That is a good comparison Aras, I agree that the STL file is fairly accurate representation of the Fluent mesh rigid surface of the wing. There is a small difference between a twisted quad element face and two triangular faces, but at least there is not a huge difference.
I am not expert at Fluent, but a fluent .msh file is just a stripped down .cas file.
Try the following to get the .msh file from .cas file:
1. In Fluent Solution Mode (normal mode), write a .cas file
2. Launch Fluent in the Meshing Mode by ticking “Meshing Mode” in the Fluent Launcher
3. Read the .cas file just saved by File>Read>Mesh… then it prompt “Reading a case file as a mesh file results in loss of boundary conditions.” Press OK.
4. Write the mesh as .msh by File>Write>Mesh…