1.2 Why Use UDFs?

UDFs allow you to customize ANSYS FLUENT to fit your particular modeling needs. UDFs can be used for a variety of applications. Some examples include

• customization of boundary conditions , material property definitions, surface and volume reaction rates , source terms in ANSYS FLUENT transport equations, source terms in user-defined scalar (UDS) transport equations , diffusivity functions , etc.

• adjustment of computed values on a once-per-iteration basis

• initialization of a solution

• asynchronous (on demand) execution of a UDF

• execution at the end of an iteration, upon exit from ANSYS FLUENT, or upon loading of a compiled UDF library

• postprocessing enhancement

• enhancement of existing ANSYS FLUENT models (e.g., discrete phase model, multiphase mixture model, discrete ordinates radiation model)

Simple examples of UDFs that demonstrate usage are provided with most DEFINE macro descriptions in Chapter  2. In addition, a step-by-step example (mini-tutorial) and detailed examples can be found in Chapter  8.