Pipe high-frequency muffler based on acoustic mode modulation and perforated tube and design method thereof

Abstract

The application discloses a pipeline high-frequency muffler based on acoustic mode modulation and perforated pipe, which comprises a shell, a cylindrical inner pipe connected in the shell through a plurality of partitions, the plurality of partitions are axially parallel to the inner pipe and are uniformly arranged along the circumference of the inner pipe, the plurality of partitions divide an annular cavity formed between the shell and the inner pipe into a plurality of sub-cavities with the same size, and flanges are connected to both ends of the shell. The application also discloses a design method of the pipeline high-frequency muffler based on acoustic mode modulation and perforated pipe, which comprises a perforation design method of the inner layer of the shell and / or the inner layer of the inner pipe and a design method of the partitions. The pipeline high-frequency muffler based on acoustic mode modulation and perforated pipe solves the problem that the existing technology uses sound-absorbing materials which are prone to failure and harmful to human health to realize high-frequency noise suppression. The pipeline high-frequency muffler uses the partitions and the perforated pipe to realize high-frequency noise elimination, and has the advantages of simple structure and convenient dismounting and replacement.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of pipeline high-frequency noise suppression device, and particularly relates to a pipeline high-frequency muffler based on acoustic mode modulation and perforated pipe. BACKGROUND

[0002] Pipelines are widely used in the fields of oil and gas transportation, automobiles, nuclear power and ships. At present, with the widespread use of turbocharged engines, gas turbines, centrifugal fans, axial flow fans and other turbomachinery, the medium and high frequency noise presented in the pipeline or at the outlet is significant, which not only affects the environmental comfort and the health of the surrounding personnel, but also can cause the failure of the equipment due to acoustic fatigue in severe cases.

[0003] At present, the high-frequency noise suppression in the pipeline mainly adopts a resistive muffling structure containing sound-absorbing materials. However, the sound-absorbing materials are prone to failure in harsh working conditions such as high temperature, high humidity, dust, oil mist and corrosive gas. At the same time, the fibers of the sound-absorbing materials are very small and can easily enter the human body through the respiratory tract in high-speed airflow, which is harmful to human health. SUMMARY

[0004] The purpose of the present application is to provide a pipeline high-frequency muffler based on acoustic mode modulation and perforated pipe, which solves the problem of using sound-absorbing materials that are prone to failure and harmful to human health to achieve high-frequency noise suppression. The present application uses a partition and a perforated pipe to achieve high-frequency muffling, which is simple in structure and convenient to disassemble and replace.

[0005] The technical scheme adopted by the present application is a pipeline high-frequency muffler based on acoustic mode modulation and perforated pipe, which comprises an outer shell, a cylindrical inner pipe connected inside the outer shell by a plurality of partitions; the plurality of partitions are axially parallel to the inner pipe and are uniformly arranged along the circumference of the inner pipe, and the plurality of partitions divide the annular cavity formed between the outer shell and the inner pipe into a plurality of sub-cavities of the same size; the two ends of the outer shell are connected with flanges.

[0006] The present application is characterized in that:

[0007] The outer shell is a double-layer structure; the inner pipe is a double-layer cylindrical structure with a "front circle and rear sharp" airfoil shape; the inner layer of the outer shell and the inner layer of the inner pipe are divided into two regions in the axial direction, a plurality of micro-holes are uniformly distributed in one region, and a plurality of ordinary holes are uniformly distributed in the other region; the micro-holes and the ordinary holes are uniformly distributed.

[0008] The pore size of the micro-holes ranges from 0.1mm to 1mm, and the pore size of the ordinary holes ranges from 1mm to 5mm; the perforation rate of the micro-holes and the ordinary holes is 0.1% to 15%.

[0009] The diameter of the contact part between the outer shell and the partition is greater than the diameter of the two ends of the outer shell.

[0010] The partition is a rectangular metal plate connecting the inner layer of the shell and the outer layer of the inner tube.

[0011] The number of the partitions is at least three, and the length of the partitions is equal to the length of the perforated part of the inner layer of the inner tube.

