Regarding Coding in CFD
 

If I want to access the CFD code in any commercial Software, Then How should I do the same?
What are basic prerequisites for CFD coding?
Usaully in which Language the codes have been written??

generally commercial codes allows simple coding adding in their software through user defined funtions.
In Ansys Fluent it's a kind of C language
In Star CCM+ it is in fortran I think.

Fluent allows access to flow variables and parameters using the UDF framework. Obviously this won't help you if you're looking to see the 'nuts and bolts' of the solver itself, but it does provide a useful way of adding on your own pieces of code.

Pre-defined macros allow access to solver variable quite intuitively and also includes loops across the entire domain.

I hope that goes some way to answering your question!

By using OpenFoam CFD code ,yoy can access open cfd source codes even for main routines