CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT > Fluent UDF and Scheme Programming

UDF changing the rate exponent of a reaction

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

LinkBack Thread Tools Search this Thread Display Modes
Old   September 16, 2009, 13:20
Default UDF changing the rate exponent of a reaction
New Member
Join Date: Sep 2009
Posts: 1
Rep Power: 0
Stefan H is on a distinguished road
Hi everyone I am new here!

I have a problem that I can not solve... Perhaps there is someone who can help me out?

I am using fluent 6.3 and I am simulating the combustion of a turbulent propane flame using the RSM in combination with the EDC.

There are 5 reactions in the combustion mechanism that I am using. One of these reactions is the reverse oxidation of hydrogen where the following is valid.

Reaction: H2O -> H2 + 0.5 O2
(A=xxx, Beta=xxx, Ea=xxx)
Reaction order: [H2]^-0.75[O2][H2O]

All reactions data are implemented by the standard GUI reaction panel.

What I would like to do in the UDF is to change the rate exponent for H2 to 1 instead of -0.75, if the concentration of H2 is lower than a specified value, say 10^-5. This is to prevent the reaction rate from becoming extremely large at low concentrations of H2, which leads to convergence problems.

I have been thinking about using the macro DEFINE_VR_RATE but maybe it is not possible to use with the EDC model? Is it possible to use DEFINE_NET_REACTION_RATE instead? One other possible way could perhaps be to add the modified reaction as a 6th reaction by means of the GUI panel and then have the udf to select the "right" reaction...

Could you please give me some advise?

Kind regards,
Stefan H is offline   Reply With Quote


combustion, edc, rate exponent, reaction

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
rate exponent changing Vitali FLUENT 0 July 27, 2007 11:40
case files UDF volumetric reaction rate Marie-Anne Main CFD Forum 2 February 24, 2006 09:43
UDF about reaction rate Julien FLUENT 0 June 30, 2005 12:23
reaction rate as UDF variable sivakumar FLUENT 4 February 12, 2002 00:31
chemical reaction - decompostition La S. Hyuck CFX 1 May 23, 2001 00:07

All times are GMT -4. The time now is 12:46.