Optimizing gradient structural resonance compliant acoustic liner for duct-flow noise mitigation

Abstract

This study attempts to optimize the broadband low-frequency noise reduction using compliant acoustic liners in flow ducts. The analytical model for a single compliant unit is extended to multiple fluid-loaded compliant units acoustic liner mounted along a rigid duct wall in uniform duct flow. Each compliant unit is a tensioned elastic panel backed by a rigid cavity, and its fluid-loaded structural resonance is obtained by coupling the structural impedance of the panel with the acoustic impedance of the backing cavity. In the study, cavity depth and in-plane panel tension are treated as independent design variables that govern the location and bandwidth of transmission stopbands. A genetic algorithm is then employed to optimize the design variables over prescribed intervals, to maximize transmission loss over a target low-frequency band under geometric and structural constraints. The optimized liner designs show performance improvement in the location and width of the stopband. Moreover, it also confirms that optimized distributions of cavity depth and panel tension can merge multiple narrow resonant peaks into a broad low-frequency region of elevated transmission loss. The transmission loss (TL) stopband is effectively broadened from 0.043 ≤ f ≤ 0.07 in uniform resonance distribution configuration to 0.02 ≤ f ≤ 0.07 in the optimized design, thus providing an overall 85.0% increase in stopband bandwidth. The performance of the optimized design compliant liner is subsequently studied using high-fidelity time-domain direct aeroacoustic simulation for exploring the underlying aeroacoustic structural interaction.