Overlapping modal and geometric symmetries for computing jet-engine inlet scattering

By examining the scattering from a cylindrical inlet terminated by a fan-like structure possessing discrete angular symmetry, it is found that only very limited intermodal coupling is possible. This fact is exploited in a hybrid finite element/modal scheme to develop a very efficient solution where only one slice of the geometry need be modeled. It is shown that a phase boundary condition at the interior walls of the mesh is sufficient for the complete solution of the problem. The implementation of the phase boundary condition is detailed for the full three-dimensional case, including special considerations for enforcing the boundary conditions along the axis. A simple example is shown for the sliced, hybrid finite element/modal scheme to validate the method