Micro-perforated panel composite gradient spiral duct sound absorption device and method

Abstract

The present application belongs to the technical field of low-frequency sound absorption, and discloses a micro-perforated panel composite gradient spiral pipe sound absorption device and method, which comprises a variable cross-section spiral pipe, the diameter of the inlet end of the variable cross-section spiral pipe is larger than the diameter of the outlet end of the variable cross-section spiral pipe; a plurality of MPP plates are installed in the variable cross-section spiral pipe, one of the MPP plates is embedded in the inlet end of the variable cross-section spiral pipe, and the other MPP plates are sequentially embedded in the inside of the variable cross-section spiral pipe at the same interval, forming a multi-stage MPP plate composite sound absorption structure; the cross-section pipe diameter of the variable cross-section spiral pipe linearly decreases from the inlet end of the variable cross-section spiral pipe to the outlet end of the variable cross-section spiral pipe. The gradient design of the variable cross-section spiral pipe integrated with the micro-perforated panel realizes low-frequency broadband high-efficiency sound absorption in a compact space, avoids the problem of heavy structure caused by the deep and large back cavity in the traditional technology, and overcomes the limitation of narrow sound absorption frequency band, and is especially suitable for space-limited occasions, and can balance the low-frequency performance and broadband characteristics in a limited space.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of low-frequency sound absorption, and particularly relates to a micro-perforated panel composite gradient spiral pipe sound absorption device and method. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] Noise control, especially the suppression of low-frequency broadband noise, is a key challenge faced by many industrial fields. Traditional technologies such as porous materials and resonant structures (such as Helmholtz resonators, micro-perforated panels) have inherent limitations in achieving "low frequency, wide band, high efficiency" sound absorption: porous materials and traditional micro-perforated panel structures need to rely on deep and large back cavities to improve low-frequency performance, resulting in a bulky structure that contradicts the trend of modern equipment compactness and lightness; the resonant structure sound absorption frequency band of Helmholtz resonator is extremely narrow, and the simple parallel connection of multiple resonant units to widen the frequency band will sharply increase the complexity and space occupation of the system. Therefore, traditional technologies cannot simultaneously achieve low-frequency high efficiency and wide-band sound absorption in limited space.

[0004] To solve the above technical problems, the prior art discloses a spiral channel micro-perforated sound absorption device, which comprises a shell, an outer spiral structure, an inner spiral structure and a micro-perforated panel (hereinafter referred to as MPP panel). The outer spiral structure comprises four spiral outer ring channels, and the inner spiral structure comprises two spiral inner ring channels. Each spiral channel is provided with a channel baffle at the lower end. The micro-perforated panel is provided with six corresponding perforated parts, each perforated part corresponds to the upper end opening of each spiral channel, forming six sound absorption units. Each channel baffle is set to different heights, so that the lengths of each spiral channel are different, so that each sound absorption unit has a different acoustic path, and each sound absorption unit has a different working frequency. When the sound wave frequency enters the working frequency band of each sound absorption unit, impedance matching is generated.

[0005] The above scheme has the following defects:

[0006] The above scheme adopts a multi-channel independent layout, and each channel needs to be provided with a baffle and a micro-perforated part separately, resulting in a large number of components, complex assembly and high manufacturing cost. Each sound absorption channel is independently provided, so there is a lack of effective acoustic coupling between each sound absorption unit, making it difficult to form a smooth and continuous sound absorption curve. SUMMARY

[0007] Therefore, the purpose of the present application is to provide a micro-perforated panel composite gradient spiral pipe sound absorption device and method, which can solve the technical problems of the prior art, i.e. the use of a multi-channel independent layout, the need for separate setting of a baffle and a micro-perforated part for each channel, resulting in a large number of components, complex assembly, high manufacturing cost, and a lack of effective acoustic coupling between each sound absorption unit.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, a micro-perforated plate composite gradient spiral tube sound absorption device is provided, including a variable cross-section spiral tube, wherein the inlet diameter of the variable cross-section spiral tube is larger than the outlet diameter of the variable cross-section spiral tube.

[0010] Several MPP plates are installed inside the variable cross-section spiral tube. One MPP plate is embedded in the inlet end of the variable cross-section spiral tube, and the other MPP plates are embedded in the variable cross-section spiral tube at equal intervals to form a multi-level MPP plate composite sound absorption structure.

[0011] The cross-sectional diameter of the variable cross-section spiral tube decreases linearly from the inlet end to the outlet end.

