Low-frequency noise reduction of rocket fairings using horn-shaped-neck helmholtz resonators

The low-frequency noise attenuation technology inside rocket fairings using Helmholtz resonators with hornshaped neck is constructed. The acoustic performance of a Helmholtz resonator with horn-shaped neck is investigated by methods combining theory, simulation, and experiment. A one-dimensional analytical method is developed to determine the resonance frequency under rigid-wall assumption, whereas an electroacoustic analogy approach is applied to consider the effect of compliant wall, and the theoretical analysis is verified by three-dimensional finite element method. Moreover, the influence of different neck types and wall thickness on the resonance frequency is compared. The main mechanism of sound absorption of a Helmholtz resonator is also studied, and experimental verification on this is carried out in an impedance tube. Results indicate that the resonant frequency can be controlled by neck shape and wall thickness, and the viscous damping at the neck is the main noise-reduction mechanism of this kind of Helmholtz resonator. The finite element model of a rocket fairing is established, and the response characteristic of a fairing cavity is obtained, based on which the certain size horn-shaped-neck Helmholtz resonators are designed and made out. The availability of Horn-shaped-neck Helmholtz resonators on low-frequency noise reduction is demonstrated by test and simulation.