[0012] Another technical solution of the present application is a design method of a pipeline high-frequency muffler based on acoustic mode modulation and perforated tube, including a perforation design method of the inner layer of the shell and / or the inner layer of the inner tube and a design method of the partition.

[0013] The design method of the perforation of the inner layer of the shell and / or the inner layer of the inner tube is characterized in that:

[0014] The perforation design method of the inner layer of the shell and / or the inner layer of the inner tube is designed with transmission loss as an index, and specifically:

[0015] For a perforated tube with a length of l p , the sound pressure p1(0) at the inlet x=0, the sound particle velocity u1(0) and the sound pressure p1(l p ) at the outlet x=l p , and the sound particle velocity u1(l p ) exist the following relationships:

[0016]

[0017] In the formula, ρ0 and c are the medium density and the sound velocity respectively, and [T] is a transfer matrix.

[0018] In the case that the airflow parameters and the cross-sectional area of the inlet and outlet sections of the perforated tube are consistent, the transmission loss TL of the perforated tube is:

[0019]

[0020] The values of the elements of the transfer matrix [T] are represented as:

[0021]

[0022] In the formula, [R] is a 4×4 square matrix, that is, l c1 and l c2 represent the axial lengths of the unperforated parts at both ends of the muffler; k=ωc is the wave number, ω=2πf is the angular frequency, and f represents the frequency; is an imaginary unit;

[0023] The square matrix [R] is transformed by another 4×4 operator square matrix [Q] and is represented as:

[0024] [R]=[Q(0)][Q(l p )] -1 (4);

[0025] The square matrix [Q(x)] is obtained by the following process:

[0026] For the shell or inner tube, its inner layer, i.e. the perforated wall, divides it into two parts, i.e. a perforated tube and an expansion cavity, and the sound pressure p1 inside the perforated tube and the sound pressure p2 inside the expansion cavity satisfy the following relationship:

[0027]

[0028] In the formula, D is a partial derivative operator; α1-α8 are coefficients, which are represented as follows:

[0029]

[0030]

[0031] In the formula, M1 and M2 represent the average gas flow Mach numbers in the perforated tube and the expansion cavity respectively; the inner diameter of the perforated tube is d p , the outer diameter of the perforated tube is d pe , and the outer diameter of the perforated shell is d r ; ξ is the average acoustic impedance ratio of the perforated tube, and for a perforated tube containing micro-holes and ordinary holes, it is obtained by parallel processing of the acoustic impedance ratios of the two sections as follows:

[0032]

[0033] In the formula, Q1 and Q2, and φ1 and φ2 represent the axial length proportion and the perforation ratio of the ordinary hole perforated section and the micro-hole perforated section respectively;

[0034] For the ordinary hole perforated section, the acoustic impedance ratio ξ1 under the action of the average flow is not considered in the transverse flow in the hole, and the formula is as follows:

[0035]

[0036] In the formula, μ is the dynamic viscosity of the fluid medium, t w is the wall thickness of the perforated tube, and d h1 is the diameter of the ordinary hole;

[0037] For the micro-hole perforated section, the acoustic impedance ratio ξ2 is as follows:

[0038]

[0039] In the formula, is the perforation constant; η is the viscosity coefficient of the medium; d h2 is the diameter of the micro-hole; J0 and J1 are the zero-order and first-order Bessel functions respectively; Q is a semi-empirical constant, which is 0.15; F γ is the influence coefficient of the gas flow on the acoustic resistance of the perforated tube, and is represented as follows:

[0040]

[0041] Equation (5) is a coupled equation, which needs to be decoupled by using a matrix eigenvalue decomposition method, and a coefficient matrix [B] is introduced:

[0042]

[0043] Eigenvalue decomposition of the matrix [B] can obtain four eigenvectors and four corresponding eigenvalues λ i , i = 1 ~ 4, let [Ψ] be a 4 × 4 matrix composed of the eigenvectors of the matrix [B], and obtain:

[0044]

