Low-frequency muffling guide vane, guide vane muffling device and muffling frequency adjusting method

Abstract

This invention discloses a low-frequency noise-absorbing guide plate, a noise-absorbing device, and a noise-absorbing frequency adjustment method. The low-frequency noise-absorbing guide plate includes an arc-shaped shell. One side of the outer arc surface of the shell is a rigid skin, and the other side is a perforated plate skin. The shell is divided into multiple independent cavities along its arc length. At least one first cavity contains a detachably mounted low-frequency sound-absorbing module. The panel of the low-frequency sound-absorbing module has through holes and forms a closed resonant cavity with the shell, constituting a resonant sound-absorbing structure. At least one second cavity is filled with resistive sound-absorbing material. The low-frequency sound-absorbing modules include various specifications with different frequencies. The noise-absorbing frequency characteristics can be adjusted by changing the module specifications or adjusting the module installation position. This invention integrates resonant sound absorption and resistive sound absorption within the guide plate. Within the 50Hz~200Hz frequency band and with a frequency resolution of 1Hz, the transmission loss at each frequency point is no less than 12dB. Furthermore, the structure is simple and the frequency is adjustable, making it suitable for low-frequency noise reduction in areas such as wind tunnel corners.

Description

Technical Field

[0001] This invention relates to the field of ventilation noise reduction technology, specifically to a low-frequency noise reduction guide plate that combines airflow guidance and low-frequency noise reduction functions, a flow guiding and noise reduction device including the low-frequency noise reduction guide plate, and a method for adjusting the noise reduction frequency of the low-frequency noise reduction guide plate. Background Technology

[0002] like Figure 1 As shown, a silencer vane is a special type of plate silencer, widely used in the corner sections of wind tunnels, ventilation and air conditioning systems, etc., to achieve noise reduction while ensuring smooth airflow deflection (guidance). Taking a wind tunnel as an example, the corner vane is a key component for achieving airflow deflection. Noise generated by the main noise sources such as the wind tunnel fan system propagates along the air duct and needs to be suppressed along its propagation path. The corner section is an ideal location for silencing structures.

[0003] Existing noise-reducing guide vanes are generally improved versions of resistive plate silencers: the vane's shape is designed according to corner angles, the interior is filled with resistive sound-absorbing materials such as glass wool and rock wool, and the sides are covered with perforated plates. The noise reduction performance of these vanes is similar to that of plate silencers, exhibiting low noise reduction below 500Hz, higher noise reduction between 500Hz and 2000Hz, and a decrease in noise reduction above 2000Hz due to high-frequency failure. However, low-frequency noise energy from noise sources such as wind tunnel fans is prominent, and the need for noise reduction in the 50Hz-200Hz frequency range is particularly urgent; existing resistive noise-reducing guide vanes are insufficient to meet low-frequency noise reduction requirements.

[0004] On the other hand, while resonant sound-absorbing structures such as Helmholtz resonators and perforated plate resonators have good low-frequency sound absorption performance, they are mostly used as independent components in pipe silencers, and there are no mature solutions for structural integration with corner guide vanes. Although acoustic metamaterials can achieve good sound absorption in the low-frequency range, their complex structure and high manufacturing cost limit their engineering application value. In addition, the sound attenuation performance evaluation of existing silencer guide vanes is usually based on 1 / 1 octave or 1 / 3 octave. Even if the octave attenuation meets the standard, it cannot be guaranteed that each frequency point within the frequency band (e.g., when the frequency resolution is 1Hz) has sufficient sound attenuation, resulting in the problem that the sound attenuation at individual frequency points within the octave is significantly low.

[0005] Therefore, how to provide a noise reduction guide plate that has high transmission loss at each frequency point in the low frequency band of 50Hz~200Hz and whose noise reduction frequency can be adjusted according to needs is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing noise-absorbing guide vanes in terms of insufficient low-frequency noise reduction performance and non-adjustable noise reduction frequency, this invention provides a low-frequency noise-absorbing guide vane, a flow-guiding noise reduction device, and a noise reduction frequency adjustment method. The aim is to achieve higher transmission loss at each frequency point within the low-frequency range of 50Hz to 200Hz under the condition of a frequency resolution of 1Hz, and to make the noise reduction frequency characteristics flexibly adjustable according to the target noise spectrum.

