Abstract
This study investigates the acoustic performance of a system of two Helmholtz resonators experimentally and numerically. The distance between the Helmholtz resonators was varied to assess its effect on the acoustic performance of the system quantitatively. Experiments were performed using an impedance tube with two instrumented Helmholtz resonators and several microphones along the impedance tube. The relation between the noise attenuation performance of the system and the distance between two resonators is presented in terms of the transmission loss, transmission coefficient, and change in the sound pressure level along the tube. The underlying mechanisms of the spacing effect are further elaborated by studying pressure and the particle velocity fields in the resonators obtained through finite element analysis. The results showed that there might exist an optimum resonators spacing for achieving maximum transmission loss. However, the maximum transmission loss is not accompanied by the broadest bandwidth of attenuation. The pressure field and the sound pressure level spectra of the pressure field inside the resonators showed that the maximum transmission loss is achieved when the resonators are spaced half wavelength of the associated resonance frequency wavelength and resonate in-phase. To achieve sound attenuation over a broad frequency bandwidth, a resonator spacing of a quarter of the wavelength is required, in which case the two resonators operate out-of-phase.
Highlights
Broadband noise attenuation from aero-engines has become a challenging topic in the last decade for researchers from different backgrounds due to stringent noise emission regulations [1,2]
The effect of the spacing between two Helmholtz resonators mounted in an impedance tube is studied to explore its effect on the transmission loss and sound pressure level change
The experimental results showed that the presence of a second resonator can have profound effect on the acoustic performance of the resonator system, which depends on the location of the second resonator relative to the upstream resonator
Summary
Broadband noise attenuation from aero-engines has become a challenging topic in the last decade for researchers from different backgrounds due to stringent noise emission regulations [1,2]. Acoustic liners are the most common sound attenuating devices employed in controlling aero-engine noise, and consist of a perforated face sheet enveloping a sequence of cavities, creating a series of Helmholtz resonators. Multiple extended neck resonators within an acoustic liner would effectively attenuate a broad bandwidth of low-frequency aircraft noise. Following on from the recent surge in resonator positioning optimization studies for broad bandwidth sound frequency attenuation, such as Coulon et al [22], Cai et al [23], and Wu et al [24], the present work focuses on a detailed investigation into the effect of changing the spacing between two resonators and its impact on the transmission loss and transmission coefficient characteristics, as well as the change in sound pressure levels. This section aims to provide a detailed description of the experimental facility, test rig, measurement techniques, analytical model and numerical methods employed in this study
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
