Frequency-adjustable multi-layer structure medium and low frequency silencer and application thereof

Abstract

The invention discloses a frequency-adjustable multi-layer structure medium and low frequency silencer and application thereof.The silencer comprises a Helmholtz cavity layer, an MPP layer and a PM layer which are sequentially and coaxially arranged from left to right, the MPP layer and the PM layer are installed in a right pipe body of a first pipe body, and the MPP layer abuts against a separation ring in the first pipe body; the small-diameter section of the second pipe body is inserted into the left pipe body of the first pipe body in a sliding manner; the Helmholtz cavity layer is mounted in the large-diameter section of the second pipe body; when the second pipe body slides relative to the first pipe body, the thickness of the air cavity between the Helmholtz cavity layer and the MPP layer is changed accordingly, and then the frequency of the silencer can be changed. The silencer can achieve a good low and medium frequency sound wave absorption effect, and can be used as an anechoic tile on the surface of a submarine, an anechoic wall in a building, an anechoic cover above an automobile engine and the like.

Description

Technical Field

[0001] The invention relates to a muffler, in particular to a frequency-adjustable multi-layer structure medium and low frequency muffler and application thereof. Background Art

[0002] CN109379670A proposes a thin film type Helmholtz silencer, in which multiple Helmholtz cavities are arranged, and the sound absorption frequency is adjusted by a thin film in the middle, so that sound waves with a frequency below 500Hz can be absorbed. However, the sound absorption frequency range is too narrow, and the sound absorption effect for medium and low frequency (above 500Hz) sound waves is poor. Taking the solution of four Helmholtz cavities as an example, Figure 1 From the simulation curve, it can be seen that the sound absorption coefficient reaches 0.95 at around 400Hz. As the frequency increases, the sound absorption coefficient drops sharply, and the sound absorption coefficient at medium and low frequencies is lower than 0.3. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a frequency-adjustable multi-layer low-frequency muffler and its application.

[0004] Technical solution: The present invention discloses a frequency-adjustable multi-layer low-frequency muffler, comprising a Helmholtz cavity layer, an MPP layer and a PM layer coaxially arranged from left to right, wherein an air cavity with adjustable thickness is provided between the Helmholtz cavity layer and the MPP layer.

[0005] Furthermore, the frequency-adjustable multi-layer structure medium and low frequency muffler also includes a first tube body and a second tube body, wherein the first tube body has a circle of separating rings inside, separating the first tube body into a left tube body and a right tube body, and the MPP layer and the PM layer are installed in the right tube body, wherein the MPP layer abuts against the separating ring; the second tube body has a large diameter section and a small diameter section, wherein the small diameter section is slidably inserted in the left tube body of the first tube body, and the Helmholtz cavity layer is installed in the large diameter section of the second tube body; when the second tube body slides relative to the first tube body, the thickness of the air cavity between the Helmholtz cavity layer and the MPP layer changes accordingly.

[0006] Furthermore, the upper limit of the thickness of the air cavity is 50 mm, and the lower limit is determined by the length of the left tube body of the first tube body and the length of the small diameter section of the second tube body.

[0007] Furthermore, the frequency-adjustable multi-layer low-frequency muffler also includes a left cover plate and a right cover plate, wherein the left cover plate is used to fix the Helmholtz cavity layer in the second tube body, and the right cover plate is used to fix the MPP layer and the PM layer in the first tube body.

[0008] Furthermore, the length of the low frequency muffler in the entire multi-layer structure is 71 to 121 mm.

[0009] Furthermore, each of the Helmholtz cavity layer, the MPP layer and the PM layer is provided with a circle of acoustic wall on its periphery for preventing the transmission of sound waves.

[0010] Furthermore, the Helmholtz cavity layer is made of Somos glass reinforced polyester (GP) Plus material, whose Young's modulus E is 4.35×10^9Pa, Poisson's ratio ν is 0.38, and mass density ρ is 1180kg / m 3 .

[0011] Further,

[0012] Perforation rate Thickness(mm) Cavity thickness (mm) Radius(mm) 1％ 1 10 0.5

[0013] The material of the MPP layer is aluminum plate, and its physical parameters are shown in the table above.