[0045] After the theoretical model of the transmission loss of the perforated pipe is established by using the above process, the variables are optimized based on the genetic algorithm to maximize the transmission loss, and the average transmission loss in the calculation frequency range is defined as the fitness function obj:

[0046]

[0047] In the formula: x is the row vector of the independent variable of the objective function; f1 and f2 are the lower limit and upper limit of the calculation frequency; and Δf is the calculation frequency step;

[0048] The variables include the micro-hole diameter d h1 and the ordinary hole diameter d h2 , the perforation rate of the ordinary hole φ1 and the perforation rate of the micro-hole φ2, the thickness t w and the length l p of the perforated pipe, and the constraint conditions of each variable are as follows: 0.1 mm ≤ d h1 ≤ 1 mm, 1 mm ≤ d h2 ≤ 5 mm, 0.001 ≤ φ1, φ2 ≤ 0.15, t w and l p According to the space size and processing capacity on site.

[0049] The design method of the baffle plate is specifically:

[0050] At the highest noise reduction frequency f max , the corresponding maximum circular pipe inner diameter R max is inversely solved from the plane wave cut-off frequency formula of the circular cross-section pipe:

[0051]

[0052] When designing the baffle plate, each ring-shaped sector sub-cavity is regarded as a circular pipe with the same size, the equivalent radius of the circular pipe is determined according to the area consistency principle, and it is ensured that the equivalent radius and the radius of the inner perforated pipe do not exceed the maximum circular pipe inner diameter R max .

[0053] The beneficial effects of the present application are:

[0054] The application is based on a pipeline high-frequency muffler of sound mode modulation and perforated pipe, uses a partition to change the cavity structure in the pipe, modulates the high-order sound mode in the original pipe into a plane wave in the sub-channel, and uses a combination hole of micro holes and ordinary holes to effectively reduce the pipeline high-frequency pneumatic noise and realize the suppression of the high-frequency noise in the pipe. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 is a structure diagram of the pipeline high-frequency muffler of sound mode modulation and perforated pipe of the application;

[0056] Figure 2 is a sectional view of the pipeline high-frequency muffler of sound mode modulation and perforated pipe of the application;

[0057] Figure 3 is a sectional view of the partition of the pipeline high-frequency muffler of sound mode modulation and perforated pipe of the application;

[0058] Figure 4 is a plane structure diagram of the shell and the inner pipe of the pipeline high-frequency muffler of sound mode modulation and perforated pipe of the application.

[0059] In the figure: 101, shell; 102, inner pipe; 103, partition; 104, flange. DETAILED DESCRIPTION

[0060] The application will be described in detail below in combination with the drawings and specific embodiments.

[0061] The application is based on a pipeline high-frequency muffler of sound mode modulation and perforated pipe, as shown in Figure 1 , which comprises a shell 101, a cylindrical inner pipe 102 connected inside the shell 101 through a plurality of partitions 103; the plurality of partitions 103 are axially parallel to the inner pipe 102 and are uniformly arranged along the circumference of the inner pipe 102, and the plurality of partitions 103 divide the annular cavity formed between the shell 101 and the inner pipe 102 into a plurality of sub-cavities of the same size; the shell 101 is connected with flanges 104 at both ends, and the flanges 104 are arranged to facilitate the connection and disassembly of the muffler and the pipeline.

[0062] As shown in Figure 2 , the shell 101 is a double-layer structure, and the diameter of the contact part of the shell 101 and the partition 103 is larger than the diameter of both ends, so as to ensure that the flow area of the fluid flowing through the muffler is unchanged, as shown in Figure 4As shown, the inner and outer layers of the outer shell 101 maintain a certain distance. The inner layer of the outer shell 101 is perforated, specifically by dividing it into two sections along the vertical axial direction. One section has a number of micropores evenly distributed, and the other section has a number of ordinary holes evenly distributed. The micropores and ordinary holes are evenly distributed. The diameter of the micropores ranges from 0.1 mm to 1 mm, and the diameter of the ordinary holes ranges from 1 mm to 5 mm. The perforation rate of both micropores and ordinary holes is 0.1% to 15%. The inner layer perforation is used to reduce high-frequency noise in the pipeline. The advantage of combined holes compared to single holes is that they can achieve better bandwidth performance.

