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

Newton Solver failure with particle breakup at walls

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 30, 2015, 11:50
Default Newton Solver failure with particle breakup at walls
  #1
cvh
New Member
 
Chait
Join Date: Apr 2014
Posts: 14
Rep Power: 12
cvh is on a distinguished road
Hello all;

I am trying to implement particle breakup due to impingement on walls. I have been trying to use the pt_breakup_wall example user routine that is provided in the examples of user fortran in CFX installation directory. But with particle breakup, the Newton solver seems to fail while calculating total pressure. The continuous phase is modeled using the built-in Peng-Robinson equation of state.

I have tried increasing the number of iterations in the Newton Solver, as well as decreasing the under-relaxation factors, without any success.

I have also tried running the case on a finer grid with smaller time-steps. Also, the simulation runs fine when the breakup factor is kept at 1.

Has anyone encountered this type of problem before? If so, I'd appreciate any tips/suggestions.

Thanks!
cvh
cvh is offline   Reply With Quote

Old   March 30, 2015, 18:40
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,871
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Is the failure due to the particle break up model or the EOS? When you run it with ideal gas as an EOS does it work?
ghorrocks is offline   Reply With Quote

Old   March 31, 2015, 11:43
Default
  #3
cvh
New Member
 
Chait
Join Date: Apr 2014
Posts: 14
Rep Power: 12
cvh is on a distinguished road
I tried the same case with ideal gas EOS and it seems to work without any issues. So my guess is that it has to do something with the EOS...

For real gases, the properties are calculated by inverting the (h,s) table, so I have tried increasing the number of points in the table. But that hasn'w worked either! I have also tried supplying the initial conditions from the results for the ideal gas case..
cvh is offline   Reply With Quote

Old   March 31, 2015, 18:33
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,871
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
If you model the flow with the Peng-Robinson EOS but no particle breakup does it work?

Assuming the problem is the EOS - then you are going to have to use the normal general tricks to improve numerical stability. That means:
* Double precision numerics
* Improve mesh quality
* Improve mesh quality (I repeated this one because it is the most important )
* Smaller time step
* Better initial condition
ghorrocks is offline   Reply With Quote

Old   March 31, 2015, 20:07
Default
  #5
cvh
New Member
 
Chait
Join Date: Apr 2014
Posts: 14
Rep Power: 12
cvh is on a distinguished road
Thanks for the suggestions Glenn. Peng-Robinson EOS without particle breakup works on my current mesh, and I am already using double precision. I know that CFX calculates real gas properties from the (h,s) table. Also, this error message appears only while writing the backup/results file, and not after every iteration.

Anyways, I'll keep on experimenting with mesh quality and see if that makes any difference.
cvh is offline   Reply With Quote

Old   March 31, 2015, 20:12
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,871
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
If the error occurs during writing the results file then there is probably a specific variable in the results file which is causing the problem. If you change to "Selected Variables" and only include the variables you need to use in post-processing you just might side-step the problem.
ghorrocks is offline   Reply With Quote

Old   April 2, 2015, 13:15
Default
  #7
cvh
New Member
 
Chait
Join Date: Apr 2014
Posts: 14
Rep Power: 12
cvh is on a distinguished road
I increased the coefficients of restitution and now the simulation seems to be working. I think the solver was running into problems while solving for particles near the wall boundaries. Thanks for the help!
cvh is offline   Reply With Quote

Reply

Tags
newton solver, particle breakup, real gas


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
Particle tracking prob, urgent. sakurabogoda CFX 1 March 11, 2013 22:11
ATTENTION! Reliability problems in CFX 5.7 Joseph CFX 14 April 20, 2010 16:45
linear solver failure when using SST model fanzhong Meng CFX 4 March 21, 2006 21:16
compressible two phase flow in CFX4.4 youngan CFX 0 July 2, 2003 00:32
CFX 5.5 Roued CFX 1 October 2, 2001 17:49


All times are GMT -4. The time now is 03:50.