[0012] Preferably, the installation position of the MPP plate to the inlet end of the variable cross-section spiral tube is as follows: The MPP plates at each level are spaced evenly, and several microholes are evenly opened on the surface of the MPP plates, with the inlet end of the variable cross-section spiral tube as the starting point. The diameter of the microholes on each MPP plate is... Perforation rate , plate thickness All adopt a gradient design.

[0013] Preferably, the diameter of the variable cross-section spiral pipe changes continuously according to the following variation pattern:

[0014] ;

[0015] In the formula: The inlet diameter of the variable cross-section spiral pipe; The outlet diameter of the variable cross-section spiral pipe; It is a helix (the central axis of the variable cross-section helical tube, which is also the helical channel). Pipe diameter at the location; This refers to a specific location on the spiral channel. ;

[0016] The length of the spiral is... , The overall height of the variable cross-section spiral tube. The diameter of the helix. The pitch is the screw pitch.

[0017] Preferred, The diameter variation law of the variable cross-section spiral pipe remains unchanged, and the pitch is kept constant. Designed for variable pitch Variable pitch along The pattern of change is as follows:

[0018] ;

[0019] In the formula: For physical height at When the pitch changes, ; The pitch at the inlet end of the variable cross-section spiral tube; The pitch at the outlet end of the variable cross-section spiral pipe; The overall height of the variable-pitch, variable-section spiral tube. .

[0020] Preferably, for variable pitch structures, the total length of the helix is... The following can be obtained through numerical integration:

[0021] Arc length infinitesimal element of the spiral for:

[0022] ;

[0023] In the formula: The radius of the helix; This refers to the physical height of the micro-spiral segment; The radial length of the micro-helical segment;

[0024] .

[0025] Preferably, the variable cross-section spiral tube and MPP plate are made of metal or engineering plastic.

[0026] Secondly, a method for adjusting the aforementioned micro-perforated plate composite gradient spiral tube sound absorption device is provided, the specific steps of which include:

[0027] S1. Establish the acoustic unit model:

[0028] The transfer matrix of the micro-perforated plate model is: ;

[0029] In the formula: ; For the first Acoustic impedance of the MPP board;

[0030] The transfer matrix for the variable cross-section helical tube model is: ;

[0031] In the formula: , , Speed ​​of sound in air; ; ; , air characteristic impedance, , For the first The aperture of the micro-segment straight tube;

[0032] S2. Combine the above unit models into a total transfer matrix:

[0033] ... ;

[0034] S3. Calculate the surface acoustic impedance from the total transfer matrix. Reflection coefficient and sound absorption coefficient :

[0035] ;

[0036] In the formula: This refers to the element in the first row and first column of the total transfer matrix; The element in the second row and first column of the total transfer matrix;

[0037] like If the expected results are not achieved, adjust the parameters of the MPP board or the geometric parameters of the variable cross-section spiral tube, and repeat steps S1 to S3 until the sound absorption coefficient curve reaches the expected results.

[0038] Preferred, the first Acoustic impedance of MPP board ;

[0039] ;

[0040] In the formula: air density; The coefficient of dynamic viscosity; For the first The pore size of the micropores in the MPP board; For the first The perforation rate of the MPP board; For the first The thickness of the MPP board; is the perforation constant.

[0041] Preferably, adjusting the geometric parameters of the variable cross-section helical tube can reduce the pitch. Or increase the diameter of the spiral Or reduce the variable pitch The pitch at the outlet end increases the sound absorption performance.

[0042] Preferably, when adjusting the parameters of the MPP board, the aperture can be reduced. Or reduce the perforation rate Or reduce the plate thickness Or increase the placement location The spacing increases the sound absorption performance.

[0043] Compared with the prior art, the advantages and positive effects of this invention are:

[0044] The variable cross-section helical tube in this invention effectively increases the acoustic path length, introducing a sound wave phase delay effect within a limited axial space and reducing the overall fundamental frequency of the system. Embedding multiple gradient-designed micro-perforated plates within the variable cross-section helical tube can excite local resonances at their respective characteristic frequencies, forming multiple discrete sound absorption peaks and achieving broadband impedance matching. This invention achieves low-frequency broadband and efficient sound absorption in a compact space through the gradient design of the micro-perforated plate integrated into the variable cross-section helical tube, avoiding the structural bulkiness caused by the reliance on deep and large back cavities in traditional technologies. It also overcomes the limitation of narrow sound absorption bandwidth, making it particularly suitable for applications in space-constrained environments. Compared to the independent multi-channel layout in the prior art, this invention simplifies the structure and promotes acoustic coupling by embedding multiple gradient-designed MPP plates within a single variable cross-section helical tube, achieving both low-frequency performance and broadband characteristics within a limited space. Attached Figure Description

