The STL is not a CFD mesh, just a way to digitize a surface or volume. The CFD mesh consists of 3D elements in the shape of a tetrahedral, a hexadral, or wedge element. The mesh can be exported from a Fluent model. The exact shape of the air domain solved in Fluent is available to be solved again and the surface of the wing is represented exactly in that mesh. 

Can you see the Fluent CFD mesh? I suspect that the size of the elements used to solve the Fluent model are smaller than the size of the facets of the STL file. Can you confirm that? If what I suspect is true, the STL file may have significant errors in the geometry compared to the mesh used by Fluent. It is worth expending some effort to get that mesh.