Abstract
In order to solve the problem of low-frequency noise of aircraft cabins, this paper presents a new Helmholtz type phononic crystal with a two-dimensional symmetric structure. Under the condition of the lattice constant of 62 mm, the lower limit of the first band gap is about 12 Hz, and the width is more than 10 Hz, thus the symmetric structure has distinct sound insulation ability in the low-frequency range. Firstly, the cause of the low-frequency band gap is analyzed by using the sound pressure field, and the range of band gaps is calculated by using the finite element method and the spring-oscillator model. Although the research shows that the finite element calculation results are basically consistent with the theoretical calculation, there are still some errors, and the reasons for the errors are analyzed. Secondly, the finite element method and equivalent model method are used to explore the influence of parameters of the symmetric structure on the first band gap. The result shows that the upper limit of the first band gap decreases with the increase of the lattice constant and the wedge height and increases with the increase of the length of wedge base; the lower limit of the band gap decreases with the increase of the wedge height and length of wedge base and is independent of the change of lattice constant, which further reveals the essence of the band gap formation and verifies the accuracy of the equivalent model. This study provides some theoretical support for low-frequency noise control and broadens the design idea of symmetric phononic crystal.
Highlights
During take-off and flight, aircraft will produce huge noise, especially the lowfrequency noise, which will seriously affect the physical and mental health of flight personnel and ground crew [1] and cause acoustic fatigue of the aircraft structure and electronic equipment [2]
In order to study the sound insulation performance of this structure and compare the similarities and differences between the actual structure and the simulation model, a two-dimensional model of the periodic phononic crystal structure was constructed in this paper
It will lead to the reduction of the equivalent stiffness k1 and k210ofofthe spring in the equivalent model, that the upper and lower limits of the first band gap continued to decrease. These results showed that the increase of the wedge height h will lead to the upper and lower limits of the first band gap moving to the direction of low hfrequency
Summary
During take-off and flight, aircraft will produce huge noise, especially the lowfrequency noise, which will seriously affect the physical and mental health of flight personnel and ground crew [1] and cause acoustic fatigue of the aircraft structure and electronic equipment [2]. The low-frequency noise energy in a turboprop aircraft cabin is mainly concentrated in 0~500 Hz [3]. It cannot be effectively controlled by the conventional sound insulation materials currently applied due to the long wavelength of low-frequency noise [4]. In order to solve such noise problems of aircraft cabins, it is important to isolate the noise in the propagation path. Since aircraft has high requirements for structural strength and weight, it is critical to study and use a low-frequency sound insulation structure with lightweight and low density to isolate the noise in the process of noise propagation [5].
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