CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CD-adapco

how to reduce correctors for transient flow

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 6, 2006, 22:50
Default how to reduce correctors for transient flow
  #1
Chinayu
Guest
 
Posts: n/a
Hi, everyone:

In a intake manifold, one pressure inlet, four pressure outlet, for each iteraction, the correctors are over 20, I have chang the pressure underrelaxtion factor,but it does not act active, I have checked the .info file, NSP is always over than 1000, how to solve the problem?

Thanks
  Reply With Quote

Old   May 8, 2006, 06:29
Default Re: how to reduce correctors for transient flow
  #2
John
Guest
 
Posts: n/a
In transient run, Uder-relaxation factors are not used. You can probably try to set under-relaxation factor for pressure correction by

NavCenter=>Analysis Controls=>Solution Controls=>Solution Method, in Solution setup, the 3rd item is URF, give a value of 0.7 or so.

  Reply With Quote

Old   May 8, 2006, 13:16
Default Re: how to reduce correctors for transient flow
  #3
vladimir
Guest
 
Posts: n/a
hi Chinayu,
the other way to get the pressure correctors below the limit of 20 is decrease the time step size. What is the value of courant number for your simulation?

  Reply With Quote

Old   May 8, 2006, 13:35
Default Re: how to reduce correctors for transient flow
  #4
Ben
Guest
 
Posts: n/a
To be honest it could be any number of things, although the obvious ones to look at are courant number, grid quality and turbulence model. Also look at boundary region suitability and ensure that you are not getting any whacky gradients from poor simulation setup. Which equations are not converging and are you getting any other warnings?

  Reply With Quote

Old   May 9, 2006, 01:15
Default Re: how to reduce correctors for transient flow
  #5
anand
Guest
 
Posts: n/a
hi chinayu

in the command window

type RELAX and enter

it will ask for which parameter to be changed .....

example

RELAX 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 it will change all param to 0.5

i hope you got required solution ..wish u all the best

anand

  Reply With Quote

Old   May 9, 2006, 08:25
Default Re: how to reduce correctors for transient flow
  #6
vladimir
Guest
 
Posts: n/a
hi anand,
as john mentioned, you cannot do any kind of relaxation that is based on transfer of information from previous to the actual solution step, which is the case you suggested. You would change the physics of your problem in this way. Look at any CFD book (e.g. Malalasekera). The only way you can relax with transient starCD simulation and PISO is decrease time step size, or change the relaxation for pressure correction, relates to the PISO algorithm, or just go out to a pub.
  Reply With Quote

Old   May 10, 2006, 09:02
Default Re: how to reduce correctors for transient flow
  #7
chinayu
Guest
 
Posts: n/a
I have decreased time step to 0.1CA and the courant number is far below 1, so I think the time step is short enough. I have also checked the mesh quality, the mesh quality is not bad, but the presssure boundary are changed, I get the boundary pressure from GT-Power.
  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
Transient Flow, Transient Pressure in Work Bench Erich CFX 1 May 8, 2007 11:55
When and how to apply nonOrthogonal correctors vvqf OpenFOAM Running, Solving & CFD 1 March 22, 2006 05:21
how to reduce y+ Cindy Jones FLUENT 2 January 17, 2003 22:12
Transient flow omondi CFX 8 November 8, 2001 01:47
how can I reduce the file size of transient data Yuan-Heng Huang CD-adapco 3 December 1, 2000 22:16


All times are GMT -4. The time now is 19:02.