Low-frequency sound absorption device for wind tunnel corner flow deflector

Abstract

The invention discloses a low-frequency sound absorption device for a wind tunnel corner flow deflector, and the device comprises a housing which is internally provided with a low-frequency sound absorber and an impedance matching layer. The low-frequency sound absorber comprises a Helmholtz resonance cavity, a sealing ring and an elastic support, the Helmholtz resonance cavity is distributed in the sealing ring in a square lattice or rectangular lattice mode, and the sealing ring is connected with the shell through the elastic support; the impedance matching layer comprises a porous material layer, an air matching layer and a gradual change section cavity, the porous material layer is connected with the surface, closest to sound wave incidence, of the shell, the air matching layer is located between the porous material layer and the gradual change section cavity, and the sectional area of the gradual change section cavity is gradually increased in the sound wave incidence direction. The thickness of the low-frequency sound absorption device does not exceed 650 mm, the low-frequency sound absorption device is high in aerodynamic noise absorption coefficient at the low frequency band of 50-200 Hz, has excellent high-temperature resistance, can stably operate in the working environment of 150 DEG C or above, and meets the strict working conditions of a wind tunnel laboratory.

Description

Technical Field

[0001] The invention belongs to a low-frequency sound absorbing device, in particular to a low-frequency sound absorbing device used for a wind tunnel corner guide vane. Background Art

[0002] As the requirements for wind tunnel noise control in the aerospace and low-altitude economy sectors continue to increase, existing sound-absorbing materials and noise-reducing structures face a series of technical challenges. Traditional porous materials perform poorly in the low-frequency range (<200Hz), with sound absorption coefficients generally below 0.3. To achieve a certain sound absorption effect, traditional materials typically require a large thickness (>600mm), which conflicts with the requirements for the structure and lightweight design of the deflector. Furthermore, while the Helmholtz cavity resonator can achieve efficient sound absorption in a specific frequency range, its large cavity space requirement severely disrupts the aerodynamic shape of the deflector, leading to flow field instability and compromising the accuracy of experimental results. Attempts to expand the sound absorption band through the use of impedance gradient structures still cannot avoid the turbulent effects in the low-frequency range, resulting in a significant shift in the sound absorption band between 50-200Hz, with the sound absorption peak deviation reaching up to ±15%, seriously affecting the overall sound reduction effect.

[0003] Given this, there is an urgent need to develop a highly efficient, low-frequency sound absorption module that does not affect the wind tunnel flow field. In particular, in the 50-200Hz frequency range, improving the guide vane's aerodynamic noise absorption coefficient (target ≥ 0.90) while ensuring a structural thickness of no more than 650mm presents a key technical challenge. Furthermore, the sound-absorbing materials and structures employed must exhibit excellent high-temperature resistance, capable of stable operation in operating environments exceeding 150°C, thus meeting the rigorous working conditions of the wind tunnel laboratory. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a low-frequency sound absorbing device for wind tunnel corner guide vanes with good low-frequency noise suppression effect.

[0005] Technical solution: The low-frequency sound absorption device for a wind tunnel corner guide vane described in the present invention includes a shell, in which a low-frequency sound absorber and an impedance matching layer are arranged; the low-frequency sound absorber includes a Helmholtz resonance cavity, a sealing ring, and an elastic bracket. The Helmholtz resonance cavity is distributed in the form of a square lattice or a rectangular lattice in the sealing ring. The sealing ring is connected to the shell through an elastic bracket, which is beneficial to reducing the influence of low-frequency failure of sound absorption performance caused by thin-wall vibration generated by the action of high-speed airflow on the surface of the Helmholtz resonance cavity; the impedance matching layer includes a porous material layer, an air matching layer, and a gradient cross-section cavity. The porous material layer is connected to the surface of the shell closest to the sound wave incident, and the air matching layer is located between the porous material layer and the gradient cross-section cavity, mainly used to reduce the influence of surface acoustic impedance mutation when the sound wave propagates in different media. The cross-sectional area of ​​the gradient cross-section cavity gradually increases along the direction of sound wave incidence.

[0006] Furthermore, the shell includes an outer shell, a perforated protective panel, a fiber sound-absorbing cloth and a damping layer. The outer shell and the perforated protective panel are enclosed as a whole. The fiber sound-absorbing cloth is arranged between the perforated protective panel and the porous material layer, and the damping layer is arranged between the outer shell and the low-frequency sound absorber.