[0007] To address the aforementioned technical problems, this invention provides a low-frequency noise-absorbing guide plate, comprising an arc-shaped shell, the arc-shaped shell having a rigid skin on one side of its outer arc surface and a perforated plate skin on one side of its inner arc surface; the arc-shaped shell is divided into multiple independent cavities along its arc length by multiple partitions, the multiple cavities including at least one first cavity and at least one second cavity; a low-frequency sound-absorbing module is disposed in the first cavity, the low-frequency sound-absorbing module comprising a housing, the housing having a through hole on a panel facing the perforated plate skin, the panel and the housing forming a closed resonant cavity, the through hole and the resonant cavity constituting a resonant sound-absorbing structure, sound waves can enter the resonant cavity through the perforated plate skin and the through hole; the second cavity is filled with resistive sound-absorbing material.

[0008] Preferably, the low-frequency sound-absorbing module is detachably installed in the first cavity; the low-frequency sound-absorbing module includes various specifications, and the low-frequency sound-absorbing modules of different specifications have different numbers of openings, opening diameters, opening positions and perforation rates of the through holes, and / or different volumes of the resonant cavity, so that the low-frequency sound-absorbing modules of different specifications have different resonant frequencies.

[0009] Preferably, there are multiple first cavities, which are arranged along the arc length of the arc-shaped shell, and the low-frequency sound-absorbing modules installed in at least two of the first cavities have different specifications.

[0010] Preferably, a mounting frame is provided inside the arc-shaped housing, and the low-frequency sound-absorbing module is detachably connected to the mounting frame by fasteners.

[0011] Preferably, the panel includes a perforated section and a rigid section, and the through hole is formed in the perforated section; the through hole on the perforated section and the resonant cavity constitute a Helmholtz resonant sound-absorbing structure, and the rigid section and the expansion space in the first cavity constitute an expansion cavity sound-absorbing structure.

[0012] Preferably, the inner wall of the resonant cavity is attached with a resistive sound-absorbing layer, and a protective plate is provided on the side of the resistive sound-absorbing layer facing the resonant cavity. The protective plate is a perforated plate.

[0013] Preferably, the diameter of the through hole is 3mm to 12mm, and the perforation rate of the panel is 25% to 30%.

[0014] Preferably, there are nine cavities, numbered sequentially from the front edge to the rear edge of the arc-shaped shell as cavities 1 to 9, wherein cavities 1 to 5 are the first cavities, and cavities 6 to 9 are the second cavities.

[0015] Preferably, the resistive sound-absorbing material is glass wool with a density of 32 kg / m³; the perforated plate skin has a pore size of 3 mm and a perforation rate of 25%; the arc of the arc-shaped shell is 90°, and the leading edge is streamlined.

[0016] Preferably, within the frequency band of 50Hz to 200Hz and with a frequency resolution of 1Hz, the transmission loss of the low-frequency noise-absorbing guide plate is not less than 12dB.

[0017] The present invention also provides a flow guiding and noise reduction device, comprising a plurality of the above-mentioned low-frequency noise reduction guide plates arranged in parallel, wherein an airflow channel is formed between two adjacent low-frequency noise reduction guide plates.

[0018] The present invention also provides a method for adjusting the silencing frequency of a low-frequency silencing guide plate, based on the aforementioned low-frequency silencing guide plate, comprising: selecting a low-frequency sound-absorbing module with a corresponding resonant frequency from a variety of low-frequency sound-absorbing modules according to a target silencing frequency, and installing the selected low-frequency sound-absorbing module in a first cavity; and / or adjusting the installation position of the low-frequency sound-absorbing module in multiple first cavities to adjust the transmission loss of the low-frequency silencing guide plate at each frequency point.

