A method for improving performance of a cavity resonance sound absorption structure based on lattice reflection

Abstract

A kind of cavity resonance sound absorption structure performance promotion method based on lattice reflection, based on the basic principle that phononic crystal local resonance generates band gap, by increasing the lattice outer frame, change the volume ratio of the volume of lattice outer frame and cavity resonance sound absorption structure, adjust the structure geometric parameters of lattice outer frame, produce double resonance system, and then obtain the sound absorption lattice that double sound absorption peak value appears in a certain working frequency range, reach the purpose of improving the sound absorption performance of original cavity resonance sound absorption structure, the results show that, the present application can make the average sound absorption rate in the frequency range of 200-10000Hz at least increase by more than 6 times.The present application not only has obvious sound absorption performance improvement effect, and does not need to design new sound absorption structure additionally, method is simple.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of noise reduction and sound absorption, and particularly relates to a cavity resonance sound absorption structure performance improvement method based on lattice reflection. BACKGROUND

[0002] The adverse effects of aircraft noise are reflected in all aspects. In terms of civil aviation, aircraft noise can cause cabin interior noise, which can cause discomfort to passengers and crew, and even health risks when the noise is too loud. For military aircraft, aircraft noise can reduce the stealth capability of the aircraft and restrict military combat capability. In addition, environmental noise pollution caused by aircraft noise has become a global concern. In 2018, the WHO "Environmental Noise Guidelines for the European Region" recommended reducing the noise level generated by aircraft to less than 45 decibels. In order to meet the noise standard, it is necessary to reduce the noise of modern aircraft.

[0003] Aircraft engine noise is the main source of aircraft noise, including fan noise, core engine noise and jet noise. With the increase of engine bypass ratio, the jet velocity gradually decreases, and the proportion of jet noise is also getting smaller and smaller. Fan noise has become the main noise source of modern large-bypass-ratio turbofan engines. Laying sound lining in the engine compartment is currently the most effective noise control method. Sound lining technology uses cavity resonance sound absorption structures such as perforated plates plus cavities to increase the acoustic impedance inside the aircraft engine, convert sound energy into kinetic energy of fluid, and then convert it into heat energy and diffuse to the surrounding environment to achieve sound reduction or elimination.

[0004] The inherent characteristics of traditional sound lining structures such as perforated plates and straight-through air back cavity determine their narrow sound absorption frequency band and weak low-frequency insertion loss. At the same time, the thickness of the perforated plate structure is comparable to the wavelength of the working frequency, which further hinders its application prospect in the field of low-frequency noise reduction. In addition, the traditional micro-perforated plate honeycomb sound lining structure has a huge difference in sound absorption efficiency and sound absorption frequency for sound waves incident from different directions, which leads to the need to consider the design of fluid machinery in the design of sound lining structure and coverage area, further increasing the design difficulty of sound lining structure. In addition, although in recent years, new types of cavity resonance sound absorption bodies based on acoustic metamaterials have emerged in an endless stream, such as thin film resonators and Helmholtz resonators, which can achieve good subwavelength low-frequency sound absorption effect, but the sound absorption frequency band is narrow, and this problem has not been effectively solved. SUMMARY

[0005] In order to solve the above problems, the purpose of the present application is to provide a cavity resonance sound absorption structure performance improvement method based on lattice reflection, based on the basic principle of band gap generated by phononic crystal local resonance, by increasing the lattice outer frame, changing the volume ratio of the lattice outer frame volume and the cavity resonance sound absorption structure volume, adjusting the structure geometric parameters of the lattice outer frame, generating a double resonance system, and then obtaining a sound absorption lattice with double sound absorption peak values in a certain working frequency range, so as to improve the sound absorption performance of the original cavity resonance sound absorption structure.