[0063] The inner tube 102 is a double-layered cylindrical structure, employing an airfoil-like structure with a rounded front and pointed rear. Its inner layer uses the same perforation treatment as the inner layer of the outer shell 101. When fluid passes through abrupt changes in the pipe, some energy is converted into heat or other forms of energy, resulting in energy loss. Simultaneously, a series of vortices are formed at the abrupt changes. These vortices interact during flow, generating secondary noise. The streamlined design of the inner tube 102 is intended to reduce flow loss at abrupt changes and avoid secondary noise generation.

[0064] The partition 103 is a rectangular metal plate used to connect the inner layer of the outer shell 101 and the outer layer of the inner tube 102, such as... Figure 3 As shown. The length of the partition 103 is equal to the length of the inner perforated portion of the inner tube 102, and the number is at least three, specifically determined by the target noise reduction frequency band and the pipe noise cutoff frequency. In the high-frequency range, the original pipe contains multiple higher-order acoustic modes. The partitions 103 are evenly distributed circumferentially along the inner tube 102, and the cavity inside the outer shell 101 is divided into multiple sub-cavities, including a central cavity and multiple peripheral cavities. The cross-sectional area of ​​the sub-cavities is smaller than that of the original cavity, and the cutoff frequency is larger. When the high-frequency noise in the target frequency band passes through the sub-cavities, it is all plane waves, thereby improving the noise reduction effect of the perforated pipe and achieving effective suppression of noise in a specific high-frequency band.

[0065] The perforation design method for the inner layer of the outer shell 101 and / or the inner layer of the inner tube 102 is designed with transmission loss as the indicator, specifically as follows:

[0066] For length l p The perforated tube, the sound pressure p1(0) at the inlet x=0, the sound particle velocity u1(0), and the outlet x=l p The sound pressure at p1(l) p Acoustic particle velocity u1(l) p The following relationship exists:

[0067]

[0068] In the formula, ρ0 and c are the medium density and sound velocity, respectively, and [T] is the transfer matrix;

[0069] In the case of the same cross-sectional area and the same gas flow parameter at the inlet and outlet of the perforated pipe, the transmission loss TL of the perforated pipe is:

[0070]

[0071] The values of the elements of the transfer matrix [T] are expressed as:

[0072]

[0073] where [R] is a 4x4 matrix, i.e. l c1 and l c2 represent the axial length of the unperforated part at the two ends of the muffler, respectively; k = ωc is the wave number, ω = 2πf is the angular frequency, and f represents the frequency; is the imaginary unit;

[0074] The square matrix [R] is obtained by transformation of another 4x4 operator matrix [Q] and is expressed as:

[0075] [R] = [Q(0)][Q(l p )] -1 (4);

[0076] The square matrix [Q(x)] is obtained by the following process:

[0077] For the shell 101 or the inner pipe 102, the inner layer, i.e., the perforated wall, divides it into a perforated pipe and an expansion cavity. By coupling the continuity equation, the momentum equation, and the isentropic relation inside the perforated pipe and the expansion cavity, the sound pressure p1 inside the perforated pipe and the sound pressure p2 inside the expansion cavity satisfy the following relations:

[0078]

[0079] where D is a partial derivative operator; α1-α8 are coefficients and are expressed as follows:

[0080]

[0081]

[0082] where M1 and M2 represent the average gas flow Mach numbers in the perforated pipe and the expansion cavity, respectively; the inner diameter of the perforated pipe is d p , the outer diameter of the perforated pipe is d pe , and the outer diameter of the perforated shell is d r ; ξ is the average acoustic impedance ratio of the perforated pipe, and for a perforated pipe containing micro-holes and ordinary holes, it is obtained by parallel processing of the acoustic impedance ratios of the two sections:

[0083]

[0084] In the formula, Q1 and Q2, φ1 and φ2 respectively represent the axial length ratio of the common hole perforation section and the micro-hole perforation section, and the perforation rate;