[0014] Further,

[0015] Porosity <![CDATA[Flow resistance ratio N·s / m 4 > Tortuosity Factor 0.95 15000 1.24 Viscous characteristic length (μm) Thermal characteristic length (μm) Thickness(mm) 105 140 50

[0016] The PM layer material is the Johnson-Champoux-Allard model, and its physical parameters are shown in the table above.

[0017] The frequency-adjustable multi-layer structure low-frequency muffler is used as a submarine surface muffler tile, a building muffler wall or a muffler cover above a car engine.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: In order to solve the defect that the Helmholtz cavity has a narrow sound absorption band and cannot absorb medium and low frequencies, the present invention adds an MPP layer and a PM layer on the basis of the existing Helmholtz resonance cavity sound absorber to form a multi-layer structure muffler, which achieves good medium and low frequency sound absorption effect. The thickness of the air cavity between the Helmholtz cavity layer and the MPP layer is adjustable, which can adjust the muffler to the frequency corresponding to the maximum sound absorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a simulation curve diagram of the existing film-type Helmholtz muffler;

[0020] Figure 2 It is a structural schematic diagram of a frequency-adjustable multi-layer low-frequency muffler provided by an embodiment of the present invention;

[0021] Figure 3 yes Figure 2 Assembly drawing of

[0022] Figure 4 This is a simulation comparison diagram of a multi-layer structure muffler and a single-layer structure muffler;

[0023] Figure 5This is a comparison chart of simulation and experimental data of multi-layer structure muffler;

[0024] Figure 6 This is a simulation comparison diagram of different air cavity thicknesses of multi-layer structure muffler;

[0025] Figure 1 and Figures 4 to 6 In the figure, the horizontal axis represents frequency and the vertical axis represents the absorption coefficient. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings.

[0027] Attached Figures 1 to 6 The reference numerals in the figures are as follows:

[0028] 1, Helmholtz cavity layer; 2, acoustic wall; 3, MPP layer; 4, PM layer; 5, first tube body; 6, second tube body; 7, left cover plate; 8, right cover plate.

[0029] like Figure 2 and Figure 3 As shown, an embodiment of the present invention provides a frequency-adjustable multi-layer structure medium and low frequency muffler, including a Helmholtz cavity layer 1, an MPP (microperforated plate) layer 3, a PM (porous material) layer 4, a first tube body 5, a second tube body 6, a left cover plate 7 and a right cover plate 8. The first tube body 5 has a circle of separating rings inside, which separates the first tube body 5 into a left tube body and a right tube body.

[0030] The MPP layer 3 and the PM layer 4 are installed in the right tube body, wherein the MPP layer 3 is against the separation ring. The second tube body 6 has a large diameter section and a small diameter section, wherein the small diameter section is slidably inserted into the left tube body of the first tube body 5, and the Helmholtz cavity layer 1 is installed in the large diameter section of the second tube body 6, and the Helmholtz cavity layer 1, the MPP layer 3 and the PM layer 4 are coaxial. In addition, the periphery of the Helmholtz cavity layer 1, the MPP layer 3 and the PM layer 4 are each provided with a circle of acoustic wall 2, which plays a role in preventing the transmission of sound waves during simulation.

[0031] An air cavity is formed between the Helmholtz cavity layer 1 and the MPP layer 3. When the second tube body 6 slides relative to the first tube body 5, the thickness of the air cavity changes accordingly. Changing the thickness of the air cavity is equivalent to changing the size of the cavity inside the microperforated plate. The cavity inside the microperforated plate is related to the sound-absorbing frequency of the microperforated plate. Therefore, adjusting the thickness of the air cavity can change the frequency of the muffler.

[0032] The left cover plate 7 is used to fix the Helmholtz cavity layer 1 in the second tube body 6, and the right cover plate 8 is used to fix the MPP layer 3 and the PM layer 4 in the first tube body 5. In this embodiment, the cover plate and the tube body are bonded by glue.

[0033] In this embodiment, the upper limit of the thickness of the air cavity is 50 mm, and the lower limit is determined by the length of the left tube body of the first tube body 5 and the length of the small diameter section of the second tube body 6. The length of the low-frequency muffler in the entire multi-layer structure is 71 to 121 mm. The low-frequency muffler in the multi-layer structure can be used as a muffler tile on the surface of a submarine, because the thickness of the muffler tile is usually no more than 150 mm, and the multi-layer structure can perfectly meet this requirement. In addition, the low-frequency muffler in the multi-layer structure can also be applied to many civilian fields, such as muffler walls in cinemas and other buildings, muffler covers above car engines, etc.