[0045] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0046] Figure 1 This refers to the fixed pitch of Embodiment 1 or Embodiment 2 of the present invention. A schematic diagram of the structure of a variable cross-section spiral tube;

[0047] Figure 2 This is a schematic diagram of the structure of the MPP board according to Embodiment 1 or Embodiment 2 of the present invention;

[0048] Figure 3 This is the variable pitch version of Embodiment 1 or Embodiment 2 of the present invention. A schematic diagram of the structure of a variable cross-section spiral tube;

[0049] Figure 4 This is a comparison diagram of the sound absorption curves of the first-stage MPP composite structure, the second-stage MPP composite structure, and the third-stage MPP composite structure of Embodiment 2 of the present invention;

[0050] Figure 5 This is a comparison diagram of the sound absorption curves of the three-stage MPP composite structure and the four-stage MPP composite structure in Embodiment 2 of the present invention;

[0051] Figure 6 This refers to different pitches in Embodiment 2 of the present invention. Comparison of sound absorption curves of the three-stage MPP composite structure;

[0052] Figure 7Different spiral diameters in Embodiment 2 of the present invention Comparison of sound absorption curves of the three-stage MPP composite structure;

[0053] Figure 8 This refers to different pitch variations in Embodiment 2 of the present invention. With pitch Comparison of sound absorption curves of the three-stage MPP composite structure;

[0054] Figure 9 This is a comparison diagram of the sound absorption curves of the three-stage MPP composite structure with increased pore size and original pore size in Embodiment 2 of the present invention;

[0055] Figure 10 This is a comparison diagram of the sound absorption curves of the three-stage MPP composite structure with increased perforation rate and original perforation rate in Embodiment 2 of the present invention.

[0056] Figure 11 This is a comparison diagram of the sound absorption curves of the three-stage MPP composite structure with increased plate thickness and original plate thickness in Embodiment 2 of the present invention;

[0057] Figure 12 This is a comparison diagram of the sound absorption curves of the three-stage MPP composite structure in the compact position and the original position in Embodiment 2 of the present invention;

[0058] In the picture:

[0059] 1. Variable cross-section spiral tube; 2. MPP board. Detailed Implementation

[0060] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0061] The present invention will now be described in detail with reference to the accompanying drawings.

[0062] Example 1

[0063] This embodiment discloses a micro-perforated plate composite gradient spiral tube sound absorption device (hereinafter referred to as the device), such as Figure 1 As shown, it includes a variable cross-section helical tube 1, which is a three-dimensional acoustic channel that spirals upward around a central axis. The diameter of the inlet end of the variable cross-section helical tube 1 is larger than the diameter of the outlet end of the variable cross-section helical tube 1; as Figure 1As shown, the incident sound wave enters from the inlet end of the variable cross-section spiral tube 1. Along the propagation path of the incident sound wave, several MPP plates 2 are installed inside the variable cross-section spiral tube 1. One MPP plate 2 is embedded in the inlet end of the variable cross-section spiral tube 1, and the other MPP plates 2 are embedded in the variable cross-section spiral tube 1 at equal intervals to form a multi-level MPP plate composite sound absorption structure (hereinafter referred to as multi-level sound absorption structure).

[0064] like Figure 1 As shown, in this embodiment, the cross-sectional diameter of the variable cross-section spiral tube 1 decreases linearly from the inlet end to the outlet end. It should be noted that the linearly decreasing cross-sectional diameter design of the variable cross-section spiral tube 1 achieves an acoustic black hole effect.

[0065] Compared to traditional deep-cavity designs, the variable-section helical tube 1 effectively increases the acoustic path by several times the physical height at the same physical height, thereby lowering the overall fundamental frequency of the device. This creates the necessary conditions for exciting and enhancing low-frequency resonance, achieving a sound wave phase delay effect. Furthermore, as the incident sound wave flows through the entire variable-section helical tube 1, it is continuously affected by the viscous boundary layer of the tube wall, resulting in broadband sound energy attenuation. This allows the device in this embodiment to achieve excellent low-frequency sound absorption performance without relying on a traditional large-volume back cavity. Compared to traditional MPP plate structures that require a deep cavity, the multi-stage sound absorption structure in this embodiment can reduce the physical height of the device while maintaining the same low-frequency target, greatly improving space utilization and making it particularly suitable for applications in space-constrained environments.