[0085] For the common hole perforation section, the acoustic impedance rate ξ1 under the average flow action is not considered in the hole transverse flow, and the formula is:

[0086]

[0087] In the formula, μ is the dynamic viscosity of the fluid medium, t w is the perforated pipe wall thickness, d h1 is the common hole diameter;

[0088] For the micro-hole perforation section, the acoustic impedance rate ξ2 formula is:

[0089]

[0090] In the formula, is the perforation constant; η is the viscosity coefficient of the medium; d h2 is the micro-hole diameter; J0 and J1 are the zero-order and first-order Bessel functions, respectively; Q is a semi-empirical constant, which is 0.15; F γ is the influence coefficient of gas flow on the acoustic resistance of the perforated pipe, which is expressed as:

[0091]

[0092] Equation (5) is a coupled equation, which needs to be decoupled by using the matrix eigenvalue decomposition method, and the coefficient matrix [B] is introduced:

[0093]

[0094] The matrix [B] is subjected to eigenvalue decomposition, and four characteristic vectors and corresponding four eigenvalues λ i , i = 1 ~ 4, let be a 4 × 4 matrix composed of the characteristic vectors of the matrix [B], and the following is obtained:

[0095]

[0096] After the above process establishes the theoretical model of the transmission loss of the perforated pipe, the genetic algorithm is used to optimize the variables to maximize the transmission loss, and the average transmission loss in the calculation frequency range is defined as the fitness function obj:

[0097]

[0098] In the formula, x is the row vector of the independent variable of the objective function; f1 and f2 are the lower limit and upper limit of the calculation frequency; and Δf is the calculation frequency step;

[0099] The optimization variables include six variables, specifically, the micro-hole diameter d h1 and the common-hole diameter d h2 , the common-hole perforation rate φ1 and the micro-hole perforation rate φ2, the perforation tube thickness t w and the length l p , and the constraint conditions of each variable are as follows: 0.1mm≤d h1 ≤1mm, 1mm≤d h2 ≤5mm, 0.001≤φ1, φ2≤0.15, t w and l p are determined according to the field space size and processing capacity.

[0100] The design method of the baffle 103 is specifically as follows:

[0101] At the highest noise reduction frequency f max , the corresponding maximum circular tube inner diameter R max is inversely calculated from the plane wave cutoff frequency formula of the circular cross-section tube:

[0102]

[0103] When designing the baffle, each ring-shaped fan-shaped sub-cavity is regarded as a circular tube with the same size, the equivalent radius of the circular tube is determined according to the area consistency principle, and it is ensured that the equivalent radius and the inner perforation tube radius are both not more than the maximum circular tube inner diameter R max .

[0104] Embodiment 1

[0105] This embodiment provides a pipeline high-frequency muffler based on acoustic mode modulation and perforation tubes, as shown in Figures 1-4 , the shell 101 is connected with a cylindrical inner tube 102 inside the shell 101 through a plurality of baffles 103; the plurality of baffles 103 are axially parallel to the inner tube 102 and are uniformly arranged along the circumference of the inner tube 102, and the plurality of baffles 103 divide the annular cavity formed between the shell 101 and the inner tube 102 into a plurality of sub-cavities with the same size; the shell 101 is connected with flanges 104 at both ends.

[0106] Embodiment 2

[0107] On the basis of embodiment 1, the shell 101 is a double-layer structure; the diameter of the contact part of the shell 101 and the baffle 103 is greater than the diameter of the two ends of the shell 101. The inner tube 102 is a double-layer cylindrical structure, which is a wing-shaped imitation with “front circle and rear sharp”; the inner layer of the shell 101 and the inner layer of the inner tube 102 are divided into two regions in the axial direction, a plurality of micro-holes are uniformly arranged in one region, and a plurality of common holes are uniformly arranged in the other region; the micro-holes and the common holes are uniformly distributed. The diameter of the micro-hole ranges from 0.1mm to 1mm, and the diameter of the common hole ranges from 1mm to 5mm; the perforation rates of the micro-hole and the common hole are both 0.1% to 15%.