[0006] In order to achieve the above purpose, the technical scheme is adopted as follows:

[0007] A cavity resonance sound absorption structure performance improvement method based on lattice reflection, comprising the following steps:

[0008] (1) Obtain the overall size volume parameters of the original cavity resonance sound absorption structure 1, increase the lattice outer frame 2 outside the original cavity resonance sound absorption structure 1, and change the volume ratio n of the lattice outer frame 2 volume and the original cavity resonance sound absorption structure 1 volume, so that the sound absorption coefficient also changes;

[0009] (2) Generate a sound absorption coefficient cloud chart using the change result of the sound absorption coefficient, and select the n value corresponding to the sound absorption coefficient according to the sound absorption characteristics under the required working frequency;

[0010] (3) Adjust the structure geometric parameters of the lattice outer frame 2 according to the selected n value, and the lattice outer frame 2 and the original cavity resonance sound absorption structure 1 form a sound absorption lattice together, so that the sound absorption performance is improved.

[0011] The sound absorption lattice material is absolutely acoustically rigid, including metal materials such as 6061 aluminum, polymers such as PLA, and alumina ceramics.

[0012] The structure geometric parameter adjustment of the lattice outer frame 2 comprises the following steps:

[0013] (301) Determine that the inner width of the lattice outer frame 2 is equal to the overall width of the original cavity resonance sound absorption structure 1;

[0014] (302) According to the volume ratio n of the lattice outer frame 2 volume and the original cavity resonance sound absorption structure 1 volume, determine the remaining structure geometric parameters of the lattice outer frame 2 that need to be adjusted, including inner length, inner height and wall thickness.

[0015] The present application has the following beneficial technical effects:

[0016] The method is based on the basic principle of band gap generated by phononic crystal local resonance, and first uses an outer frame of lattice to improve the sound absorption performance of the cavity resonance sound absorption structure, and only needs to adjust the structural parameters of the outer frame of lattice 2 according to the value of n each time to generate a double resonance system, establish a sound absorption lattice, and improve the sound absorption performance. At the same time, the difficulty of designing the new sound absorption structure is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A sound absorption lattice structure model diagram for improving the performance of the neck-extended cavity resonance structure.

[0018] Figure 2 A cross-sectional view of the sound absorption lattice structure model.

[0019] Figure 3 A sound absorption coefficient diagram generated by the change of the ratio n of the volume of the outer frame of lattice to the volume of the outer contour of the cavity resonance structure.

[0020] Figure 4 A sound absorption coefficient comparison diagram of the improved sound absorption body based on the method of the application and the original neck-extended cavity resonance structure. DETAILED DESCRIPTION

[0021] The application will be further described in detail below with reference to the drawings.

[0022] The application provides a cavity resonance sound absorption structure performance improvement method based on lattice reflection. The method first uses a lattice frame for the performance design of the cavity resonance sound absorption structure. Taking the performance improvement design of the neck-extended cavity resonance structure as an example, the ratio of the volume of the outer frame of lattice to the volume of the cavity resonance sound absorption structure is selected, and by adjusting the structural geometric parameters of the outer frame of lattice, a sound absorption lattice with double sound absorption peaks in a certain working frequency range is obtained, so as to improve the sound absorption performance of the original cavity resonance sound absorption structure. The specific steps include the following steps:

[0023] Step 1: Obtain the overall size volume parameters of the original cavity resonance sound absorption structure 1, as shown in Table 1. An outer frame of lattice 2 is added outside the original cavity resonance sound absorption structure 1 to establish a sound absorption lattice model, as shown in Figure 1 , and the cross-sectional view is as shown in Figure 2 . After the ratio n of the volume of the outer frame of lattice 2 to the volume of the original cavity resonance sound absorption structure 1 changes, the sound absorption coefficient also changes;

[0024] Step 2: Generate a sound absorption coefficient cloud diagram using the change result of the sound absorption coefficient, as shown in Figure 3The n value corresponding to the sound absorption coefficient is selected according to the sound absorption characteristics at the required working frequency. In this example, in order to improve the sound absorption performance of the cavity resonance structure in the low frequency (<2000 Hz), the medium frequency (2000-5000 Hz) and the high frequency (>5000 Hz), the n value is selected as 1.42, 7.93 and 3.25 respectively.

[0025] Step 3: According to the selected n value, adjust the remaining geometric parameters of the lattice outer frame according to formula (1) to obtain a sound absorption lattice that improves the performance of the cavity resonance structure.

