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

residuals of bin fraction remains constant

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 10, 2020, 11:26
Default residuals of bin fraction remains constant
  #1
Member
 
mln
Join Date: Dec 2019
Posts: 36
Rep Power: 2
melj is on a distinguished road
Hello

I am modeling a multiphase bubble column using Euler-Euler; RSM for turbulence; and PBM. The residuals of bin-fraction appear to be constant after around 30 iterations. Why does this happen? Does this mean that I could run the simulations with lesser no. of iterations per time step? I am using 350 iterations/time step currently.

thank you
melj is offline   Reply With Quote

Old   March 11, 2020, 03:17
Default Residual and Convergence
  #2
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 1,305
Blog Entries: 1
Rep Power: 21
vinerm is on a distinguished road
Are the residuals low enough? If yes, then it is good.

The idea behind number of iterations per time-step and the size of time-step is to ensure such a value of time-step so that no more than 30 iterations are required for convergence in each time-step. So, 350 iterations is really too high a value. In case the simulation takes more than 30 iterations to converge, reduce the time-step. So, in your case, it is good that it is converging within 30 iterations.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared on the Forum
vinerm is offline   Reply With Quote

Old   March 12, 2020, 15:39
Default
  #3
Member
 
mln
Join Date: Dec 2019
Posts: 36
Rep Power: 2
melj is on a distinguished road
I wanted to get the bin fraction residuals below 10^-3. But, it does not go below that and so it does not converge. The value of residual reduces to a constant. I feel that its pointless to let it run for 350 iterations and so rather run it for 50 iterations for every time step.

Or would you suggest to work with the URF?
melj is offline   Reply With Quote

Old   March 13, 2020, 04:27
Default Residuals
  #4
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 1,305
Blog Entries: 1
Rep Power: 21
vinerm is on a distinguished road
Computers are dumb, so, they can only consider it 1e-3 if it really is 1e-3. But we can observe it better. So, if it is close to 1e-3, such as 2e-3 or even 3e-3, it is alright. However, if it is at least an order larger, then you can play with URFs as well as gradient limiters. Residuals gets stalled with standard limiters. You can try using cell-to-cell limiters and see if that improves the residuals.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared on the Forum
vinerm is offline   Reply With Quote

Old   March 13, 2020, 17:06
Default
  #5
Member
 
mln
Join Date: Dec 2019
Posts: 36
Rep Power: 2
melj is on a distinguished road
thank you vinerm.
melj is offline   Reply With Quote

Reply

Tags
bin fractions, residuals

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
decomposePar problem: Cell 0contains face labels out of range vaina74 OpenFOAM Pre-Processing 32 February 7, 2018 08:26
Constant Initial Residuals and divergence Gubevens OpenFOAM Running, Solving & CFD 0 May 24, 2016 05:44
multiphaseEulerFoam (OF2.3.0) : Courant number explodes when running in parallel Mehrez OpenFOAM Running, Solving & CFD 10 May 18, 2016 11:44
Solution not converging, but oscillating residuals around a constant value Irene FLUENT 2 February 7, 2012 11:55
Two-Phase Buoyant Flow Issue Miguel Baritto CFX 4 August 31, 2006 12:02


All times are GMT -4. The time now is 00:54.