[0066] It should also be noted that, such as Figure 1 As shown, after the incident sound wave enters the variable cross-section helical tube 1, it passes through multiple MPP plates 2 in sequence for noise reduction. In this embodiment, the multi-stage MPP plates 2 divide the variable cross-section helical tube 1 into resonant cavities connected in series, which can broaden the effective sound absorption bandwidth, enhance the low-frequency sound absorption performance, and, combined with the sound wave phase delay effect and propagation loss effect of the variable cross-section helical tube 1, form a broadband impedance matching.

[0067] In this embodiment, the placement position of the MPP plate 2 at the inlet end of the variable cross-section spiral tube 1 is as follows: The spacing between each level of MPP board 2 is consistent (i.e.) This ensures uniform distribution along the acoustic path, promotes effective acoustic coupling between each MPP board 2, avoids obvious valleys in the sound absorption curve, and prevents excessively strong or weak acoustic coupling.

[0068] like Figure 2 As shown, a plurality of microholes are uniformly formed on the surface of the MPP plate 2. In this embodiment, the inlet end of the variable cross-section spiral tube 1 is the starting point, and the numbers of each MPP plate increase sequentially. The aperture of the microholes on each MPP plate 2 is... for Gradient design; perforation rate of micropores on each MPP board 2 for Gradient design; thickness of each MPP board 2 for Gradient design.

[0069] It should be noted that in this embodiment, the parameters of the MPP board 2 are designed with a gradient to achieve wideband impedance matching and thus superior sound absorption performance. Specifically, the MPP board 2 with gradient parameter design can generate strong local resonances at their respective characteristic frequencies at their respective positions within the variable cross-section helical tube 1, concentrating the consumption of sound energy and forming multiple sound absorption peaks and multi-level discrete resonances.

[0070] It is understandable that as the incident sound wave flows through the entire variable cross-section helical tube 1, it is continuously subjected to the viscous boundary layer of the tube wall, resulting in broadband sound energy attenuation and forming distributed broadband dissipation. In this embodiment, by employing multiple MPP plates 2 with different parameters, multiple discrete resonant absorption peaks are excited within a set frequency range (in this embodiment, this set frequency is 100-1000Hz). These resonant absorption peaks, combined with the distributed broadband viscous dissipation provided by the variable cross-section helical tube 1, can significantly broaden the effective sound absorption bandwidth of the device. At the same time, the phase delay effect of the variable cross-section helical tube allows the device to achieve excellent low-frequency sound absorption performance without relying on a traditional deep and large back cavity, greatly reducing the axial dimension and improving space utilization, making it particularly suitable for space-constrained applications.

[0071] In this embodiment, the diameter of the variable cross-section helical tube 1 changes continuously along the propagation path of the incident sound wave according to the following requirements:

[0072] ;

[0073] In the formula: The inlet diameter of the variable cross-section spiral pipe; The outlet diameter of the variable cross-section spiral pipe; It is a helix (the central axis of the variable cross-section helical tube, which is also the helical channel). Pipe diameter at the location; This refers to a specific location on the spiral channel. ;

[0074] The length of the spiral is... , The overall height of the variable cross-section spiral tube. The diameter of the helix. The pitch is the screw pitch.

[0075] It should be noted that the diameter of the variable cross-section spiral tube 1 is changed by linearly decreasing, which can avoid sound wave reflection and energy loss caused by sudden changes in the diameter, and ensure the continuity of sound wave propagation.

[0076] Although the variable cross-section helical tube 1 effectively increases the acoustic path length and reduces the system fundamental frequency, the fixed pitch design makes it difficult to further compress the overall thickness of the structure while maintaining the same acoustic wave propagation path length. This limits the improvement of space utilization, especially in space-constrained application scenarios where it is difficult to achieve a more compact layout.

[0077] like Figure 3 As shown, in order to further improve space utilization while ensuring the same sound wave propagation path length, Under the condition of pitch Designed for variable pitch Variable pitch The diameter of the variable cross-section spiral tube 1 decreases continuously from top to bottom along its physical height direction. This design can further reduce the overall thickness of the device. It should be noted that the diameter variation pattern of the variable cross-section spiral tube 1 remains unchanged.

[0078] Specifically, variable pitch along The pattern of change is as follows:

[0079] ;

[0080] In the formula:

[0081] For physical height at When the pitch changes, ;

[0082] The pitch at the inlet end of the variable cross-section spiral tube 1;

[0083] The pitch at the outlet end of the variable cross-section spiral tube 1;

[0084] The overall height of the variable pitch, variable cross-section spiral tube 1 is given. .

[0085] In this embodiment, while ensuring the length of the sound wave propagation path... Without changing the pitch, Designed as a variable pitch helix with a linear decrease along the physical height direction of the variable cross-section helical tube 1. This causes the spiral density to gradually increase from the inlet end to the outlet end of the variable cross-section spiral tube 1, effectively compressing the physical dimensions of the device without changing the diameter variation law of the variable cross-section spiral tube 1.

