Maybe you can convert .stl to .stp using Solid works, and than import that .stp file into Fluent to get .msh format, I am not 100% sure if this work, but you can try.
Oh, it is very complicate model and this stl model have very sharp edges. If you can, send me stl file to try to do that, but I not guarantee that I can make it. I want to help if I could.