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

The problem of Stiff Chemistry Solver in Multiphase model

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 2, 2015, 10:08
Default The problem of Stiff Chemistry Solver in Multiphase model
  #1
New Member
 
Yu-sen Niu
Join Date: Nov 2014
Posts: 16
Rep Power: 10
shenzhou1987 is on a distinguished road
Hello everyone!
I'm working on a project using ANSYS Fluent 13.0. In order to simulate the chemistry reactions between species, the Laminar Finite-Rate model is turned on. The Stiff Chemistry Solver and ISAT are used to make computation stable and fast. It works very well just in sing phase model. After that I bulid a mixture multiphase model which contains liquid water, then I find the Stiff Chemistry Solver disapper in Species Model Dialog, and I can't use ISAT also. This is bad, because the computation is very unstable without Stiff Chemistry Solver and ISAT, actually it diverges in a few iterations. I have tried Eulerian multiphase model, but it also doesn't work.
I find that the reactions can be created in 'Phase Interaction'->'Reactions' dialog. But the options that can be used is not too much, the 'Third-Body' can not be added into the reaction. And the Arrhenius React Rate can't be used in Mixture Multiphase, so I have to write udfs for the reaction rate. Although it is very complicated, I have fininshed this job finally. The udfs are compiled and loaded into the model. And the 'Heterogeneous Stiff Chemistry Solver' is used. But when I run the simulation, the Fluent reports these errors at the beginning.
ODE Solver failed in 14520 cells.
Mass_Diffusivity invalid(zero) diffusivity.
Please check material properties.
I have tried again and again, it's all the same. Then I turn off 'Heterogeneous Stiff Chemistry Solver', these errors are gone, and the simulation can go on, but the residual curve is very bad.
So does anyone have the same problem? And is it possilbe to use Stiff Chemistry Solver and ISAT in Mixture Multiphase model?
shenzhou1987 is offline   Reply With Quote

Old   January 11, 2016, 03:52
Default
  #2
Senior Member
 
Join Date: Jun 2014
Location: Taiwan
Posts: 100
Rep Power: 10
SJSW is on a distinguished road
I think you can first check the material properties, especially the properties of the mixture.
The mixing law you chose would be significant.
After recheck and modification, you can try to initialize and check the density or viscosity.

Heterogeneous Stiff Chemistry Solver in "Phase→Phase interaction→Reactions" should be checked.
This solver allowed the user to include inter-phase reaction and in-phase reaction.
The "Third-Body" can not be added into the reaction in "Phase→Phase interaction→Reactions," but you can add these reaction that using third body into Reactions and Mechanisms in Material property use "Species transport" Model.

However, some things need more clearification :
1. Could one add the same reaction in "Species transport" model and "Phase→Phase interaction→Reactions."
It seems no conflict? would the reaction rate be doubled?
2. The contour of Heterogeneous reaction rate is zero, but the reaction heat is not zero. I don't know why. Is the reaction rate too large? or the time step is too large? Confusing.
SJSW 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
about choosing Turbulence model for multiphase flow problem. Near FLUENT 5 April 11, 2019 05:24
CFX multiphase flow model aximefu CFX 24 February 17, 2018 06:35
Coupled VOF and Multiphase Segregated Flow for a gas bubble problem?? EnronZhang STAR-CCM+ 1 December 19, 2013 09:41
Stability problem due to turbulent dispersion force in a subcooled boiling model Edy OpenFOAM 7 August 10, 2011 13:00
problem with MFR model for multiphase mixing tanks Srinivas Main CFD Forum 1 November 7, 2005 15:16


All times are GMT -4. The time now is 01:30.