[0108] Embodiment 3

[0109] On the basis of Embodiment 2, the partition plate 103 is a rectangular metal plate connecting the inner layer of the shell 101 and the outer layer of the inner tube 102. The number of the partition plate 103 is at least 3, and the length of the partition plate 103 is equal to the length of the perforated portion of the inner layer of the inner tube 102.

[0110] Embodiment 4

[0111] This embodiment provides a design method of a pipe high-frequency muffler based on acoustic mode modulation and perforated tube, including a perforation design method of the inner layer of the shell 101 and / or the inner layer of the inner tube 102 and a design method of the partition plate 103.

[0112] Embodiment 5

[0113] On the basis of Embodiment 4, the perforation design method of the inner layer of the shell 101 and / or the inner layer of the inner tube 102 is designed with transmission loss as an index, specifically:

[0114] For a perforated tube with a length of l p , the sound pressure p1(0) at the inlet x=0, the sound particle velocity u1(0) and the sound pressure p1(l p ) at the outlet x=l p , and the sound particle velocity u1(l p ) exist the following relationships:

[0115]

[0116] In the formula, ρ0 and c are the medium density and sound velocity respectively, and [T] is the transmission matrix.

[0117] In the case that the airflow parameters and cross-sectional areas of the inlet and outlet sections of the perforated tube are consistent, the transmission loss TL of the perforated tube is:

[0118]

[0119] The values of each element of the transmission matrix [T] are expressed as:

[0120]

[0121] In the formula, [R] is a 4×4 square matrix, that is, l c1 and l c2 represent the axial lengths of the unperforated portions at both ends of the muffler respectively; k=ωc is the wave number, ω=2πf is the angular frequency, and f represents the frequency; is the imaginary unit;

[0122] The square matrix [R] is transformed by another 4×4 operator square matrix [Q] and is expressed as:

[0123] [R] = [Q(0)] [Q(1 p )] -1 (4);

[0124] The square matrix [Q(x)] is obtained by the following process:

[0125] For the shell 101 or the inner tube 102, its inner layer, i.e., the perforated wall, divides it into two parts, a perforated tube and an expansion cavity, and the sound pressure p1 inside the perforated tube and the sound pressure p2 inside the expansion cavity satisfy the following relationship:

[0126]

[0127] In the formula, D is a partial derivative operator; α1-α8 are coefficients, which are represented as follows:

[0128]

[0129]

[0130] In the formula, M1 and M2 represent the average airflow Mach numbers in the perforated tube and the expansion cavity, respectively; the inner diameter of the perforated tube is d p , the outer diameter of the perforated tube is d pe , and the outer diameter of the perforated shell is d r ; ξ is the average acoustic impedance ratio of the perforated tube, and for a perforated tube containing micro-holes and ordinary holes, it is obtained by parallel processing of the acoustic impedance ratios of the two sections:

[0131]

[0132] In the formula: Q1 and Q2, φ1 and φ2 represent the axial length proportion and the perforation rate of the ordinary hole perforated section and the micro-hole perforated section, respectively;

[0133] For the ordinary hole perforated section, the acoustic impedance ratio ξ1 under the action of the average flow is not considered in the hole transverse flow, and the formula is:

[0134]

[0135] In the formula, μ is the dynamic viscosity of the fluid medium, t w is the perforated tube wall thickness, and d h1 is the ordinary hole diameter;

[0136] For the micro-hole perforated section, the acoustic impedance ratio ξ2 formula is:

[0137]

[0138] In the formula, is the perforation constant; η is the viscosity coefficient of the medium; d h2is the micro-hole diameter; J0and J1are zero-order and first-order Bessel functions, respectively; Q is a semi-empirical constant, and is 0.15; F γ is the influence coefficient of gas flow on the acoustic reactance of the perforated pipe, expressed as:

[0139]

[0140] Equation (5) is a coupled equation, and needs to be decoupled by using a matrix eigenvalue decomposition method. A coefficient matrix [B] is introduced:

