A method for predicting acoustic characteristics of irregular multi-cavity perforated muffler under flow conditions

Abstract

The present invention relates to a method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions, the method comprising the following steps: S1, establishing a three-dimensional flow sound field model for the muffler under flow conditions, and constructing acoustic finite element equations of different subdomains inside the muffler; S2, establishing a perforated acoustic impedance model considering non-uniform flow; S3, solving the acoustic finite element equations of different subdomains to obtain corresponding transverse modes; S4, constructing an acoustic continuity equation group using a modal matching method, solving the equation group under different outlet boundaries to obtain transfer matrices of different muffler units, and solving the transfer matrix to obtain the overall acoustic characteristics of the muffler. Compared with the prior art, the present invention fully considers the microscopic flow characteristics, has accurate prediction results, and has high calculation efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of industrial noise reduction, and in particular to a method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions. Background Art

[0002] In recent years, people have paid more and more attention to ride comfort. Car noise has a direct impact on the subjective feelings of passengers. Improving ride comfort is bound to achieve the attenuation control of the noise when the vehicle is driving. In order to ensure both power and economy, new power vehicles have begun to generally use turbochargers to achieve this goal. However, the power output of electric vehicles or hydrogen fuel cell vehicles does not generate much noise, resulting in the noise of the supercharged intake system becoming a new noise source. Therefore, how to achieve noise control of the supercharged intake system has become a topic that needs to be studied urgently.

[0003] Judging from the current public literature and related information, the current focus of domestic and foreign research is on the prediction of the acoustic characteristics of regular cross-section mufflers under flow conditions. The research on the prediction method of the acoustic characteristics of irregular cross-section mufflers that adapt to narrow installation spaces is not sufficient. Traditional prediction methods such as the transfer matrix method based on plane waves, the three-dimensional analytical method based on the direct integration method, modal matching method or the point matching method cannot solve the mufflers of irregular cross-section types. Although the acoustic finite element simulation method can solve the acoustic characteristics of mufflers of arbitrary structures, the calculation cost is high and the accuracy is greatly limited by the grid.

[0004] In order to effectively control the noise in the supercharged intake system, considering the narrow space and high-speed airflow in the supercharged intake duct, and reducing the development time and cost of the muffler, it is necessary to propose an acoustic characteristic prediction theory and a muffler structural optimization method for an irregular multi-cavity perforated muffler considering high-speed airflow on the basis of existing theories, and apply them to the design of a muffler with good sound absorption performance, low pressure loss and compact structure for noise reduction in the supercharged intake system. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for predicting the acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions, the method comprising the following steps:

[0008] S1. A three-dimensional sound field model with flow is established for the muffler under flow conditions, and acoustic finite element equations of different subdomains inside the muffler are constructed;

[0009] S2. Establish a perforation acoustic impedance model considering non-uniform flow;

[0010] S3, solving the acoustic finite element equations of different subdomains to obtain the corresponding transverse modes;

[0011] S4. Use the modal matching method to construct the acoustic continuity equation group, solve the equation group under different outlet boundaries to obtain the transfer matrix of different silencer units, and obtain the overall acoustic characteristics of the silencer by solving the transfer matrix.

[0012] Preferably, the different sub-areas inside the muffler in step S1 include the inside of the muffler perforated tube, the inside of the muffler cavity, the inlet and outlet pipes of the muffler, and the annular cavity of the muffler.

[0013] Preferably, the acoustic finite element equation inside the perforated tube of the muffler is:

[0014]

[0015] Where [K1] is the overall stiffness matrix of the perforated pipe, k = ω / c = 2πf / c, k is the acoustic wave number, f is the acoustic frequency, c is the speed of sound, M is the Mach number of the airflow in the perforated pipe, and k z is the axial wave number of the acoustic pressure, [M1] is the overall mass matrix of the pipe in the perforated pipe, j is the imaginary unit, ζ p is the acoustic impedance of the perforated plate, [Z 11 ] is the overall impedance matrix of the envelope area in the perforated tube, [Z 12 ] is the overall impedance matrix of the outer envelope area of ​​the perforated tube, p xy1 is the lateral sound pressure component of the pipe in the perforated pipe, p xy2 is the lateral sound pressure component of the expansion cavity containing the perforated tube.

[0016] Preferably, the acoustic finite element equation inside the muffler cavity is:

[0017]

[0018] where [K2] is the overall stiffness matrix of the expansion cavity containing the perforated tube, k xy2 is the transverse wave number of the expansion cavity containing the perforated tube, [M2] is the overall mass matrix of the expansion cavity containing the perforated tube, j is an imaginary unit, k is the acoustic wave number, ζ p is the acoustic impedance of the perforated plate, [Z 11 ] is the overall impedance matrix of the envelope area in the perforated tube, [Z 12 ] is the overall impedance matrix of the outer envelope area of ​​the perforated tube, p xy1 is the lateral sound pressure component of the pipe in the perforated pipe, p xy2 is the lateral sound pressure component of the expansion cavity containing the perforated tube.

