CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Reaction rates

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

LinkBack Thread Tools Search this Thread Display Modes
Old   March 23, 2000, 11:55
Default Reaction rates
Szasz Robert
Posts: n/a
Dear All,

I'm using a methane-air mixture with 2 step reaction mechanism. Trying to modify the reaction rate by a UDF there was no change in the reaction rates (I checked the xy plots), even when I set the reaction rate to 0 in the UDF. I would have two questions: 1. What could be the problem? 2. What does a 'function hook' mean: the parameter (in my case the reaction rate) is calculated only by the UDF, or is calculated by Fluent and after that is modified by the UDF.

Thank you for any ideas, Robi
  Reply With Quote

Old   May 10, 2000, 06:06
Default Re: Reaction rates
Jason Norman
Posts: n/a
Altering the rate in a UDF will not show up as a change in reaction rates in the GUI. I presume that you are redifining the *rr and *rr_t rates in the UDF. My understanding is that Fluent calculates the reaction rate according to its data in the finite rate section of problem setup. It then invokes the UDF which adjusts the *rr and *rr_t values to your new chemistry rates etc. However, Fluent uses the initial or old *rr and *rr_t values in the reporting of 'reaction rates'(menu etc.).

The way around this is to define a scalar in the UDF(for your new reaction rate). This scalar can then be plotted etc. (you don't need to solve the scalar since it is updated in the UDF).

As you probably realise, this is quite an inefficient way of adding a reaction rate UDF since the code effectively does the chemistry calculation twice. Fantastic!
  Reply With Quote


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
External Chemistry Solvers and Internal Reaction Rates mturcios777 OpenFOAM 6 May 17, 2013 07:11
Segmentation fault in running alternateSteadyReactingFoam,why? NewKid OpenFOAM 18 January 20, 2011 16:55
combustion - reaction rates - urgent help needed siri Main CFD Forum 2 March 3, 2007 12:25
EDC l- Reaction Rates are Zero for some Reactions Atul FLUENT 2 October 7, 2005 10:38
chemical reaction - decompostition La S. Hyuck CFX 1 May 23, 2001 00:07

All times are GMT -4. The time now is 13:00.