[0007] Furthermore, the perforated protective plate is an aluminum or galvanized steel perforated plate with a perforation rate of 15% to 30% and a thickness of 0.5 to 1.5 mm. Preferably, the perforation rate is 18% and the thickness is 1.0 mm.

[0008] Furthermore, the fiber sound-absorbing fabric is a sound-absorbing non-woven fabric with a thickness of 0.1 to 0.5 mm. Preferably, the thickness is 0.3 mm. The fiber sound-absorbing fabric helps reduce the effects of wind speed and small impurities such as dust on the sound absorption performance of the porous material layer and the low-frequency sound absorber.

[0009] Furthermore, the damping layer is a phononic crystal sandwich structure, including a top layer, a phononic crystal, and a bottom layer. The phononic crystals are cylindrically periodically distributed, with a thickness of 1 to 3 mm, and the thickness of the top and bottom layers is 0.5 to 1.5 mm. Preferably, the thickness of the phononic crystals is 2 mm, and the thickness of the top and bottom layers is 1 mm.

[0010] Furthermore, the outer shell is a box body formed by bending and welding aluminum plates or galvanized steel plates, with a side length of 200-400 mm and a thickness of 0.5-1.5 mm. Preferably, the side length is 300 mm and the thickness is 1.0 mm.

[0011] Furthermore, the height of the low-frequency sound absorber is 350-600 mm, and the low-frequency sound absorber further comprises a low-frequency resonance cavity, which is arranged on a side of the Helmholtz resonance cavity away from the tapered cross-section cavity.

[0012] Furthermore, the number of the Helmholtz resonance cavities is 50 to 100, and the cross-sectional shape is a quadrilateral with a side length of 196 to 388 mm and a thickness of 250 to 450 mm. Preferably, the side length is 292 mm and the thickness is 400 mm.

[0013] Furthermore, the thickness of the air matching layer is 5-10 mm, and the thickness of the gradient cross-section cavity is 10-44 mm.

[0014] Furthermore, the gradually varying cross-section cavity is a trapezoidal cross-section cavity, and the bottom angle of the trapezoidal cross-section cavity is 5 to 30 degrees. The trapezoidal cross-section cavity can further reduce the wind speed and reduce its impact on the sound absorption performance of the porous material layer and the low-frequency sound absorber.

[0015] Working Principle: When aerodynamic noise is incident tangentially on the surface of the low-frequency sound absorption module, the aperture of the perforated cover plate causes the aerodynamic noise to enter the module's interior. The porous material layer, air matching layer, and tapered cross-section cavity within the impedance matching layer work together to reduce the velocity of aerodynamic noise propagating through the module, significantly minimizing the impact of airflow on the low-frequency sound absorption performance. When low-velocity noise is incident perpendicularly on the surface of the low-frequency sound absorption module, local resonance causes the low-frequency noise to resonate within the series-parallel composite Helmholtz resonance cavity. Friction with the wall converts the acoustic energy into heat, dissipating the acoustic energy. A combination of a sealing ring and an elastic bracket minimizes the degradation of low-frequency sound absorption performance caused by deformation of the upper cover plate of the Helmholtz resonance cavity due to low-frequency noise. By adjusting the thickness of the low-frequency resonance cavity, the sound absorption performance of the low-frequency sound absorption module in the 50-200Hz frequency range is improved. Finally, due to the shearing effect of the phononic crystals in the damping layer, the low-frequency sound absorption module is further improved in suppressing low-frequency noise below 100 Hz.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0017] 1. The thickness of the low-frequency sound absorption device does not exceed 650mm. In the low-frequency band of 50-200Hz, it has a high sound absorption coefficient for aerodynamic noise and excellent high-temperature resistance. It can operate stably in working environments up to 150°C and above, meeting the rigorous working conditions of the wind tunnel laboratory.

[0018] 2. The structure is novel, compact and light. The sealing ring, elastic bracket and gradient cross-section cavity solve the low-frequency failure problem caused by resonant deformation.