[0019] Beneficial effects

[0020] (1) Excellent low-frequency broadband noise reduction performance. This invention integrates a resonant sound-absorbing structure and a resistive sound-absorbing structure inside the guide plate: the low-frequency sound-absorbing module in the first cavity absorbs low-frequency sound energy in a targeted manner using a "through-hole-resonant cavity" resonant sound-absorbing structure, while the resistive sound-absorbing material filled in the second cavity absorbs mid-to-high-frequency sound energy. The two are coupled to each other and complement each other in frequency band. According to actual measurements, in the frequency band of 50Hz~200Hz and under the condition of a frequency resolution of 1Hz, the transmission loss of the low-frequency noise reduction guide plate of this invention is not less than 12dB at each frequency point, and the minimum value reaches 18.1dB (located at the 185Hz frequency point), which breaks through the technical bottleneck of low noise reduction in the frequency band below 500Hz of existing resistive noise reduction guide plates.

[0021] (2) Adjustable silencing frequency. The low-frequency sound-absorbing module adopts a detachable installation method and has a variety of specifications. The resonant frequency of different specifications of modules is different. By selecting different specifications of modules for arrangement and / or adjusting the installation position of the modules in each first cavity, the silencing frequency characteristics of the guide plate can be changed, thereby achieving "on-demand frequency adjustment" for different target noise spectra, which is highly adaptable.

[0022] (3) Simple structure and high engineering value. The low-frequency sound absorption module is a modular molding structure. The resonant sound absorption structure can be formed by the perforated panel and the box body forming a resonant cavity. It does not require a complex metamaterial cell structure, has low manufacturing cost, and is easy to install and maintain. It is suitable for mass application in wind tunnel, ventilation and air conditioning and other engineering projects.

[0023] (4) Both airflow guidance and noise reduction functions are taken into account. The low-frequency sound-absorbing module and resistive sound-absorbing material are both built into the arc-shaped shell. The shape of the airflow guide is still designed according to the corner angle aerodynamic design. The airflow smoothly turns along the surface of the shell. The setting of the noise reduction structure does not affect the airflow guidance performance. Attached Figure Description

[0024] Figure 1 A schematic diagram of the structure of a sound-absorbing guide vane in the prior art;

[0025] Figure 2 A schematic cross-sectional view of the low-frequency noise-absorbing guide plate provided in an embodiment of the present invention;

[0026] Figure 3 A schematic diagram of the panel opening forms of eight specifications of low-frequency sound-absorbing modules provided in the embodiments of the present invention;

[0027] Figure 4 This is a schematic diagram of the installation structure of the low-frequency sound-absorbing module provided in an embodiment of the present invention;

[0028] Figure 5 The graph shows the transmission loss test results of the low-frequency noise-absorbing guide plate provided in the embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] like Figure 2 As shown, the low-frequency noise-absorbing guide vane in this embodiment includes an arc-shaped shell with an arc of 90°, which matches the angle of the wind tunnel corner. One end of the arc-shaped shell along the airflow direction is the leading edge, and the other end is the trailing edge. The leading edge is streamlined (in this embodiment, it is a circular arc transition) to reduce airflow resistance and prevent airflow separation. The wall surface of the arc-shaped shell on its outer arc surface is a rigid skin made of steel plate; the wall surface on its inner arc surface (i.e., the frontal side) is a perforated plate skin with a perforation diameter of 3mm and a perforation rate of 25%. In this way, sound waves outside the guide vane can only enter the interior of the shell through the perforated plate skin, while the rigid skin on the outer arc surface reflects and constrains the sound energy, so that the sound energy entering the shell is fully dissipated within the cavity.

[0031] The arc-shaped shell is divided into multiple independent cavities along its arc length by multiple partitions. In this embodiment, there are nine cavities, numbered sequentially from the leading edge to the trailing edge as cavity 1 to cavity 9; cavities 1 to 5 are the first cavities, each containing a low-frequency sound-absorbing module; cavities 6 to 9 are the second cavities, each filled with resistive sound-absorbing material, which is glass wool with a density of 32 kg / m³, used to absorb mid-to-high frequency sound energy and supplement low-frequency resonant sound absorption.

