A multi-layer overlapping structure for continuous broadband acoustic wave absorption at lower-frequencies

Abstract

This paper is concerned with the design of a multi-layer overlapping structure consisting of a series of cavities and necks for acoustic wave absorption within continuous broadband at lower frequencies. The acoustic absorber is designed as a periodic structure, whose fundamental units can be regarded as Helmholtz resonators. A finite element model based on the linearized Navier-Stokes equations is developed to evaluate the thermal and viscous dissipation of the absorber. To verify the acoustic absorption characteristics of the structure, a series of absorbers fabricated by 3D printing are tested in an impedance tube. The numerical solutions of the acoustic absorption coefficient are in good agreement with the experimental results. It is found that the coupling effect of the cavities and the necks strengthens the sound absorption performance of the absorber in a wideband at lower frequencies. Physical insights into the absorption mechanism of the overlapping structure due to the energy dissipation of the necks are provided. The effects of the geometrical parameters including length, width and radius of the absorber on the acoustic wave absorption of the structure are investigated. In order to verify the efficiency of the designed overlapping structure for noise control in practical applications, a number of absorbers are mounted inside a scaled payload fairing of a space launch vehicle. The results show that the inner noise of the payload fairing can be significantly reduced in a broadband with a maximum value of 40 dB.