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

Large source term in species equation

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 3, 2011, 18:59
Default Large source term in species equation
  #1
New Member
 
Join Date: Jan 2011
Posts: 3
Rep Power: 15
MACFD is on a distinguished road
Hi ,
I am trying to add a large source term in species equation. I have two species one has a mass fraction of 3e-5 (particle phase). Diffusivity of particles is really samll (D=1e-8 m^2/s).

Fluent does not converge when my source term is really large compared to diffusion term. I tried to gradually add the source term as 1/50 of the term, then 1/40,... It converges up to 1/4 of the source term and does not work afterward.

Could anybody help me resolve this issue. My guess is that divergence happens due to upwinding. my source term is not defined for upwinding. Any though is appreciated.

Thanks,
MA
MACFD is offline   Reply With Quote

Old   January 3, 2011, 22:39
Default
  #2
Senior Member
 
Real Name :)
Join Date: Jan 2010
Location: United States
Posts: 192
Rep Power: 16
ComputerGuy is on a distinguished road
MA,

Have you tried lowering the under-relaxation factors for the species mass fractions, or perhaps lowered your time step size? Decrease the time step by an order of magnitude and see if you can't get it to work.

ComputerGuy
ComputerGuy is offline   Reply With Quote

Old   January 4, 2011, 02:23
Default
  #3
New Member
 
Join Date: Jan 2011
Posts: 3
Rep Power: 15
MACFD is on a distinguished road
COMPUTERGUY,

Thanks for your prompt reply. My case is steady state.
I lowered the under-relaxation factor and it converged. I should check the results though to see if they are rational.
Your suggestion was great. Thanks a lot.

MA
MACFD is offline   Reply With Quote

Old   January 4, 2011, 08:58
Default
  #4
Senior Member
 
Real Name :)
Join Date: Jan 2010
Location: United States
Posts: 192
Rep Power: 16
ComputerGuy is on a distinguished road
Definitely check the results. Any time you lower the URF, the residuals will drop. Thus, you can occasionally "force" the residuals lower than your convergence criteria. To be on the safe side, you can set the residual criteria to some very low value, then monitor the residuals to see that they plateau (or, monitor a value of interest and wait until it stabilizes).

ComputerGuy
ComputerGuy is offline   Reply With Quote

Old   January 4, 2011, 15:16
Default
  #5
New Member
 
Join Date: Jan 2011
Posts: 3
Rep Power: 15
MACFD is on a distinguished road
I lowered URF value for the species. As you mentioned, it lowered the residuals and I defined a really small value for convergence criterion.
Unfortunately, the results are not rational. Center line values look fine but near wall I get really high concentration values (particles) that do not seem correct.
I wonder if you have any other suggestions. Thanks a lot,

MA
MACFD is offline   Reply With Quote

Reply

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
Problem of SOURCE term gradient in UDS wind Fluent UDF and Scheme Programming 6 December 1, 2022 15:21
momentum source term zwdi FLUENT 14 June 27, 2017 16:40
Reaction Source Term in Steady Species transport equation cfdvenkatesh Main CFD Forum 0 August 19, 2010 10:28
OpenFOAM on MinGW crosscompiler hosted on Linux allenzhao OpenFOAM Installation 127 January 30, 2009 20:08
species source term reaction Andrew FLUENT 3 May 27, 2005 13:35


All times are GMT -4. The time now is 20:45.