I am working with compressible gas flow on my post graduation. The geometry is not very complex. I've worked before in the field of radiation heat transfer with Fluent5 and had a very good experience. The first question is which CFD-code should be here used ? Can anyone explain me which advantages (quality and accuracy) do softwares like CFX in comparison to Fluent have?

(1). I don't encourage graduate students in CFD field to use any commercial codes at all. If possible, try to avoid using the commercial CFD codes in your graduate study. This is because sooner or later, someone will ask you exactly the same question again when you are out of the graduate school. And hopefully at that point, you will be able to tell a different story about how the problem should be solved in your own way. (2). After having said that, I think, first of all, you need to know how to deal with commercial CFD codes. The best way to do is to define your problem as clear as possible. Then talk to various CFD code vendors to get their opinion about your problem and their codes. This is the only practical way to get your problem solved. It is very simple, you know your problems and they know their codes. (3). If you are talking about the public relations, any of these general commercial CFD codes should be able to (or have the potential to ) solve any common fluid flow problems. (4). Your compressible gas flow problem needs to be defined first in terms of the Mach number. It does make a big difference whether it is subsonic compressible, transonic, supersonic or hypersonic.