Passive Attenuation of Modal Cavity Aeroacoustics Under Supersonic and Transonic Conditions

Abstract

Open cavities exposed to a grazing flow can exhibit large pressure fluctuations, which may result in damage to stores or components carried within a weapon bay. This study investigates the use of passive resonant absorbers based on Helmholtz resonators to attenuate the problematic pressure fluctuations that arise in cavity flows, under both transonic () and supersonic () conditions. The experimental investigations indicate that resonant arrays can be used to provide attenuation levels of up to 26 dB within a cavity under supersonic () conditions. These supersonic designs were based on the properties of transonic devices, which also delivered high attenuation levels, with up to 15 dB attenuation for a single mode at Mach 0.95. A combined configuration with an array installed at both ends of the cavity, under supersonic conditions, provided attenuation levels up to 15 dB for multiple modes simultaneously, as well as a reduction in the broadband noise. This study investigates the attenuation mechanism for these devices, and discusses the effects of the high sound pressure levels, which arise within a resonant cavity, on the operation of the palliatives. A new semi-empirical model for resonant arrays under such acoustic environments is developed, and design guidelines of cavity applications are provided.