CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

setting Timestep

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 27, 2013, 09:31
Exclamation setting Timestep
  #1
Member
 
Francesco
Join Date: Jan 2012
Posts: 31
Rep Power: 14
Cecco is on a distinguished road
Hi everybody,
I'm running a steady simulation of a centrifugal blower.
Usually I do the following:
1. I set a really small timestep order to E-06 with Upwind scheme;
2. after 1000 iterations I switch timestep to E-05 with upwind scheme;
3. when physical properties which I monitor are stable, I switch to Blend Factor =0.75 (so not completely High resolution) and wait for a new stable state.

This process usually works, but not now.
Until I use upwind solution seems reach the convergence, but when I switch to Blend factor 0.75 ( i tried 0.6 as well) it doesn't happen.
I changed a lot of timestep between E-5 and E-7, but seems no works.
Someone has an idea about this behaviour and about what I should do?

Thanks
Cecco is offline   Reply With Quote

Old   May 27, 2013, 19:50
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,665
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
This is typical behaviour when you switch to a more accurate discretisation scheme. It means your simulation is not very numerically stable. In your case this probably means you need better mesh quality.
ghorrocks is offline   Reply With Quote

Old   May 28, 2013, 04:08
Thumbs up
  #3
Member
 
Francesco
Join Date: Jan 2012
Posts: 31
Rep Power: 14
Cecco is on a distinguished road
I'll do a new mesh.
Thanks man. U precious!
Cecco is offline   Reply With Quote

Reply

Tags
cfx, convergence, convergence problem, timestep

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Residual level setting of Fluent lhlh ANSYS 2 November 17, 2012 22:35
Cells with t below lower limit Purushothama Siemens 2 May 31, 2010 22:58
LiftDrag utility from v12 to v141 cfdphil OpenFOAM Running, Solving & CFD 2 December 5, 2007 06:49
Ultra high temperature? bk Siemens 2 July 19, 2005 01:01
Warning 097- AB Siemens 6 November 15, 2004 05:41


All times are GMT -4. The time now is 08:46.