[0034] The overall length of the low-frequency muffler in the multi-layer structure can be further reduced to meet more demanding usage requirements. For example, the perforation rate of the micro-perforated plate can be changed to reduce the thickness of the air cavity, and the geometric parameters of the porous material can be changed to reduce its thickness.

[0035] The Helmholtz cavity layer 1 adopts the structure given in CN109379670A, with unit cell length l1=5mm, l2=20mm, l3=10mm, overall radius R=30mm, pipe radius a=20mm, partition thickness t=2mm, pipe thickness 2t=4mm, neck radius r=1mm, and neck length l=5mm. The Helmholtz cavity layer 1 is made of Somos glass reinforced polyester (GP) Plus material, with a Young's modulus E of 4.35×10^9Pa, a Poisson's ratio ν of 0.38, and a mass density ρ of 1180kg / m 3 .

[0036] The material of MPP (micro perforated plate) layer 3 is aluminum plate, and its physical parameters are shown in Table 1.

[0037] Table 1

[0038] Perforation rate Thickness(mm) Cavity thickness (mm) Radius(mm) 1％ 1 10 0.5

[0039] The material of PM (porous material) layer 4 is Johnson-Champoux-Allard model, and its physical parameters are shown in Table 2.

[0040] Table 2

[0041] Porosity <![CDATA[Flow resistance ratio N·s / m 4 > Tortuosity Factor 0.95 15000 1.24 Viscous characteristic length (μm) Thermal characteristic length (μm) Thickness(mm) 105 140 50

[0042] The working principle of the low-frequency muffler in the multi-layer structure described in the embodiment of the present invention is as follows.

[0043] In this multilayer structure, both the Helmholtz cavity layer and the microperforated plate (MPP) layer can be regarded as a Helmholtz resonant cavity. The former localizes the wave in the longitudinal direction, and the latter localizes the wave in the axial direction. Since the neck volume of the Helmholtz resonant cavity is much smaller than the volume of the cavity, it can be approximately considered that the fluid in the neck is incompressible. However, under the action of the neck fluid movement, the fluid in the cavity is considered compressible. The fluid in the cavity will naturally increase in pressure after being compressed, thereby generating a reverse restoring force.

[0044] According to the above description, the fluid in the neck can be regarded as a mass block, and the fluid in the cavity can be regarded as a spring. When the excitation frequency is close to the characteristic frequency of the resonant cavity, the Helmholtz cavity has the ability to absorb sound waves. Therefore, we can obtain very low sound absorption frequencies by designing appropriate geometric shapes and physical materials. The main physical mechanism of noise reduction in porous material (PM) structures is that there are a large number of irregular and interconnected pores or gaps in porous sound-absorbing structures. When sound waves enter the interior through pores or gaps, part of the sound waves are reflected on the surface, while the other part enters the holes or gaps. Due to the friction between the air and the holes, the sound waves will continuously consume energy when propagating in the micropores or gaps, which makes the structure have a sound-absorbing effect. Therefore, the PM layer has a wider sound absorption frequency range in the medium and high frequency bands.

[0045] Figure 4 The experimental results of single-layer and multi-layer structures are shown. It can be seen that at extremely low frequencies (400 Hz), the sound absorption coefficient of the multi-layer structure is greater than that of the single-layer structure. This is because the Helmholtz resonant cavity can significantly reduce noise in the low-frequency band, which has also been verified in theory and simulation. Figure 5 The comparison between the experimental and simulation results is shown, and the results show a high degree of agreement between the two. However, at frequencies above 1000 Hz, the experimental sound absorption coefficient is slightly lower than the simulation result. This is mainly due to the fact that the airtightness of the device is not ideal, resulting in some plane waves passing through the gaps without being absorbed. In summary, the corresponding experimental results confirm that the multilayer structure can not only show a high sound absorption coefficient in a wide frequency range of 400 to 1600 Hz (the average sound absorption coefficient reaches 0.9), but also show excellent performance at extremely low frequencies (400 Hz).

