1.5.1 Differences Between Interpreted and Compiled UDFs

The major difference between interpreted and compiled UDFs is that interpreted UDFs cannot access ANSYS FLUENT solver data using direct structure references; they can only indirectly access data through the use of ANSYS FLUENT-supplied macros. This can be significant if, for example, you want to introduce new data structures in your UDF.

A summary of the differences between interpreted and compiled UDFs is presented below. See Chapters  4 and 5 for details on interpreting and compiling UDFs, respectively, in ANSYS FLUENT.

• Interpreted UDFs
  • are portable to other platforms.

  • can all be run as compiled UDFs.

  • do not require a C compiler.

  • are slower than compiled UDFs.

  • are restricted in the use of the C programming language.

  • cannot be linked to compiled system or user libraries.

  • can access data stored in an ANSYS FLUENT structure only using a predefined macro (see Chapters  3).

• Compiled UDFs
  • execute faster than interpreted UDFs.

  • are not restricted in the use of the C programming language.

  • can call functions written in other languages (specifics are system- and compiler-dependent).

  • cannot necessarily be run as interpreted UDFs if they contain certain elements of the C language that the interpreter cannot handle.

In summary, when deciding which type of UDF to use for your ANSYS FLUENT model

• use interpreted UDFs for small, straightforward functions.

• use compiled UDFs for complex functions that
  • have a significant CPU requirement (e.g., a property UDF that is called on a per-cell basis every iteration).

  • require access to a shared library.