction between blade rows); and secondly the rows are probably connected with GGI interfaces and they will require a little extra time to converge.

Regards, Glenn Horrocks
  Reply With Quote

Old   June 3, 2005, 00:43
Default Re: About convergence
  #4
Robin
Guest
 
Posts: n/a
By "longer time", do you mean wall clock time? I.e. it took more time to run? If so, the answer is simple: you are solving a bigger problem.

The solver run time scales linearly with with number of equations and the number of nodes. Double the nodes, it takes twice as long. Similarly, if you add equations to solve (such as heat transfer, or an additional variable), it takes proportionally longer for each timestep. This does not necessarily mean it requires more iterations. Each run make take 100 iterations, but each iteration get's a bit longer.

Regards, Robin
  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Convergence Centurion2011 FLUENT 21 November 18, 2014 05:17
problem with Min/max rho tH3f0rC3 OpenFOAM 7 February 23, 2013 06:37
Force can not converge colopolo CFX 13 October 4, 2011 23:03
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 02:17
Defect correction and convergence ganesh Main CFD Forum 4 June 30, 2006 15:20


All times are GMT -4. The time now is 03:20.