[0086] In this embodiment, pitch The linearly decreasing change, in conjunction with the change in the diameter of the variable cross-section helical tube 1, forms a synergistic control mechanism. This maintains the gradual diameter control mechanism that the incident sound wave continuously experiences during propagation, while also controlling the pitch... The linearly decreasing change enhances the superposition of the acoustic wave phase delay effect, ultimately achieving a balance between the equivalent extension of the acoustic path length and structural compactness within a limited installation space.

[0087] Because the diameter and pitch of the variable cross-section helical tube 1 change continuously in physical height, the length of the helix cannot be directly determined by a simple geometric formula. This results in a deviation in the calculation of the acoustic path length when mapping the three-dimensional helical structure to a one-dimensional straight tube model, which in turn leads to inaccurate prediction of sound absorption performance.

[0088] In this embodiment, for the variable pitch structure, the total length of the helix is... The derivation formula is obtained through numerical integration and is as follows:

[0089] From the perspective of differential geometry, the arc length of a spiral is a differential element. for:

[0090] ;

[0091] In the formula:

[0092] The radius of the helix;

[0093] This refers to the physical height of the micro-spiral segment;

[0094] The radial length of the micro-helical segment;

[0095] Therefore, the total length of the spiral can be calculated. for:

[0096] ;

[0097] The reason for calculating the total helix length for the above physical model is to map the three-dimensional helical structure to a one-dimensional intuitive model, and then use the transfer matrix theory method to calculate its sound absorption performance.

[0098] In this embodiment, the variable cross-section spiral tube 1 and the MPP plate 2 are made of metal or engineering plastic. The metal material can be a metal alloy with high chemical stability, such as stainless steel or aluminum alloy. Its dense surface structure effectively blocks moisture penetration, preventing acoustic parameter drift caused by moisture absorption. Due to its high chemical stability and thermal conductivity, the metal material effectively blocks moisture penetration in humid environments and maintains structural rigidity to prevent thermal deformation under high-temperature conditions. The engineering plastic can be a high-performance polymer such as polycarbonate or polyetheretherketone. The dense molecular chains ensure dimensional stability under alternating temperature and humidity conditions, eliminating fiber breakage or adhesive aging.

[0099] If traditional porous materials are used, they will face problems such as performance degradation, structural aging and material shedding caused by moisture absorption and expansion, thermal degradation or chemical corrosion in humid and high temperature environments. This will lead to unstable sound absorption performance or even failure, which will seriously restrict the long-term reliability and applicability of the device under complex working conditions in industrial sites.

[0100] Example 2

[0101] This embodiment discloses an adjustment method for a micro-perforated plate composite gradient spiral tube sound absorption device, which applies the micro-perforated plate composite gradient spiral tube sound absorption device disclosed in Embodiment 1. The specific steps include:

[0102] S1. Establish acoustic unit models of micro-perforated plates and variable cross-section spiral tubes;

[0103] Micro-perforated plate model: Part The MPP board 2 is considered as a lumped acoustic impedance element, and its transfer matrix is:

[0104] ;

[0105] In the formula:

[0106] Let be the area of ​​the incident surface. ;

[0107] For the first Acoustic impedance of MPP board 2 ,

[0108] ;

[0109] In the formula:

[0110] air density;

[0111] The coefficient of dynamic viscosity;

[0112] ;

[0113] Angular frequency;

[0114] For the first The pore size of the micropores in the MPP board 2;

[0115] For the first The perforation rate of MPP board 2;

[0116] For the first The thickness of MPP board 2;

[0117] is the perforation constant.

[0118] Variable cross-section helical tube model: Discretize the variable cross-section helical tube 1 along the direction of the helix as follows: Straight pipe sections with gradually changing cross-sectional areas, the first The transfer matrix for the straight pipe section is:

[0119] ;

[0120] In the formula:

[0121] The complex wave number (considering damping) is given. , Angular frequency, Speed ​​of sound in air;

[0122] ;

[0123] The length of each micro-segment of straight pipe after discretization. , The total length of the variable cross-section spiral tube 1;

[0124] For dependent on local cross-sectional area acoustic impedance, , air characteristic impedance, , For the first The aperture of the micro-segment straight pipe.

[0125] S2, Composite Total Transfer Matrix;

[0126] The acoustic unit model in step S1 above is constructed based on the transfer matrix method (TMM), which decomposes the complex composite structure into a series of basic acoustic units connected in series. The propagation of sound waves in the entire structure can be described by matrix multiplication.

