On the Acoustic Performance of Double Degree of Freedom Helmholtz Resonator Based Acoustic Liners

Abhishek Gautam*, Alper Celik, Mahdi Azarpeyvand

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

8 Citations (Scopus)
3 Downloads (Pure)

Abstract

This study investigates the acoustic performance of double degree of freedom Helmholtz resonators and multi cell acoustic liners made of these resonators, both experimentally and through finite element analysis. The dimensions of the resonator internal cavities were varied to assess the effect of the volume ratio on the acoustic performance of the system. Experiments were performed using a grazing flow impedance tube and instrumented 3D printed modular resonators, which can be switched between a single and double degree of freedom resonating cavity configuration. An aluminium acoustic liner with 16 modular resonating cavities was also used in experiments. The effect of the volume ratio is investigated by presenting the transmission loss and transmission coefficient induced and the changes in sound pressure level within the resonator. The underlying sound attenuation mechanisms are further elaborated through the finite element analysis results of the acoustic pressure and velocity fields in the different resonator configurations. The results showed that as the volume ratio is increased, the difference between the first and second resonance frequencies tends to have a convex behaviour. This may indicate the presence of an optimum volume ratio of the two internal cavities for a broad bandwidth of sound absorption. Moreover, the finite element analysis results showed that increasing the volume ratio increased both the transmission loss induced and the bandwidth of frequencies attenuated at the first resonance frequency due to an in-phase velocity magnitude relation, for both the neck and septum of the resonator. Conversely, for the second resonance frequency, there is an out-of-phase relation between the neck and septum velocity magnitudes. In addition to the single resonator analysis, the acoustic performance of liner configurations with 16 resonators was also investigated. The results showed an increase in the bandwidth of attenuated frequencies when each resonating cavity had a different volume ratio, as compared to a fixed volume ratio. In addition, the order of the resonators of different volume ratio in the liner arrangement did not seem to have a significant effect on the overall sound attenuation performance.
Original languageEnglish
Article number108661
Number of pages14
JournalApplied Acoustics
Volume191
Early online date2 Mar 2022
DOIs
Publication statusPublished - 30 Mar 2022

Bibliographical note

Funding Information:
The research is supported by the European Commission through AERIALIST (AdvancEd aicRaft-noIse-AlLeviationdevIceS using meTamaterials), Grant agreement ID: 723367 and SilentProp, Grant agreement ID: 882842.

Publisher Copyright:
© 2022 Elsevier Ltd

Keywords

  • Helmholtz resonator
  • Linear acoustics
  • Impedance tube

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