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-   -   CARM as reduced mechanism in Fluent (http://www.cfd-online.com/Forums/fluent/45801-carm-reduced-mechanism-fluent.html)

Adrian August 21, 2007 13:13

CARM as reduced mechanism in Fluent
 
Hi, has anyone used a CARM reduced mechanism in Fluent? I would need some hints in how to couple it with the UDF subroutine DEFINE_VR_RATE. Thanks


Allan Walsh August 21, 2007 18:58

Re: CARM as reduced mechanism in Fluent
 
Have you considered using the CHEMKIN functionality in Fluent? Sure, we have used our own custom reduced mechanisms. Just make sure you are consistent on units used in your UDF.

Adrian August 22, 2007 03:46

Re: CARM as reduced mechanism in Fluent
 
Many thanks for your answer. I would have some more questions if you don't mind.My problem is that I only have the reduced mechanism as a CKWYP routine. However, the routine is written in C++, which I think is ok for the Fluent to read, but I'm quite unfamiliar (more exactly beginner) with this procedure. Do I have to declare the reactions myself in the Fluent panel, or does Fluent read the reactions by itself from the CKWYP? More, do I have to couple the CKWYP with the DEFINE_VR_RATE function from Fluent in order to be able to hook up the UDF?


Allan Walsh August 22, 2007 13:19

Re: CARM as reduced mechanism in Fluent
 
Ok, you are going to have a set of chemical reaction equations you want to model and also the associated kinetic data. This could come from experiments, literature values, or subsets of other data. Then, there are several ways to get this data into Fluent. As I understand it, importing it as CHEMKIN file is one way although I have not done it that way myself. Have you looked at the Fluent manual? Apparently, others do it this way.

A second way of entering the reaction data is to use the reaction input panel in Fluent. You enter the stoichiometry, coefficients, pre-exponential factors, temperature dependance, and activation energy. This can be tedious if you have lots of equations and unit conversions so it may be preferable to import the data directly (i.e. as a CHEMKIN file).

The third way is to write your own UDF like DEFINE_VR_RATE. The built in reaction rates are somewhat limited. Say, for example, if you want to use one reaction rate for one temperature range and another rate for a different temperature range, the basic version can't handle that. Or, if you want to change the stoichiometric coefficient as a function of the species concentration. For these cases, you could incorporate your own customized reaction schemes. (The kinetic data can still come from the reaction input panels in Fluent or put into the UDF directly).

Using UDFs is not simple. Even so the UDFs are written in C++ and your routine is also written in C++ that won't help, much. You still need to look at units, variable names, logic etc. You would probably want to budget several weeks or months to do something like this.


Adrian August 24, 2007 07:48

Re: CARM as reduced mechanism in Fluent
 
Many thans for your support.

Adrian


mjved August 29, 2007 16:42

Re: CARM as reduced mechanism in Fluent
 
hi adrian

have you been able to couple the CARM to fluent using VR_RATE?


Adrian August 30, 2007 03:31

Re: CARM as reduced mechanism in Fluent
 
Well, not really, still using some skeletal mechanism. Have you done it? Thanks for your question


mjved August 30, 2007 15:16

Re: CARM as reduced mechanism in Fluent
 
no..


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