[0127] The overall transfer matrix is ​​synthesized from the individual unit models of S1. The quadrupole parameter matrix connecting the input-output relationship of sound pressure and velocity is as follows:

[0128] ;

[0129] In the formula:

[0130] Sound pressure level;

[0131] Volume velocity;

[0132] For the first The transfer matrix of MPP board 2;

[0133] For the variable cross-section spiral tube 1 The transfer matrix of the straight tube layer;

[0134] The total transfer matrix is ​​obtained based on the actual layout of the device. For example, for a device with a three-level MPP board 2, ;

[0135] S3, Acoustic performance calculation;

[0136] Calculate the surface acoustic impedance from the total transfer matrix in step S2. Reflection coefficient and sound absorption coefficient :

[0137] ;

[0138] In the formula:

[0139] Let be the area of ​​the incident surface;

[0140] Air characteristic impedance;

[0141] This refers to the element in the first row and first column of the total transfer matrix;

[0142] The element in the second row and first column of the total transfer matrix;

[0143] The sound absorption coefficient curve calculated using the above model can verify the sound absorption performance of the device. If it does not meet expectations, return to adjust the parameters of MPP plate 2 (such as aperture). or perforation rate Or plate thickness Or placement location ) or the geometric parameters of the variable cross-section helical tube 1 (such as pitch) or helix diameter or variable pitch Repeat steps S1 to S3 until the sound absorption coefficient curve reaches the expected value.

[0144] To verify and demonstrate the synergistic effect of the multi-stage MPP board 2 design on improving sound absorption performance, in this embodiment, the geometric parameters of the variable cross-section spiral tube 1 are kept unchanged. By comparing the sound absorption coefficients of the first-stage MPP composite structure, the second-stage MPP composite structure, and the third-stage MPP composite structure, the performance advantages brought by different MPP boards 2 are verified.

[0145] In this embodiment, the parameters of the variable cross-section helical tube 1 are set as follows: overall height. 50mm, pitch 10mm, spiral diameter The inlet diameter is 40mm. 10mm, end aperture It is 0.

[0146] The parameters of the multi-level MPP board are shown in Table 1;

[0147] Table 1 Parameter Details of Multi-Level MPP Board

[0148]

[0149] like Figure 4 The comparison of sound absorption curves for the single-stage, two-stage, and three-stage MPP composite structures shows that the three-stage MPP composite structure has a higher sound absorption performance than the two-stage structure, and the two-stage structure has a higher sound absorption performance than the single-stage structure. Increasing the number of MPP stages improves the overall sound absorption performance, especially the low-frequency performance. Furthermore, there is a synergistic effect between the multi-stage MPP boards. The coupling and interaction between the MPP boards and the variable cross-section spiral tube 1 not only avoids mutual interference but also smooths and broadens the overall sound absorption frequency band.

[0150] This embodiment achieves wide-bandwidth, high-efficiency sound absorption from high to low frequencies by configuring different apertures and perforation rates on MPP boards 2 at different locations.

[0151] In this embodiment, an additional MPP board 2 is added to the three-level MPP composite structure to form a four-level MPP composite structure, such as... Figure 5As shown, the sound absorption performance of the four-stage MPP composite structure is not significantly different from that of the three-stage MPP composite structure. That is, for multi-stage MPP composite structures after the third stage, the overall improvement in sound absorption performance gradually decreases, and the increase in the sound absorption coefficient shows a convergent trend. This phenomenon is consistent with the physical law of sound energy attenuation, that is, when the sound wave passes through the preceding MPP board, its energy has been significantly dissipated, resulting in limited sound energy that can be applied by subsequent MPP boards.

[0152] Therefore, considering factors such as the improvement of sound absorption performance, structural complexity, manufacturing cost, and processing difficulty, the three-stage MPP composite structure is the optimal choice. The three-stage MPP composite structure can effectively achieve low-frequency broadband sound absorption and avoid diminishing returns caused by over-design, thus balancing "sound absorption performance" and "engineering feasibility".

[0153] In this embodiment, the sound absorption coefficient curve calculated by steps S1-S3 can be used to verify the sound absorption performance of the device. If it does not meet expectations, the influence of each parameter of the variable cross-section spiral tube 1 on the sound absorption performance of the device can be explored by adjusting the geometric parameters of the variable cross-section spiral tube 1. Then, the sound absorption coefficient curve can be adjusted to meet expectations by adjusting the corresponding geometric parameters.