[0019] 3. The shear deformation of the phononic crystal further improves the suppression effect of low-frequency noise;

[0020] 4. Low-frequency sound absorption performance is related to structural parameters. By adjusting the design parameters of the structure, its effective frequency band and acoustic performance can be changed. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 It is a front view of the present invention;

[0023] Figure 3 This is a cross-sectional view of the AA surface of the present invention;

[0024] Figure 4 This is a front view of the Helmholtz resonance chamber 21 of the present invention;

[0025] Figure 5 It is a BB-side cross-sectional view of the present invention;

[0026] Figure 6 is a three-dimensional diagram of the damping layer 14 of the present invention;

[0027] Figure 7 is a perspective view of the Helmholtz resonance chamber 21 of the present invention;

[0028] Figure 8 It is a left side view of the Helmholtz resonance chamber 21 of the present invention;

[0029] Figure 9 2 is a schematic structural diagram of the elastic bracket 23 of the present invention;

[0030] Figure 10 This is the acoustic impedance diagram of the present invention in the 50-200 Hz frequency band;

[0031] Figure 11 1 is a graph showing the sound absorption coefficient of the present invention. DETAILED DESCRIPTION

[0032] like Figure 1~Figure 2 The shell 1 of the low-frequency sound absorbing device for the wind tunnel corner guide vane contains a low-frequency sound absorbing body 2 and an impedance matching layer 3. The outer dimensions of the shell 1 are 300 mm (length) × 300 mm (width) × 475 mm (height).

[0033] like Figures 3 to 9The low-frequency sound absorber 2 comprises a Helmholtz resonance chamber 21 (based on polyphenylene sulfide (PPS)), a sealing ring 22 (made of hydrogenated nitrile butadiene rubber (HNBR)), an elastic bracket 23, and a low-frequency resonance chamber 24. There are 50 Helmholtz resonance chambers 21, each with a quadrilateral cross-section. They are spatially arranged in a series-parallel configuration, forming a square or rectangular lattice. Specifically, the Helmholtz resonance chambers 21 are arranged in a 5x5 array in the XY plane, with two layers arranged in series along the Z axis. The overall dimensions of the Helmholtz resonance chambers 21 are 292 mm (length) × 292 mm (width) × 400 mm (height). The sealing ring 22 and elastic bracket 23 are mounted within the Helmholtz resonance chambers 21, which are fixedly connected to the housing 1 via the elastic bracket 23. The low-frequency resonance chambers 24 are arranged in series with the Helmholtz resonance chambers 21, and their thickness (D) is 50 mm. The sound and energy absorption of the low-frequency sound absorbing body 2 can be improved by adjusting the thickness of the low-frequency resonance cavity 24 .

[0034] The shell 1 comprises an outer shell 11, a perforated protective panel 12, a fiber sound-absorbing fabric 13, and a damping layer 14. The outer shell 11 and the perforated protective panel 12 form an integral unit. The fiber sound-absorbing fabric 13 is disposed between the perforated protective panel 12 and the porous material layer 31. The damping layer 14 is disposed between the outer shell 11 and the low-frequency sound absorber 2. The perforated protective panel 12 is a perforated aluminum or galvanized steel plate with a perforation ratio of 15% to 30% and a thickness of 0.5 to 1.5 mm. The fiber sound-absorbing fabric 13 is a polyester non-woven fabric with a thickness of 0.1 to 0.5 mm. The damping layer 14 is an EPDM-based phononic crystal sandwich structure, comprising a top layer 141, a phononic crystal 142, and a bottom layer 143. The thicknesses L are 1.0 mm, 2.0 mm, and 1.0 mm, respectively. The phononic crystal 142 in the center of the structure is periodically distributed in a cylindrical shape. The low-frequency suppression capability of the low-frequency sound absorption module can be further improved by shear deformation of the phononic crystals 142 in the damping layer 14 .

[0035] Impedance matching layer 3 comprises a porous material layer 31 (centrifugal glass wool), an air matching layer 32, and a tapered cross-section cavity 33 (made of an aluminum substrate). These layers are arranged sequentially along the direction of acoustic wave incidence, with thicknesses D of 2.0 mm, 8.0 mm, and 15.0 mm, respectively. Tapered cross-section cavity 33 is a trapezoidal cavity with a thickness of 15.0 mm and a taper angle of 18.5°.

[0036] like Figure 10-11Experimental measurements were conducted on the aforementioned low-frequency sound absorption module (a rectangular impedance tube), yielding a graph of its acoustic impedance and sound absorption coefficient. With an overall structural thickness (H) of 475mm, the sound absorption coefficient of the low-frequency sound absorption module was greater than 0.90 at all frequencies (1Hz intervals) within the 50-200Hz frequency range, with the average sound absorption coefficient within this frequency range approaching 0.95. Furthermore, within the 50-200Hz frequency range, the real part of the acoustic impedance of the low-frequency sound absorption module ranged from 0.5 to 1.5, while the imaginary part ranged from -0.5 to 0.5, consistent with the sound absorption coefficient characteristics.

