i want to simulate flow around bullet, but i having problem for gun and bullet geometry such cleareance/gap between bullet and barrel, than pressure, energy, etc. can anyone help me??? I appreciate all replies. thx

There will not be any gap between the bullet and the barrel of any modern weapon. You can get bypass flow through rifling though. The bullets start out slightly larger than the bore diameter and get squeezed into it. Pressure can reach or exceed 60K psi (414 MPa), depending on the design. Energy can be up to 15K-20K lbf-ft.

are you sure??? so i can say that bullet diameter larger than bore diameter, then the bullet's motion can make inner surface of barrel scratch.

The bore is much harder than the bullet (steel vs. bare or jacketed lead), so the bullet isn't going to damage the barrel. It is the other way around. Eventually the bore of the barrel will erode somewhat, but that would typically take tend of thousands of bullets.

thanks for your help, can you help me an example?? i appreciate it much. thanks again ;]

I'm not sure what kind of example you want. I'm fairly sure that FLUENT is not capable of solving the problem you are asking about. Internal ballistics is extremely complex and involves a lot of mechanical behavior that FLUENT can't come close to simulating.