Hi, every body; I am a fresh user of writing UDF. I have some questions I am confused now. I appreciate all relpy.

The problem i want to solve is to add a source term in the mass balance equation. The source term is the following:

source=dq/dt dq/dt=k(q*-q)

q* is the function of concentration

1. Do I need to use user defined scalar?

2. In the source term subroutine, is it necessary to define ds?Sometimes, ds is too complex, can i not write it?

3. This is a multicomponet problem. I do not understand what the meaning of int i in some solution variables.Is it can be written 1 or 2 to represent differnet species?

By the way, I would like to read more documents about udf. But I have only Fluent5 udf user guide, 2000. Could you provid more documents online?

Thank you very much

Frank

Hi,

first upgrade to Fluent 6 and get the udf manual that comes with this version. This is the best documentation for udfs.

There is a udf manual for v5 too. \

(These are located on the documentation CDs which you should have - but which many system admins like to ignore!!!! Who needs docs???? - unfortunately this logic doesn't work with CFD programs which are very complex)

To answer your questions 1. no, unless q itself needs a pde to solve 2. you can often ignore ds, but stability is improved if you use it. note that ds should either be zero or negative. Positive values need to be linearised out - see Patankar 3. i refers to the ith species - counting from zero (or some other index eg. uds scalar in other macros)

Hope it helps

Greg

Greg,Thank you very much!!! I will ask you other question later.

Thank you again

Frank