[0154] Understandably, given that the three-stage MPP composite structure is the optimal choice, by fixing the parameters of the three-stage MPP plate (refer to Table 1) and changing the geometric parameters of the variable cross-section helical tube 1, we can explore the various parameters of the variable cross-section helical tube 1 (pitch). Helix diameter Variable pitch The influence of sound absorption performance of the device.

[0155] In this embodiment, the helix height is fixed. 50mm, pitch Spiral diameter and variable pitch The parameter changes are shown in Table 2;

[0156] Table 2. Details of Geometric Parameter Variations for Variable Cross-Section Spiral Tube 1

[0157]

[0158] from Figure 6 Different pitches shown The comparison of the sound absorption curves shows that reducing the pitch... It can extend the equivalent sound path, enhance the phase delay effect, and strengthen the coupling effect with the multi-stage MPP board, thereby effectively improving the low-frequency sound absorption performance.

[0159] from Figure 7 Different helix diameters shown A comparison of the sound absorption curves shows that increasing the spiral diameter... It can effectively enhance low-frequency performance, but in practical applications, it is necessary to comprehensively consider the balance between device structure and performance. For example, although a larger spiral diameter enhances low-frequency sound absorption, it limits the application scenarios, while reducing the spiral diameter helps to achieve a compact structure, which can serve different application scenarios.

[0160] from Figure 8 The variable pitch shown The comparison of the sound absorption curves shows that the variable pitch design can achieve better acoustic impedance matching, improve peak sound absorption efficiency, and reduce the required variable pitch without changing the basic structural dimensions. The pitch at the outlet end can improve sound absorption performance. It should be noted that... Figure 8 pitch in 10mm is used as a comparative example. Figure 8 The pitch of 10-7.5mm refers to a variable pitch that decreases linearly from 10mm to 7.5mm. , Figure 8 The 10-5mm pitch in the text refers to a variable pitch that decreases linearly from 10mm to 5mm. .

[0161] It is understandable that in application scenarios with limited service space, reducing the spiral diameter is appropriate. At that time, variable pitch can be designed. make up.

[0162] In this embodiment, the sound absorption coefficient curve calculated by steps S1-S3 can be used to verify the sound absorption performance of the device. If it does not meet expectations, the influence of each parameter of the multi-level MPP board on the sound absorption performance of the device can be explored by adjusting the parameters of the multi-level MPP board. Then, the sound absorption coefficient curve can be adjusted to meet expectations by adjusting the parameters of the multi-level MPP board, thereby achieving precise acoustic tuning.

[0163] Verify the parameters (aperture) of the multi-level MPP board. Perforation rate , plate thickness Placement location When considering the impact of sound absorption performance, a three-stage MPP composite structure is used as the basis, and the geometric parameters (overall height) of the variable cross-section spiral tube 1 are fixed. 50mm, pitch 10mm, spiral diameter (40mm), using the controlled variable method, only one parameter of the multi-level MPP board is changed each time.

[0164] Specifically, the parameters of the multi-stage MPP board are shown in Table 1. First, increase the aperture... With all other parameters remaining unchanged, the increased aperture is: mm, mm, mm. For example, Figure 9 The comparison of sound absorption curves with increased aperture and original aperture shown demonstrates that increasing the aperture of the multi-stage MPP board leads to a decrease in low-frequency sound absorption performance.

[0165] Next, increase the perforation rate while keeping other parameters unchanged. The increased perforation rate is... , , .like Figure 10 The comparison of sound absorption curves with increased perforation rate versus original perforation rate shows that increasing the perforation rate of multi-stage MPP boards leads to a decrease in low-frequency sound absorption performance.

[0166] Then, the plate thickness was increased while other parameters remained unchanged. The increased plate thickness was: mm, mm, mm. For example, Figure 11 The comparison of sound absorption curves with increased board thickness and original board thickness shows that increasing the thickness of the multi-stage MPP board will increase the acoustic quality and acoustic impedance of the multi-stage MPP board, causing its resonance peak to shift to lower frequencies, accompanied by a decrease in peak value. This will also lead to a decrease in low-frequency sound absorption performance, and at the same time, it will also affect high-frequency sound absorption.

[0167] Finally, the installation position was changed to a more compact one, i.e., the spacing between the placement positions was reduced, while other parameters remained unchanged. The placement position after reducing the spacing is as follows: mm, mm, mm, such as Figure 12 The comparison of the sound absorption curves of the compact position and the original position shows that reducing the spacing between the placement positions, i.e. reducing the placement position of each level of MPP board, has no significant impact on low-frequency sound absorption, but will reduce the overall sound absorption performance of the device.

