Development of a Lightweight, Low Frequency Acoustic Barrier with Spherical Particles for Fairing Noise Control

Abstract

The acoustic environment during launch is severe and damaging to critical spacecraft components. Sound pressure levels can exceed 130 dB. Conventionally, special acoustic insulation is used for damping out these high acoustic loads; however, they are ineffective below 500 Hz. In this paper, we present an alternative lightweight acoustic barrier employing particulate interaction in a foil layer. It was theorized that the presence of spherical particles in the foil would enable the excitation of bending waves in the plane of the foil causing inter-particle interactions. Essentially, the foil would act as a dense sound barrier over a narrow frequency range. Blankets were fabricated and tested in a standing wave tube, a resonant enclosure, and a Chamber Core fairing. In the standing wave tube and resonant enclosure tests, the particle embedded foil blanket improved the acoustic performance between 300 and 500 Hz. However, in the Chamber Core tests the improvement occurred between 475 and 625 Hz. The difference is attributed to the different test setups and the attachment method used.