Acoustic performance of a Helmholtz resonator with flow
The effect of flow on the acoustic characteristics of a Helmholtz resonator is investigated experimentally. An impedance tube set-up has been modified to facilitate the measurement of transmission loss in the presence of mean flow. Acoustic impedance of the resonator is also measured with and without flow, enabling the analysis of this parameter as well. Transmission loss directly measured from the improved impedance tube set-up is then compared with that calculated from the acoustic impedance. The results demonstrate that the flow effect on Helmholtz resonators is dramatic in terms of the resonance frequency and peak magnitude by shifting the peak transmission loss frequency to higher values and deteriorating the peak transmission loss magnitude (18.3% increase and 31 dB decrease, respectively, for Mach number, Ma = 0.1).
Keywords: Helmholtz resonator, flow effect, transmission loss, acoustics, vehicle noise, acoustic impedance