[0026]

[0027] In the formula, a1, a2 and a3 are the inner length, the inner height and the inner width of the lattice outer frame 2 respectively, and V is the volume of the original cavity resonance sound absorption structure 1. Adjust the lattice outer frame structure parameters according to formula (1) and the n value, and the lattice outer frame structure parameters corresponding to different n values are shown in Table 2.

[0028] The inner width a3 of the lattice outer frame 2 is equal to the overall width of the original cavity resonance sound absorption structure 1, as shown in Figure 1 .

[0029] In order to verify the performance improvement method of the cavity resonance sound absorption structure proposed in the application, the performance improvement design of the resonance structure of the application is simulated as follows:

[0030] The sound wave is normally incident into the sound absorption lattice structure, and the sound absorption coefficient of the structure is obtained by energy dissipation of the sound wave. Figure 4 The sound absorption coefficient variation curves of the neck-extended cavity resonance structure and the sound absorption lattice corresponding to different n values in the frequency range of 160-10000 Hz are given. By Figure 3 It can be seen that the average sound absorption coefficient of the original neck-extended cavity resonance structure in the full frequency range of 160-10000 Hz is only 0.04, and after the design of the method of the application, the average sound absorption coefficients of the sound absorption structures designed under n=1.42, 7.93 and 3.25 are 0.25, 0.39 and 0.40 respectively, and the sound absorption coefficient is increased by at least 6 times. The average sound absorption coefficients of the original neck-extended cavity resonance structure in the low frequency, medium frequency and high frequency are 0.07, 0.02 and 0.05 respectively. According to the design of n=1.42, the average sound absorption coefficient in the low frequency range is increased to 0.17, which is increased by 1.4 times; according to the design of n=7.93, the average sound absorption coefficient in the medium frequency range is increased to 0.29, which is increased by 13.5 times; according to the design of n=3.25, the average sound absorption coefficient in the high frequency range is increased to 0.61, which is increased by 11.2 times.

[0031] Table 1 Size parameters of the neck-extended cavity resonance structure

[0032]

[0033] Table 2 lattice out frame structure parameters corresponding to different n values

[0034]

[0035] It can be proved by the above supplementary parameter materials that the cavity resonance sound absorption structure performance improvement method provided by the application can effectively improve the sound absorption performance of the original cavity resonance sound absorption structure, obtain a double-resonance peak sound absorption lattice, and according to the sound absorption requirements of different frequency bands such as low frequency, medium frequency and high frequency, the sound absorption coefficient under the corresponding different frequency bands can be improved accordingly, and the variability is strong. The method provided by the application only needs to increase the lattice out frame outside the original resonance type sound absorption structure, without additional complex structure design, and the method is simple and effective.

Claims

1. A method for improving the performance of a lattice-based reflection cavity resonance sound absorption structure, characterized in that, It comprises the following steps: (1) Obtain the overall size and volume parameters of the original cavity resonance sound absorption structure (1), and increase the lattice outer frame (2) outside the original cavity resonance sound absorption structure (1). After the volume ratio n of the lattice outer frame (2) to the original cavity resonance sound absorption structure (1) changes, the sound absorption coefficient also changes; (2) Generate a sound absorption coefficient cloud chart using the change result of the sound absorption coefficient. According to the sound absorption characteristics under the required working frequency, select the n value corresponding to the sound absorption coefficient; (3) Adjust the structural geometric parameters of the lattice outer frame (2) according to the selected n value. The lattice outer frame (2) and the original cavity resonance sound absorption structure (1) together form a sound absorption lattice, so that the sound absorption performance is improved; The sound absorption lattice material is absolutely acoustically rigid, including metal materials such as 6061 aluminum, polymers such as PLA, and ceramic oxides such as aluminum oxide; The adjustment of the structural geometric parameters of the lattice outer frame (2) comprises the following steps: (301) Determine that the inner width of the lattice outer frame (2) is equal to the overall width of the original cavity resonance sound absorption structure (1); (302) According to the volume ratio n of the lattice outer frame (2) to the original cavity resonance sound absorption structure (1), determine the remaining structural geometric parameters of the lattice outer frame (2) that need to be adjusted, including the inner length, the inner height, and the wall thickness.

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