Numerical Study of Noise Shielding by Airframe Structures

This study is motivated by the development of ultra-quiet advent aircraft that use jet noise shielding by the airframe. Current methods to predict shielding from aircraft surfaces rely on formulae developed for diffraction of sound from point sources. However, the jet noise source is distributed, directional, and with finite spatial coherence. Development of reliable predictive tools for jet noise shielding therefore requires a different approach. In this study we use the Boundary Element Method to assess progressively more complex interactions between sources and shields. For validation, we start with the classic problem of a plane wave interacting with a sphere. Shielding of a point source by a rectangular plate is compared with empirical formulae as well as experimental data. Finally, we examine the interaction of a wavepacket – simulating the jet noise source – with a rectangular plate. The wavepacket model appears to capture important elements of jet noise diffraction as measured in experiments.