International Research Fellowship Program: Aeroacoustic Model for an Elastic Lifting Surface with a Soft, Sound Absorbant Coating: The Silent Flight of Owls

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0965248JaworskiThe International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four-month research fellowship by Dr. Justin Jaworski to work with Drs. Nigel Peake and Timothy J. Pedley at the University of Cambridge in the UK.Owls employ multiple noise suppression features to reduce their acoustic signature within the hearing sensitivity of their prey, much of which is shared by human audition. Two of these noise suppression features, a soft, fibrous velvet material located at certain areas of a wing and an elastic, serrated trailing edge, are thought to work in concert to reduce the effect of background turbulence on noise scattering and to dissipate sound within a large frequency bandwidth. Despite recent efforts to quantify the aeroacoustic effect of a soft coating experimentally, a viable theoretical model does not currently exist. The present research systematically addresses the aeroacoustic impact of these noise suppression mechanisms and isolates the impact of porous media acoustics from the aerodynamic influence of the velvet coating on the flow field. In this manner, the results from the proposed research can be compared directly against experiment and state-of-the-art aeroacoustic computations. Each of the owl noise suppression mechanisms is reduced to physically consistent models that extend analytical aeroacoustics results in the research literature, culminating in a generalized and unified aerodynamic and aeroacoustic framework for a novel computational design tool. The design tool and principles developed from this work will enable quieter future designs for fixed and flapping wing micro air vehicles (MAVs) that operate in flow regimes similar to owls. Lessons learned from this research may also inform sound reduction techniques for lifting surfaces at higher Reynolds and Mach numbers including functionally-silent air vehicles.