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

 February 23, 2006, 11:37 Adjust reaction rates #1 Martin Skov Rasmussen Guest   Posts: n/a I want to model a chemically reacting flow. The flow is laminar and involves 6 species in 4 reactions. The rate expressions I have at hand do, however, not comply with the modified Arrhenius expression applied in Fluent although "my" rate expressions only differ by a multiplication of an additional term (1-B). r = k*T^n*exp(-Ea/RT)*(1-B) Does anyonw know if it is possible to simply make an adjustment in UDF of the rate calculated by Fluent? I have considdered to make the adjustment via the macro DEFINE_VR_RATE... Any help?

 February 27, 2006, 03:42 Re: Adjust reaction rates #2 RoM Guest   Posts: n/a Is (1-B)=const ? In this case you could include it in k. RoM

 February 27, 2006, 07:07 Re: Adjust reaction rates #3 Martin Skov Rasmussen Guest   Posts: n/a No, B is a function of species concentrations and thermodynamic properties, but I have all these data and properties at hand and can easily write this into a UDF...

 February 27, 2006, 07:58 Re: Adjust reaction rates #4 RoM Guest   Posts: n/a In this case a DEFINE_VR_RATE udf would be the best option. RoM

 February 27, 2006, 08:49 Re: Adjust reaction rates #5 Martin Skov Rasmussen Guest   Posts: n/a I have tried this using an interpreted as well as compiled version and both fails to run. I recieve an error during the first iteration. Do you know if a turbulence model must be invoked in order for the UDF to work. Even the example IU have found in the UDF manual seems to fail when the flow is laminar...

 February 27, 2006, 11:11 Re: Adjust reaction rates #6 HS Guest   Posts: n/a If not already doing so, try assigning values to both *rate and *rr_t (FLUENT will pick the limiting one as in the Eddy Viscosity model), i.e. *rate = (whatever your formula is); *rr_t = *rate; Maybe this helps! /Henrik

 February 28, 2006, 06:27 Re: Adjust reaction rates #7 rom Guest   Posts: n/a Have you tried the soultion procedure outlined in the fluent manual? Try to start with a cold flow solution with no reactions and then gradually add the reactions one by one. If the system is numerical stiff it will then start to diverge and you need to use the stiff chemistry solver. RoM

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post NewKid OpenFOAM 18 January 20, 2011 17:55 siri Main CFD Forum 2 March 3, 2007 13:25 Atul FLUENT 2 October 7, 2005 10:38 La S. Hyuck CFX 1 May 23, 2001 00:07 Szasz Robert FLUENT 1 May 10, 2000 06:06

All times are GMT -4. The time now is 12:43.