[0168] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A micro-perforated panel composite gradient helical pipe sound absorption device, characterized in that, The variable cross-section spiral pipe has an inlet end with a diameter larger than that of an outlet end; The variable cross-section spiral pipe is provided with a plurality of micro-perforated plates, one of which is embedded in the inlet end of the variable cross-section spiral pipe, and the other micro-perforated plates are embedded in the variable cross-section spiral pipe at equal intervals to form a multi-stage micro-perforated plate composite sound absorption structure; the cross-section diameter of the variable cross-section spiral pipe linearly decreases from the inlet end to the outlet end; The micro-perforated plate is arranged at the inlet end of the variable cross-section spiral pipe The micro-perforated plates are uniformly spaced, and the plate surface of the micro-perforated plate is uniformly provided with a plurality of micro-holes; the micro-holes on the micro-perforated plates are designed in a gradient manner from the inlet end of the variable cross-section spiral pipe as a starting point , the perforation rate , and the plate thickness ​ The cross-section diameter of the variable cross-section spiral pipe continuously changes according to the following change rule: ; wherein: Din is the tube diameter at the inlet end of the variable cross-section spiral tube; Dout is the tube diameter at the outlet end of the variable cross-section spiral tube; D is the tube diameter at a position along the spiral line D is the tube diameter at a position along the spiral line D is the tube diameter at a position along the spiral line D is the tube diameter at a position along the spiral line is the length of the helix, , is the overall height of the variable cross-section helix, is the helix diameter, is the pitch; The The pipe diameter of the constant and variable cross-section spiral pipe changes regularly, and the pitch The design is variable pitch , variable pitch The change rule of the pitch is: ; wherein: is the physical height of the variable pitch, variable pitch at the inlet end of the variable cross-section spiral pipe; ; is the pitch at the inlet end of the variable cross-section spiral pipe; is the pitch at the outlet end of the variable cross-section spiral pipe; is the overall height of the variable pitch, variable cross-section spiral pipe, .

2. A micro-perforated panel composite gradient helical pipe sound absorption device according to claim 1, characterized in that, the total length of the helical line By numerical integration, it is found that Arc length element of a helix Is: ; wherein: is the helix radius; is the physical height of the micro-helix segment; is the radial length of the micro-helix segment; 。 3. A micro-perforated panel composite gradient helical pipe sound absorption device according to claim 1, characterized in that, The variable cross-section spiral pipe and the micro-perforated plate are made of metal or engineering plastic.

4. A method of adjusting a micro-perforated panel composite gradient helix pipe sound absorption device according to any one of claims 1-3, characterized in that, The specific steps include: S1, establishing an acoustic unit model; The transfer matrix of the micro-perforated panel model is: ; In the formulae: ; is the acoustic impedance of the first level micro-perforated panel. The transfer matrix of the variable cross-section spiral tube model is: ; wherein: ， , is the speed of sound in air; ; ; , is the air characteristic impedance, , is the diameter of the microsection straight tube of the first layer; S2, synthesizing the total transfer matrix of the above unit models: ... ; S3. Surface acoustic impedance from total transfer matrix , reflection coefficient and absorption coefficient : ; wherein: is the first row first column element of the total transfer matrix; is the second row first column element of the total transfer matrix; If If the desired is reached, the parameters of the micro-perforated panel or the geometry of the variable cross-section spiral duct are adjusted and steps S1 to S3 are repeated until the curve of the coefficient of absorption reaches the desired.

5. The tuning method of a micro-perforated panel composite gradient- helix duct sound absorption device according to claim 4, characterized in that, The first acoustic impedance of the microperforated panel ; ; wherein: is the air density; is the dynamic viscosity coefficient; is the pore diameter of the micro-pores of the micro-porous plate of the is the pore diameter of the micro-pores of the micro-porous plate of the is the porosity of the micro-porous plate of the is the porosity of the micro-porous plate of the is the plate thickness of the micro-porous plate of the is the plate thickness of the micro-porous plate of the is the porosity of the micro-porous plate of the 6. The tuning method of a micro-perforated panel composite gradient- helix duct sound absorption device according to claim 4, characterized in that, Adjusting the geometry of the variable cross-section spiral can reduce the pitch or increase the diameter of the spiral or reduce the variable pitch The exit end pitch increases the sound absorption performance.

7. The tuning method of a micro-perforated panel composite gradient- helix duct sound absorption device according to claim 4, characterized in that, Adjusting the parameters of the micro-perforated panel can reduce the hole diameter or reduce the perforation rate or reduce the panel thickness or increase the distance of the placement position to increase the sound absorption performance.

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