[0032] like Figure 3 As shown, the first type of low-frequency sound-absorbing module includes a housing. The wall of the housing facing the perforated plate skin is a panel with through holes. The remaining walls of the housing are closed, and the panel and the housing form a sealed resonant cavity. The through holes and the resonant cavity behind them constitute a resonant sound-absorbing structure (Helmholtz resonant sound-absorbing structure): when the frequency of the incident sound wave is close to the resonant frequency of this structure, the air column inside the through holes vibrates violently, rubbing against the hole walls and converting sound energy into heat energy, thereby achieving strong absorption of specific low-frequency sound waves. The resonant frequency is determined by the opening parameters of the through holes (number of openings, hole diameter, opening position, perforation rate) and the volume of the resonant cavity.

[0033] The second type of low-frequency sound-absorbing module, based on the first type of structure, has a resistive sound-absorbing layer (50mm thick glass wool in this embodiment) attached to the inner wall of the resonant cavity. A protective plate is placed on the side of the resistive sound-absorbing layer facing the resonant cavity. The protective plate is a perforated plate (30% perforation rate, 5mm aperture) used to fix and protect the resistive sound-absorbing layer, preventing it from scattering under airflow. The introduction of the resistive sound-absorbing layer increases the acoustic impedance of the resonant system, which can broaden the sound absorption bandwidth while maintaining the resonant sound absorption peak, so that the module has a high sound absorption capacity in a frequency band near the resonant frequency.

[0034] This embodiment provides eight specifications of low-frequency sound-absorbing modules, referred to as Module A to Module H (i.e., the first specification module to the eighth specification module), and their panel openings are as follows. Figure 3 As shown in Table 1, the structural parameters are as follows. The number of openings, diameter, position and perforation rate of the through holes 311 of the eight specifications of modules are different, as are the volumes of the resonant cavities 33, and therefore they have different resonant frequencies, with their sound absorption peaks distributed in the frequency range of 50Hz to 200Hz.

[0035] Table 1. Structural parameters of eight specifications of low-frequency sound-absorbing modules

[0036] Module A (First Specification) The central area has 2×2 openings with a hole spacing of 36mm. 12mm 4 holes 193×393×533 Module B (Second Specification) An opening is made in the central area; an additional hole is added at the center of the four holes in module A. 12mm 5 holes 193×393×533 Module C (Third Specification) The central area has 2 rows of 4 holes with a hole spacing of 36mm. 12mm 8 holes 273×443×533 Module D (Fourth Specification) The central area has 4 columns x 6 rows of holes with a hole spacing of 36mm. 12mm 24 holes 273×443×533 Module E (Fifth Specification) Perforation in the central area (120mm wide × 144mm high) 5mm 30% 273×443×533 Module F (Sixth Specification) Full-surface perforation of the panel 5mm 30% 273×443×533 Module G (Seventh Specification) The panel ends have a perforated section (210mm long), the rest are rigid sections. 3mm 25% 813×503×533 Module H (Eighth Specification) The panel has a perforated section (320mm long) in the middle, and the rest are rigid sections. 3mm 25% 813×423×533

[0037] In module E, the inner wall of the panel is lined with 50mm thick glass wool; the inner walls of the resonant cavities of modules F, G, and H are also lined with 50mm thick glass wool and covered with perforated protective plates (30% perforation rate, 5mm aperture). The panels of modules G and H each include perforated sections and rigid sections. The through holes in the perforated sections and the resonant cavities form a Helmholtz resonant sound-absorbing structure, while the box-like portion corresponding to the rigid section and the expansion space within the first cavity form an expansion cavity sound-absorbing structure. This utilizes the reflection and interference of sound waves at abrupt changes in the cross-section to further dissipate low-frequency sound energy.

[0038] like Figure 4 As shown, in this embodiment, the low-frequency sound-absorbing modules are arranged sequentially from the leading edge of the guide vane as follows: one module A, one module B, one module C, one module D, and one module E, followed by three modules F, and then one module G and one module H. The 6th to 9th cavities (the second cavity) are filled with glass wool with a density of 32 kg / m³. The small-volume, low-pore-count modules (module A and module B) are arranged close to the leading edge 13, while the large-volume modules (module G and module H) are arranged in the middle of the guide vane. The sound absorption peaks of each module are sequentially connected in the 50 Hz to 200 Hz frequency band, forming continuous coverage of the target frequency band.

