Hello, has somebody used fortran routines in fluent and how they are used in fluent, e.g. in case of adding own fluid property (density, viscosity etc.) correlations ? i did not find enough information about Fluent 4.5 User Guide Manual even about the installation of fortran compiler.

As far as I know the functions have to be written in C

In Fluent 4.5 you have to compile your own version of Fluent code where you have your own subroutines with the code. Find a Makefile somewhere in your fluent4.5-directory and use it for compiling. There are instructions how to add own source terms in Fluent 4.4 manual Vol. 4, Chapter 20.

In Fluent 5 (UNS) there is (unfortenately) no way to add Fortran subroutines to the code. In principle it is possible to call Fortran routines from C-routines, but you have anyway to build an interface between Fluent platform and your subroutine. Then you have to use compiled routines, not interpreted option.