[0141]

[0142] Eigenvalue decomposition is performed on the matrix [B], and four eigenvectors and corresponding four eigenvalues λ i , i = 1 ~ 4, let [Ψ] be a 4 × 4 matrix composed of the eigenvectors of the matrix [B], and obtain:

[0143]

[0144] After the theoretical model of the perforated pipe transmission loss is established by using the above process, the variables are optimized based on the genetic algorithm to maximize the transmission loss, and the average transmission loss in the calculation frequency range is defined as the fitness function obj:

[0145]

[0146] In the formula: x is the row vector of the independent variable of the objective function; f1and f2are the lower limit and upper limit of the calculation frequency; and Δf is the calculation frequency step;

[0147] The variables include the micro-hole diameter d h1 and the ordinary hole diameter d h2 , the ordinary hole perforation rate φ1and the micro-hole perforation rate φ2, the perforated pipe thickness t w and the length l p ; the constraint conditions of each variable are as follows: 0.1 mm ≤ d h1 ≤ 1 mm, 1 mm ≤ d h2 ≤ 5 mm, 0.001 ≤ φ1, φ2≤ 0.15, t w and l p are determined according to the space size and processing capacity on site.

[0148] Example 6

[0149] On the basis of Example 5, the design method of the baffle 103 is specifically:

[0150] At the highest noise reduction frequency f max , the corresponding maximum circular pipe inner diameter R max is inversely solved from the plane wave cut-off frequency formula of the circular cross-section pipe:

[0151]

[0152] When designing the baffle, each ring-fan sub-cavity is regarded as a circular tube with the same size, the equivalent radius of the circular tube is determined according to the principle of consistent area, and it is ensured that the equivalent radius and the radius of the inner perforated tube are both not more than the maximum inner diameter R of the circular tube max .

Claims

1. A high-frequency silencer for pipelines based on acoustic mode modulation and perforated pipes, characterized in that, The device includes an outer shell (101), inside which a cylindrical inner tube (102) is connected by a plurality of partitions (103); the plurality of partitions (103) are axially parallel to the inner tube (102) and uniformly arranged along the circumference of the inner tube (102); the plurality of partitions (103) divide the annular cavity formed between the outer shell (101) and the inner tube (102) into a plurality of sub-cavities of the same size; flanges (104) are connected to both ends of the outer shell (101); The outer shell (101) has a double-layer structure; the inner tube (102) has a double-layer cylindrical structure, which is an wing-shaped structure with a "round front and pointed back"; the inner layer of the outer shell (101) and the inner layer of the inner tube (102) are both divided into two regions in the vertical axial direction, one region is evenly distributed with a number of micropores, and the other region is evenly distributed with a number of ordinary pores; the micropores and ordinary pores are evenly distributed. The pore size of the micropores ranges from 0.1 mm to 1 mm, and the pore size of the ordinary pores ranges from 1 mm to 5 mm; the perforation rate of both the micropores and the ordinary pores is 0.1% to 15%.

2. The high-frequency silencer for pipelines based on acoustic mode modulation and perforated pipes according to claim 1, characterized in that, The diameter of the contact portion between the outer shell (101) and the partition (103) is greater than the diameter of both ends of the outer shell (101).

3. The high-frequency silencer for pipelines based on acoustic mode modulation and perforated pipes according to claim 1, characterized in that, The partition (103) is a rectangular metal plate that connects the inner layer of the outer shell (101) and the outer layer of the inner tube (102).

4. The high-frequency silencer for pipelines based on acoustic mode modulation and perforated pipes according to claim 1, characterized in that, The number of partitions (103) is at least three, and the length of the partitions (103) is equal to the length of the perforated portion of the inner tube (102).

5. The design method for a high-frequency silencer for a pipeline based on acoustic mode modulation and perforated pipe as described in any one of claims 1 to 4, characterized in that, The perforation design method includes the inner layer of the outer shell (101) and / or the inner layer of the inner tube (102) and the design method of the partition (103).