[0039] An installation frame is provided inside the arc-shaped housing. The installation frame includes a protective panel installation frame set along both side walls of the housing and an angle steel installation frame fixed between adjacent modules. The edge of the low-frequency sound-absorbing module overlaps the installation frame and is detachably connected to the installation frame by fasteners (screws in this embodiment). When it is necessary to adjust the silencing frequency characteristics, simply loosen the fasteners to remove the corresponding module and replace it with a module of other specifications, or change the installation position of the module in each first cavity. The operation is simple.

[0040] When the low-frequency noise-absorbing guide plate of this invention is working, the airflow smoothly turns along the surface of the arc-shaped shell; noise waves enter the interior of the shell through the perforated plate skin on one side of the inner arc surface. For mid-to-high frequency sound waves, the resistive sound-absorbing material filled in the second cavity and the resistive sound-absorbing layer in each module dissipates them through viscous friction and heat exchange; for low-frequency sound waves of 50Hz~200Hz, the "through-hole-resonance cavity" structure of each low-frequency sound-absorbing module resonates at its respective resonant frequency, concentrating and dissipating the low-frequency sound energy. Since the resonant frequencies of the eight specifications of modules are different and are distributed at different frequencies within the target frequency band, multiple resonant sound absorption peaks couple and superimpose with each other, and are combined with the resistive noise reduction effect of the expansion cavity sound absorption structure, so that the guide plate obtains high transmission loss at each frequency point (frequency resolution 1Hz) in the entire 50Hz~200Hz frequency band, overcoming the defects of existing resistive guide plates that can only be tested at octave bands and have low low-frequency noise reduction.

[0041] This invention is the first to couple three resistive sound absorption mechanisms—perforated resonant sound absorption structure, Helmholtz resonant sound absorption structure, and expansion cavity sound absorption structure—and integrate them with the resistive sound absorption structure inside the corner guide plate, achieving low-frequency wideband high-efficiency noise reduction within the limited space of the guide plate.

[0042] The low-frequency noise-absorbing guide vane test piece was fabricated according to the above structure: the arc of the arc-shaped shell is 90°; the first to fifth cavities are constructed as follows: Figure 4 Install modules A through H in the order shown (with three modules F); fill cavities 6 through 9 with 32 kg / m³ glass wool; the perforated plate skin has a pore diameter of 3 mm and a perforation rate of 25%.

[0043] The transmission loss of the test piece was tested in the frequency band of 50Hz to 200Hz with a frequency resolution of 1Hz. The test results are as follows. Figure 5 As shown. Test results show that at all 151 frequency points within the 50Hz~200Hz frequency band, the transmission loss of the test piece is not lower than the design target value of 12dB; the minimum transmission loss occurs at the 185Hz frequency point, with a minimum value of 18.1dB, which is much higher than the design target value, and the transmission loss at most frequency points is between 25dB and 39dB. Compared with the existing resistive noise-absorbing guide plate, which has low noise reduction in the frequency band below 500Hz, the low-frequency noise reduction performance of this invention is significantly improved.

[0044] When the spectrum of the target noise changes, it is not necessary to replace the entire guide vane. Only the following adjustment steps are required: Based on the target noise reduction frequency, select a module with the corresponding resonant frequency from various specifications of low-frequency sound-absorbing modules 3 (modules A through H), loosen the fasteners at the corresponding positions, and install the selected module into the first cavity; and / or, swap the installation positions of modules of different specifications within each first cavity. Since the resonant frequency of a module is determined by its own structural parameters, and the installation position of the module affects the acoustic coupling relationship between modules, the transmission loss at each frequency point can be redistributed through the above replacement and position adjustment, achieving flexible adjustment of the noise reduction frequency characteristics.