[0037] The low-frequency sound absorption device of this embodiment can be used in wind tunnel loop corner guide vanes, resolving the low-frequency failure issue of existing sound absorption modules at high flow rates. The low-frequency sound absorption module offers excellent low-frequency sound absorption performance, and its robust structure significantly enhances the low-frequency noise suppression capability of wind tunnel loop corner guide vanes.

Claims

1. A low-frequency sound absorption device for a wind tunnel corner guide vane, characterized by: The invention comprises a shell (1), wherein a low-frequency sound absorber (2) and an impedance matching layer (3) are arranged in the shell (1); the low-frequency sound absorber (2) comprises a Helmholtz resonance cavity (21), a sealing ring (22), and an elastic bracket (23); the Helmholtz resonance cavity (21) is distributed in the sealing ring (22) in the form of a square lattice or a rectangular lattice, and the sealing ring (22) is connected to the shell (1) through the elastic bracket (23); the impedance matching layer (3) comprises a porous material layer (31), an air matching layer (32), and a gradient cross-section cavity (33); the porous material layer (31) is connected to the surface of the shell (1) closest to the incident sound wave, the air matching layer (32) is located between the porous material layer (31) and the gradient cross-section cavity (33), and the cross-sectional area of ​​the gradient cross-section cavity (33) gradually increases along the direction of the incident sound wave.

2. A low-frequency sound absorbing device for a wind tunnel corner guide vane according to claim 1, characterized in that: The shell (1) comprises an outer shell (11), a perforated protective panel (12), a fiber sound-absorbing cloth (13) and a damping layer (14); the outer shell (11) and the perforated protective panel (12) are enclosed as a whole; the fiber sound-absorbing cloth (13) is arranged between the perforated protective panel (12) and the porous material layer (31); and the damping layer (14) is arranged between the outer shell (11) and the low-frequency sound absorber (2).

3. The low-frequency sound absorption device for a wind tunnel corner guide vane according to claim 2, characterized in that: The perforated protective panel (12) is an aluminum or galvanized steel perforated plate with a perforation rate of 15% to 30% and a thickness of 0.5 to 1.5 mm.

4. The low-frequency sound absorption device for a wind tunnel corner guide vane according to claim 2, characterized in that: The fiber sound-absorbing cloth (13) is a sound-absorbing non-woven fabric with a thickness of 0.1-0.5 mm.

5. The low-frequency sound absorption device for a wind tunnel corner guide vane according to claim 2, characterized in that: The damping layer (14) is a phononic crystal sandwich structure, comprising a top layer (141), a phononic crystal (142) and a bottom layer (143); the phononic crystal (142) is cylindrically periodically distributed and has a thickness of 1 to 3 mm; the thickness of the top layer (141) and the bottom layer (143) is 0.5 to 1.5 mm.

6. The low-frequency sound absorbing device for a wind tunnel corner guide vane according to claim 2, characterized in that: The outer shell (11) is a box body formed by bending and welding aluminum plates or galvanized steel plates, with a side length of 200-400 mm and a thickness of 0.5-1.5 mm.

7. The low-frequency sound absorption device for a wind tunnel corner guide vane according to claim 1, characterized in that: The low-frequency sound absorber (2) has a height of 350-600 mm. The low-frequency sound absorber (2) further comprises a low-frequency resonance cavity (24). The low-frequency resonance cavity (24) is arranged on a side of the Helmholtz resonance cavity (21) away from the tapered cross-section cavity (33).

8. The low-frequency sound absorption device for a wind tunnel corner guide vane according to claim 1, characterized in that: The number of the Helmholtz resonance cavities (21) is 50 to 100, and the cross-sectional shape is a quadrilateral with a side length of 196 to 388 mm and a thickness of 250 to 450 mm.

9. The low-frequency sound absorbing device for a wind tunnel corner guide vane according to claim 1, characterized in that: The thickness of the air matching layer (32) is 5-10 mm, and the thickness of the gradient cross-section cavity (33) is 10-44 mm.

10. The low-frequency sound absorption device for a wind tunnel corner guide vane according to claim 1, characterized in that: The gradually changing cross-section cavity (33) is a trapezoidal cross-section cavity.

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