Double Degree of Freedom Helmholtz Resonator Based Acoustic Liners

TL;DR

This study investigates double degree of freedom Helmholtz resonator acoustic liners through numerical simulations and experiments, aiming to enhance sound attenuation understanding and identify optimal cavity configurations for broader bandwidth absorption.

Contribution

It introduces a combined numerical and experimental analysis of double degree of freedom Helmholtz resonators, revealing potential for optimized broadband sound absorption.

Findings

Good agreement between experimental and numerical data

Changing internal chamber dimensions affects resonance peaks

Optimal cavity volume ratio may enhance broadband absorption

Abstract

A numerical and experimental study on double degree of freedom Helmholtz resonator based acoustic liners is performed in this paper, with the motivation to improve the understanding of their sound attenuation mechanism. A single degree of freedom liner is designed and manufactured, as baseline, to compare with the double degree of freedom acoustic liners. The Grazing Flow Impedance Tube Facility at Bristol is used to measure the transmission coefficients of the acoustic liner samples, which are compared against data obtained via numerical simulations on Comsol. Both sets of data show good agreement. The effect of changing the internal chamber dimensions is studied numerically, through Comsol steady state simulations, followed by time domain simulations. A minimum, in the difference between the primary and secondary resonance peaks is observed. This may be an indication of the presence of an optimum volume ratio of the two internal cavities in the double degree of freedom resonator, for a broad bandwidth sound absorption.