[0019] Preferably, the acoustic finite element equation of the muffler inlet and outlet pipes is:

[0020]

[0021] Where [K1] is the overall stiffness matrix of the pipe in the perforated pipe, [M1] is the overall mass matrix of the pipe in the perforated pipe, and k xy1 is the transverse wave number of the pipe in the perforated pipe, p xy1 is the lateral sound pressure component of the pipe inside the perforated pipe.

[0022] Preferably, the acoustic finite element equation of the muffler annular cavity is:

[0023]

[0024] Where [K2] is the overall stiffness matrix of the expansion cavity containing the perforated tube, [M2] is the overall mass matrix of the expansion cavity containing the perforated tube, and k xy2 is the transverse wave number of the expansion cavity containing the perforated tube, p xy2 is the lateral sound pressure component of the expansion cavity containing the perforated tube.

[0025] Preferably, step S2 specifically includes: using the theory of perforation acoustic impedance and simulation calculation to fit the variation law of the partial acoustic impedance generated by the flow, and then obtaining a perforation acoustic impedance model considering the non-uniform flow.

[0026] Preferably, the variation law of the partial acoustic impedance generated by the flow obtained by fitting in step S2 is expressed as:

[0027]

[0028]

[0029] Among them, r f is the acoustic resistance caused by flow, x f is the acoustic reactance caused by flow, S t is the Strouhal number. Preferably, the perforation acoustic impedance model considering the non-uniform flow in step S2 is expressed as:

[0030] r h =r n +M c r f

[0031] x h =x n +kd h x f

[0032] Among them, r h is the acoustic resistance of the perforated part, xh is the acoustic impedance of the perforated part, r n is the acoustic resistance of the hole without flow, x n is the perforation acoustic reactance in the absence of flow, M c is the Mach number of the flow at the small hole, and k=2πf / c is the wave number.

[0033] Preferably, in step S4, different outlet boundary conditions are assumed to obtain the acoustic characteristics of each single cavity of the multi-cavity perforated muffler, and then the overall acoustic characteristics are quickly calculated.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] (1) The present invention combines the advantages of numerical simulation method and three-dimensional analytical method, and can solve the acoustic characteristics of perforated mufflers of arbitrary cross-sectional shapes while ensuring calculation efficiency;

[0036] (2) The present invention obtains a perforation acoustic impedance model taking into account microscopic flow based on perforation acoustic impedance and CFD simulation calculation, and applies it to the prediction method;

[0037] (3) The present invention combines the two-dimensional transfer matrix method to unitize the complex boundary conditions inside the multi-cavity perforated muffler to improve the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A flowchart of a method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to the present invention;

[0039] Figure 2 A technical roadmap of a method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to the present invention;

[0040] Figure 3 It is a schematic diagram of the irregular cross section and acoustic domain division of the perforated muffler of the present invention;

[0041] Figure 4 This is an experimental verification diagram of a method for predicting the acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to the present invention. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Note that the following embodiments are merely illustrative in nature, and the present invention is not intended to limit its applicable objects or uses, and the present invention is not limited to the following embodiments.

[0043] Example

[0044] Combination Figure 1 , Figure 2This embodiment provides a method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions, the method comprising the following steps:

[0045] S1. A three-dimensional sound field model with flow is established for the muffler under flow conditions, and acoustic finite element equations of different subdomains inside the muffler are constructed;

[0046] S2. Establish a perforation acoustic impedance model considering non-uniform flow;

[0047] S3, solving the acoustic finite element equations of different subdomains to obtain the corresponding transverse modes;

[0048] S4. Use the modal matching method to construct the acoustic continuity equation group, solve the equation group under different outlet boundaries to obtain the transfer matrix of different silencer units, and obtain the overall acoustic characteristics of the silencer by solving the transfer matrix.

[0049] The cross section and internal acoustic domain division of the irregular cross-section multi-cavity perforated muffler are as follows: Figure 3 As shown in the figure, S1 is the acoustic domain of the perforated pipe cross section, S2 is the acoustic domain of the expansion cavity of the perforated pipe, L1 and L2 are the inner and outer envelopes of the perforated pipe, respectively, the direction along the perforated pipe is the z-axis, the muffler cross section is the xy plane, A and E are the straight pipe units of the inlet and outlet pipes of the muffler, B and D are the annular cavity units inside the muffler, C1 is the inner pipe of the perforated pipe, C2 is the expansion cavity containing the perforated pipe part, l i , l o are the lengths of the annular cavity B and D respectively, l m The length of the perforated part.

[0050] The different sub-domains inside the muffler in step S1 include the inside of the muffler perforated pipe, the inside of the muffler cavity, the inlet and outlet pipes of the muffler, and the annular cavity of the muffler.

[0051] The acoustic finite element equation for establishing the discrete unit of the muffler cross section is as follows:

[0052]

[0053] in, is the Laplace operator, S is the integral surface of the discrete cross section, ω = 2πf is the angular frequency, j is the imaginary unit, and u n is the particle vibration velocity, and L is the integration domain after the perforated tube envelope is discretized.