[0045] Multiple low-frequency noise-absorbing guide vanes are arranged side-by-side at the corners of wind tunnels or bends in ventilation ducts, forming airflow channels between adjacent vanes, thus constituting a flow-guiding noise-absorbing device. Airflow smoothly changes direction through these channels, and noise waves are absorbed and dissipated frequency-by-frequency within each guide vane, thereby achieving low-frequency broadband noise reduction without affecting aerodynamic performance.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For example, the number of cavities can be set to other numbers according to the size of the guide vane; the ratio of the number of first cavities to second cavities, the specifications and structural parameters of the low-frequency sound-absorbing modules can be expanded according to the target frequency band; the resistive sound-absorbing material can also be other porous sound-absorbing materials such as rock wool; the curvature of the guide vane can also be other corner angles such as 97°. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-frequency noise-absorbing guide plate, comprising an arc-shaped shell, the arc-shaped shell having a rigid skin on one side of its outer arc surface and a perforated plate skin on one side of its inner arc surface, characterized in that, The arc-shaped shell is divided into multiple independent cavities along its arc length by multiple partitions. The multiple cavities include at least one first cavity and at least one second cavity. A low-frequency sound-absorbing module is provided in the first cavity. The low-frequency sound-absorbing module includes a housing. A through hole is opened on the panel of the housing facing the perforated plate skin. The panel and the housing form a closed resonant cavity. The through hole and the resonant cavity constitute a resonant sound-absorbing structure. Sound waves can enter the resonant cavity through the perforated plate skin and the through hole. The second cavity is filled with resistive sound-absorbing material.

2. The low-frequency noise-absorbing guide plate according to claim 1, characterized in that, The low-frequency sound-absorbing module is detachably installed in the first cavity; the low-frequency sound-absorbing module includes various specifications, and the low-frequency sound-absorbing modules of different specifications have different numbers of openings, opening diameters, opening positions and perforation rates of the through holes, and / or different volumes of the resonant cavity, so that the low-frequency sound-absorbing modules of different specifications have different resonant frequencies.

3. The low-frequency noise-absorbing guide plate according to claim 2, characterized in that, There are multiple first cavities, which are arranged along the arc length of the arc-shaped shell, and the low-frequency sound-absorbing modules installed in at least two of the first cavities have different specifications.

4. The low-frequency noise-absorbing guide plate according to claim 2 or 3, characterized in that, An installation frame is provided inside the arc-shaped housing, and the low-frequency sound-absorbing module is detachably connected to the installation frame via fasteners.

5. The low-frequency noise-absorbing guide plate according to any one of claims 1 to 3, characterized in that, The panel includes a perforated section and a rigid section, and the through hole is formed in the perforated section; the through hole on the perforated section and the resonant cavity form a Helmholtz resonant sound absorption structure, and the rigid section and the expansion space in the first cavity form an expansion cavity sound absorption structure.

6. The low-frequency noise-absorbing guide plate according to any one of claims 1 to 3, characterized in that, The inner wall of the resonant cavity is attached with a resistive sound-absorbing layer, and a protective plate is provided on the side of the resistive sound-absorbing layer facing the resonant cavity. The protective plate is a perforated plate.

7. The low-frequency noise-absorbing guide plate according to any one of claims 1 to 3, characterized in that, There are nine cavities, numbered sequentially from the front edge to the rear edge of the arc-shaped shell as cavity 1 to cavity 9, wherein cavity 1 to cavity 5 are the first cavities, and cavity 6 to cavity 9 are the second cavities.

8. The low-frequency noise-absorbing guide plate according to claim 8, characterized in that, The first cavity contains a first specification module, a second specification module, a third specification module, a fourth specification module, and a fifth specification module arranged sequentially from the leading edge side. The first cavity also contains at least one of a sixth specification module, a seventh specification module, and an eighth specification module.

9. A flow-guiding and noise-reducing device, characterized in that, It includes multiple low-frequency noise-absorbing guide vanes arranged side by side as described in any one of claims 1 to 9, with an airflow channel formed between two adjacent low-frequency noise-absorbing guide vanes.

10. A method for adjusting the silencing frequency of a low-frequency silencing guide vane, characterized in that, The implementation based on the low-frequency sound-absorbing guide plate as described in any one of claims 1 to 8 includes: selecting a low-frequency sound-absorbing module with a corresponding resonant frequency from a variety of low-frequency sound-absorbing modules according to the target sound-absorbing frequency, and installing the selected low-frequency sound-absorbing module in the first cavity; and / or adjusting the installation position of the low-frequency sound-absorbing module in the plurality of first cavities to adjust the transmission loss of the low-frequency sound-absorbing guide plate at each frequency point.

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