[0046] We also conducted another experiment, that is, changing the thickness of the air cavity between the Helmholtz cavity layer and the MPP layer while keeping other structural parameters unchanged. The experimental results were sorted out using MATLAB software and compared with the simulation results, such as Figure 6As shown. It can be seen that below 1000Hz, with the increase of the thickness of the air cavity, the sound absorption coefficient increases significantly. When the thickness is 50mm, the sound absorption performance is the best. However, above 1000Hz, the 50mm thick air cavity causes a slight decrease in the sound absorption coefficient. Despite the decrease, the sound absorption coefficient remains above 0.9 at frequencies above 1000Hz. In contrast, the structure with an air cavity thickness of 25mm has better sound absorption at frequencies above 1000Hz. In the frequency range of 1100 to 1300Hz, the sound absorption coefficient is almost close to 1, so the sound waves in this frequency band can be completely absorbed. This experimental result shows that different air cavity thicknesses can be selected to meet different frequency requirements. For low frequencies, a larger cavity thickness can be selected; for medium and high frequencies, a medium cavity thickness can be selected.

Claims

1. A frequency-adjustable multi-layer low-frequency muffler, characterized in that: The invention comprises a Helmholtz cavity layer (1), an MPP layer (3) and a PM layer (4) which are coaxially arranged in sequence from left to right, wherein an air cavity with adjustable thickness is provided between the Helmholtz cavity layer (1) and the MPP layer (3).

2. The frequency-adjustable multi-layer low-frequency muffler according to claim 1 is characterized in that: The invention also comprises a first tube body (5) and a second tube body (6), wherein the first tube body (5) has a circle of dividing rings inside to divide the first tube body (5) into a left tube body and a right tube body, and the MPP layer (3) and the PM layer (4) are installed in the right tube body, wherein the MPP layer (3) abuts against the dividing ring; the second tube body (6) has a large diameter section and a small diameter section, wherein the small diameter section is slidably inserted in the left tube body of the first tube body (5), and the Helmholtz cavity layer (1) is installed in the large diameter section of the second tube body (6); when the second tube body (6) slides relative to the first tube body (5), the thickness of the air cavity between the Helmholtz cavity layer (1) and the MPP layer (3) changes accordingly.

3. The frequency-adjustable multi-layer low-frequency muffler according to claim 2 is characterized in that: The upper limit of the thickness of the air cavity is 50 mm, and the lower limit is determined by the length of the left tube body of the first tube body (5) and the length of the small diameter section of the second tube body (6).

4. The frequency-adjustable multi-layer low-frequency muffler according to claim 3 is characterized in that: It also includes a left cover plate (7) and a right cover plate (8), wherein the left cover plate (7) is used to fix the Helmholtz cavity layer (1) in the second tube body (6), and the right cover plate (8) is used to fix the MPP layer (3) and the PM layer (4) in the first tube body (5).

5. The frequency-adjustable multi-layer low-frequency muffler according to claim 4 is characterized in that: The length of the low-frequency silencer in the entire multi-layer structure is 71 to 121 mm.

6. The frequency-adjustable multi-layer low-frequency muffler according to claim 1, characterized in that: The Helmholtz cavity layer (1), the MPP layer (3) and the PM layer (4) are each provided with a circle of acoustic wall (2) on the periphery thereof for preventing the transmission of sound waves.

7. The frequency-adjustable multi-layer low-frequency muffler according to claim 1, characterized in that: The Helmholtz cavity layer (1) is made of Somos glass reinforced polyester (GP) Plus material, with a Young's modulus E of 4.35×10^9 Pa, a Poisson's ratio ν of 0.38, and a mass density ρ of 1180 kg / m3.

8. The frequency-adjustable multi-layer low-frequency muffler according to claim 1, characterized in that: The material of the MPP layer (3) is an aluminum plate, and its physical parameters are shown in the above table.

9. The frequency-adjustable multi-layer low-frequency muffler according to claim 1, characterized in that: The material of the PM layer (4) is the Johnson-Champoux-Allard model, and its physical parameters are shown in the table above.

10. Use of the frequency-adjustable multi-layer low-frequency muffler according to claim 1 as a submarine surface muffler tile, a building muffler wall, or a muffler cover above a car engine.

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