Noise Attenuation Using Acoustic Resonators: A Multifactorial Investigation and Characterisation of Performance Factors

Unwanted or harmful sound is considered noise. If not addressed, it can cause psychological and physiological harm and have detrimental effects on structures and machinery. Despite the widespread use of acoustic resonators for noise reduction, there remains a lack of comprehensive understanding of the circumstances under which their full potential can be realised. The complexity of this challenge can be attributed to the large number of potential performance-affecting parameters. As a result, the amount of associated literature dealing with such acoustic properties is generally overwhelming.This thesis compiles comprehensive, application-agnostic information on the performance factors of acoustic resonators, aiming to enhance their effectiveness across a wide range of contexts. Through an extensive literature review, this work identifies and assesses the known influence and significance of performance factors, pinpointing critical gaps in the current understanding. Subsequently, bespoke acoustic experiments are meticulously designed and conducted to evaluate existing theories and enhance the characterisation of performance-defining factors.The experimental test matrix comprises two distinct acoustic resonator configurations. The first configuration features interchangeable discrete apertures and a variable cavity volume, while the second configuration includes a fixed cavity volume and interchangeable plates with varying distributions of apertures. Acoustic measurements are collected for both configurations under a wide range of geometric and flow conditions variations, which results in a significant database of attenuation performance metrics against corresponding design and environmental variables.Experimental findings are supplemented with a separate computational fluid dynamic investigative methodology, which is validated against the collected measurements, and utilised to provide additional insight into the intrinsic dynamics in the vicinity of the resonator neck.Novel insight into the applicability of existing analytical models in an applied context is demonstrated, highlighting and quantifying the significance of previously underappreciated performance factors, and providing empirically derived deductions to improve the current state of the art.