Acoustic characteristics of a three-chamber hybrid silencer

Abstract

The acoustic characteristics of a hybrid silencer consisting of two identical single-pass, concentric, perforated dissipative chambers combined with a reactive Helmholtz resonator in between are investigated computationally and experimentally. Transmission loss predictions from a three-dimensional boundary element method are compared with experimental results obtained from an impedance tube setup in the absence of mean flow. In addition to the overall design, the effects of filling material density in dissipative chambers and the neck geometry of the reactive resonator are examined. The dissipative chambers are found to be effective at high frequencies, while the reactive resonator is shown, in general, to improve the acoustic attenuation at low frequencies typical of airborne noise in internal combustion engines running at low- to mid-speed range. The acoustic behavior near the resonance frequency is determined, however, to be sensitive to the duct length connecting dissipative and reactive chambers. Potential merits of the hybrid concept are assessed.