I just started using Fluent. Fluent has User Defined Function that gives much more flexibility on its applications. Now I am going to use UDF to put my own models and get them work in Fluent, but I have no idea how to do this since the UDF manual only tells you how to give your own BCs, Sources, etc. There is no single word talking about how to change or modify the conservation equations with UDF. I have seen from some open literatures that people had successfully done that with Fluent though. Anybody can give me any suggestions? Thanks a lot.

There are limits to what you can do - although with persistence you can do quite alot.

However, my advice, is if you want to solve very different equations write your own code or use another software. On the other hand, Fluent solves the fundamental conservation equations and you can add additional ones, so your models should be similar anyway.

To modify the conservation equations you write udfs for the source term, diffusion term, flux term and transient terms and BCs. This is discussed in the udf manual. For the inbuilt equations - eg. energy - you are limited in what you can do. In general you can't modify the transient term or the flux term in any direct way.

For scalar equations all these terms can be modified.

So your job would be to determine the differences between a FLUENT model and yours and write udfs to implement those differences inside Fluent.

Greg