Abstract
Side branch Helmholtz resonators (HRs) are widely used to control low frequency tonal noise in air duct system. The passive Helmholtz resonator only works effectively over a narrow frequency range around resonance frequency. Changes in the exciting frequency and temperature will decrease the noise reduction performance. Many studies have been conducted on incorporating a Helmholtz resonator with active noise control to tuning the resonance frequency of HRs. The objective of this study is to study the effect of flow on the semi active Helmholtz resonator for duct noise control. Owing to a low Mach number air flow, the discontinuity condition at the joint is analytically formulated according to the conservation of the momentum and mass of air flow. Based on the transfer function at the junction, a controller function is proposed to tune the semi-active Helmholtz resonator under flow condition.
Highlights
Helmholtz resonators are often used in duct system to control low frequency noise
Many studies have been conducted on incorporating a Helmholtz resonator with active noise control to tuning the resonance frequency of Helmholtz resonators (HRs)
The objective of this study is to study the effect of flow on the semi active Helmholtz resonator for duct noise control
Summary
Helmholtz resonators are often used in duct system to control low frequency noise. It consists of a small neck and a cavity. Changes in exciting frequency and temperature result in the inconsistent between the noise source and HRs and decrease the effectiveness of the HRs. In order to adapt to the changes, a solution is integrating the Helmholtz resonator with active control system. Radcliffe and Birdsong [6] proposed an electronically tuned semi-active Helmholtz resonator They controlled the acoustic impedance of the resonator through mounting a loudspeaker at the end of the HR. Anderson [10] measured the acoustic impedance of a single side branch HR in a circular flow duct and found that fundamental frequency increased with increasing flow while neck end correction decreased. This paper aims at studying the effect of flow on the semi active Helmholtz resonator for duct noise control. The control controller transfer function under flow condition is proposed
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