In this case, we wanted to add a boundary condition in temperature on the wall.
Firstly, we wrote a User-Defined Function (UDF), that is to say a program using macros written in the C programming language (it has to pe put in the working directory).
To do this, we invite people to read the help of FLUENT (what you want to do is already inside).
Here, we defined a program which calculate the temperature in function of the abscise x (x means that the origin of the reper is on the left side)
Once the UDF is written, we compiled it with interpreted... (of course !).
Here, there is just to add the name of the program and to click "Compile".
Now, the UDF is available. We can use it as a boundary condition on the walls.