Rotorcraft Acoustic/Aerodynamics Analyses

The purpose of this SBIR project is to develop a rotorcraft acoustic solver that can treat long distance propagation through general, realistic environments. Only a Finite Difference Time Domain approach is capable of treating propagation through general inhomogeneous media, and only be considered outside the inner region (near the rotorcraft). However, the range limitation precludes the use of conventional formulations. This problem can easily be overcome by a new method, Wave Confinement (WC), developed by the proposed principal investigator. The basic idea of WC is first to extend the basic linearized Euler pde, by adding a nonlinear confinement term. This term results in thin stable, propagating structures, whose centroids propagate exactly as the pulses of the original unenhanced pdes. Also, the total amplitude, integrated along a ray, with geometric (azimuthal) spreading taken into account, is conserved. The difference is that pulse computed with WC has a profile defined by the computational method and not by the original, physical pulse profile. With WC (as with shock capturing methods), the important quantities involve conserved integrals through the thin shock, or pulse and the centroid location, but not profile. In addition, WC can treat reflections from obstacles in a very simple way.