6. The design method for a high-frequency silencer for a pipeline based on acoustic mode modulation and perforated pipe according to claim 5, characterized in that, The perforation design method for the inner layer of the outer shell (101) and / or the inner layer of the inner tube (102) is designed with transmission loss as the indicator, specifically as follows: For length of Perforated tube, imported sound pressure at the location Acoustic particle velocity and exports sound pressure at the location Acoustic particle velocity The following relationship exists: （1） In the formula, and These are the density of the medium and the speed of sound, respectively. For the transfer matrix; When the airflow parameters and cross-sectional area of ​​the perforated pipe inlet and outlet are the same, the transmission loss TL of the perforated pipe is: （2） Transfer matrix The values ​​of each element are represented as follows: （3） In the formula, for phalanx; and These represent the axial lengths of the unperforated portions at both ends of the muffler; For wave number, Angular frequency, Indicates frequency; The imaginary unit; phalanx By another Operator matrix The transformation yields the following, represented as: （4） phalanx It is obtained through the following process: For the outer shell (101) or inner tube (102), its inner layer, namely the perforated wall, divides it into two parts: the perforated tube and the expansion cavity. The sound pressure inside the perforated tube... and the sound pressure inside the expansion cavity The following relationship must be satisfied: （5） In the formula, For partial derivative operators; The coefficient is represented as follows: （6） （7） （8） （9） （10） （11） （12） （13） In the formula, and These represent the average Mach numbers of the airflow inside the perforated tube and the expansion chamber, respectively; the inner diameter of the perforated tube is... The outer diameter of the perforated tube is The outer diameter of the perforated outer shell is ; The average acoustic impedance of the perforated tube is obtained by paralleling the acoustic impedance of the two segments, for a perforated tube containing both micropores and ordinary pores: （14） In the formula: and , and These represent the axial length ratio and perforation rate of the perforated section for ordinary holes and the perforated section for micro holes, respectively. For a typical perforated section, neglecting transverse flow within the hole, the acoustic impedance under average flow conditions is... The formula is: （15） In the formula, The dynamic viscosity of the fluid medium. For the thickness of the perforated pipe wall, For ordinary hole diameter; For the micro-perforated section, acoustic impedance The formula is: （16） In the formula, The perforation constant; The viscosity coefficient of the medium; Micropore diameter; and These are the zeroth-order and first-order Bessel functions, respectively. This is a semi-empirical constant, taken as 0.15; The effect coefficient of gas flow on the acoustic impedance of the perforated pipe is expressed as: （17） Equation (5) is a coupled equation, and the matrix eigenvalue decomposition method is needed to decouple the system of equations. A coefficient matrix is ​​introduced. : （18） For matrix Eigenvalue decomposition yields four eigenvectors and their corresponding four eigenvalues. ,make For matrix The eigenvectors formed by Square matrix, resulting in: （19） After establishing the theoretical model of perforated pipe transmission loss using the above process, the genetic algorithm is used to optimize the variables to maximize the transmission loss. The average transmission loss within the calculation frequency range is defined as the fitness function obj. （20） In the formula: Let be the row vector of the independent variables of the objective function; and To calculate the lower and upper limits of the frequency; To calculate the frequency step size; The variables include micropore size. Ordinary hole diameter Ordinary hole perforation rate and micropore perforation rate Perforated tube thickness and length The constraints for each variable are as follows: , , , and Determined based on site space dimensions and processing capacity.

7. The design method for a high-frequency silencer for a pipeline based on acoustic mode modulation and perforated pipe according to claim 6, characterized in that, The design method of the partition (103) is as follows: At the highest noise reduction frequency Below, the maximum inner diameter of the circular pipe is calculated by inversely using the formula for the cutoff frequency of a plane wave in a circular cross-section pipe. : （21） When designing the partition, each annular sector sub-cavity is treated as a circular tube of the same size. The equivalent radius of the circular tube is determined according to the principle of consistent area, ensuring that both the equivalent radius and the radius of the inner perforated tube do not exceed the inner diameter of the maximum circular tube. .

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