# divergence transient study

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

 March 19, 2012, 16:49 divergence transient study #1 Member   andres Join Date: Sep 2010 Posts: 44 Rep Power: 9 Hi folks I am performing a transient study and after 3000 iterations it takes place a divergence of residuals and so my results... Is is: Density-based Energy On Laminar Flow Courant Number 0.1 (which works perfect) Implicit Second Order Transient condicionts: Time Step Size = 0.1 seg Number Steps = 5000 Max Iter/ Time Step = 50 Everything runs well and behaves as supposed but when it reaches 3000 iterations....diverges! Any advice?? is there anything else I can do?? Any suggestion?? Thanks in advance Regards

March 22, 2012, 14:05
#2
Member

banty
Join Date: Mar 2012
Posts: 52
Rep Power: 7
Quote:
 Originally Posted by cfdhydraulic Hi folks I am performing a transient study and after 3000 iterations it takes place a divergence of residuals and so my results... Is is: Density-based Energy On Laminar Flow Courant Number 0.1 (which works perfect) Implicit Second Order Transient condicionts: Time Step Size = 0.1 seg Number Steps = 5000 Max Iter/ Time Step = 50 Everything runs well and behaves as supposed but when it reaches 3000 iterations....diverges! Any advice?? is there anything else I can do?? Any suggestion?? Thanks in advance Regards
Hello,

Plz Increase the maximum coarse level under multigrid panel (Advanced solution control)
and lets see its works or not.

 March 22, 2012, 14:07 #3 Member   andres Join Date: Sep 2010 Posts: 44 Rep Power: 9 I will do it, thanks

 March 22, 2012, 17:21 #4 Member   andres Join Date: Sep 2010 Posts: 44 Rep Power: 9 I set even 10000 in max coarse and it didn't change at all the results...

 March 23, 2012, 13:36 #5 Member   banty Join Date: Mar 2012 Posts: 52 Rep Power: 7 no, even 10 is sufficient. 10000 is not correct(unreal). u can play with multigrid option. (pre sweeps, post sweeps) . hopefully it will help. http://https://www.sharcnet.ca/Software/Fluent12/html/ug/node794.htm r u using explicit method to time advancement? ( u set courant no 0.1.) try using implicit method and please post whether it is working or not.

 March 23, 2012, 13:47 #6 Member   andres Join Date: Sep 2010 Posts: 44 Rep Power: 9 yes I am using implicit method (itīs default) , and it gives me the possibility to set courant number. I have tried from 0.1 to 5 (0.1 more precise but slower and 5 very coarse) max coarse number didnīt affect my calculations nor residuals. I am going to surf this site and Iīll let you know! Thank you!

 March 23, 2012, 14:12 #7 Member   banty Join Date: Mar 2012 Posts: 52 Rep Power: 7 Hello cfdhydraulic, Plase don't make different thread for same problem as i think u have two or three threads for this problem. its confusing, right!!.

 March 23, 2012, 14:16 #8 Member   andres Join Date: Sep 2010 Posts: 44 Rep Power: 9 yeah sorry some times I get confused with this forum... sorry about that! no happens again

 March 23, 2012, 14:38 #9 New Member   Nik Join Date: Mar 2010 Location: Michigan Posts: 25 Rep Power: 9 Try reducing the time step size and simultaneous reduce the URF Nik

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post jlefevre76 FLUENT 2 February 5, 2013 10:53 akj Main CFD Forum 0 February 1, 2012 08:53 SamCanuck FLUENT 2 August 31, 2011 11:34 siw CFX 5 October 30, 2010 05:45 john Siemens 1 November 26, 2005 02:15

All times are GMT -4. The time now is 18:54.