[0054] The sound pressure at any node after the cross-sectional acoustic domain is discretized is:

[0055]

[0056] The governing equation for sound pressure is:

[0057]

[0058] The muffler wall is rigid and the boundary conditions are:

[0059]

[0060] The normal acoustic pressure gradient on both sides of the perforated tube surface can be expressed as:

[0061]

[0062]

[0063] Combining the above boundary conditions, we can get:

[0064]

[0065] Furthermore, the acoustic finite element equation inside the perforated tube of the muffler is:

[0066]

[0067] Where [K1] is the overall stiffness matrix of the perforated pipe, k = ω / c = 2πf / c, k is the acoustic wave number, f is the acoustic frequency, c is the speed of sound, M is the Mach number of the airflow in the perforated pipe, and k z is the axial wave number of the acoustic pressure, [M1] is the overall mass matrix of the pipe in the perforated pipe, j is the imaginary unit, ζ p is the acoustic impedance of the perforated plate, [Z 11 ] is the overall impedance matrix of the envelope area in the perforated tube, [Z 12 ] is the overall impedance matrix of the outer envelope area of ​​the perforated tube, p xy1 is the lateral sound pressure component of the pipe in the perforated pipe, p xy2 is the lateral sound pressure component of the expansion cavity containing the perforated tube.

[0068] The acoustic finite element equation inside the muffler cavity is:

[0069]

[0070] where [K2] is the overall stiffness matrix of the expansion cavity containing the perforated tube, k xy2 is the transverse wave number of the expansion cavity containing the perforated tube, [M2] is the overall mass matrix of the expansion cavity containing the perforated tube, j is an imaginary unit, k is the acoustic wave number, ζ p is the acoustic impedance of the perforated plate, [Z 11 ] is the overall impedance matrix of the envelope area in the perforated tube, [Z 12 ] is the overall impedance matrix of the outer envelope area of ​​the perforated tube, p xy1 is the lateral sound pressure component of the pipe in the perforated pipe, p xy2is the lateral sound pressure component of the expansion cavity containing the perforated tube.

[0071] The acoustic finite element equation of the muffler inlet and outlet pipes is:

[0072]

[0073] Where [K1] is the overall stiffness matrix of the pipe in the perforated pipe, [M1] is the overall mass matrix of the pipe in the perforated pipe, and k xy1 is the transverse wave number of the pipe in the perforated pipe, p xy1 is the lateral sound pressure component of the pipe inside the perforated pipe.

[0074] The acoustic finite element equation of the muffler annular cavity is:

[0075]

[0076] Where [K2] is the overall stiffness matrix of the expansion cavity containing the perforated tube, [M2] is the overall mass matrix of the expansion cavity containing the perforated tube, and k xy2 is the transverse wave number of the expansion cavity containing the perforated tube, p xy2 is the lateral sound pressure component of the expansion cavity containing the perforated tube.

[0077] Step S2 specifically includes: using the theory of perforated acoustic impedance and CFD time-domain simulation calculation to fit the variation law of the partial acoustic impedance generated by the flow, and then obtaining a perforated acoustic impedance model that takes into account the non-uniform flow.

[0078] The calculation method of perforated acoustic impedance is:

[0079]

[0080]

[0081] in, It represents the incident acoustic impedance on one side of the perforated plate under flow conditions, which needs to be calculated by FLUENT simulation later. It indicates the acoustic impedance under no-flow conditions, which is only determined by the changes in structural parameters.

[0082] Based on this, the fitting result of the variation law of the partial acoustic impedance caused by the flow is expressed as:

[0083]

[0084]

[0085] Among them, r f is the acoustic resistance caused by flow, x f is the acoustic reactance caused by flow, S tis the Strouhal number. Furthermore, the perforated acoustic impedance model considering non-uniform flow is expressed as:

[0086] r h =r n +M c r f

[0087] x h =x n +kd h x f

[0088] Among them, r h is the acoustic resistance of the perforated part, x h is the acoustic impedance of the perforated part, r n is the acoustic resistance of the hole without flow, x n is the perforation acoustic reactance in the absence of flow, M c is the Mach number of the flow at the small hole, and k=2πf / c is the wave number.

[0089] In step S4, different outlet boundary conditions are assumed to obtain the acoustic characteristics of each single cavity of the multi-cavity perforated muffler, and then the overall acoustic characteristics are quickly calculated.

[0090] The two-dimensional transfer matrix method constructs different silencing units, specifically:

[0091] Design of fully reflective terminal:

[0092]

[0093] Designing non-reflective terminations:

[0094]

[0095] in, is the sound pressure amplitude coefficient of the incident wave or reflected wave in each acoustic domain.

[0096] The transfer matrix can be expressed as:

[0097]

[0098] To solve the transfer matrix T m11 、T m12 、T m21 、T m22 , it is necessary to construct a system of continuity equations based on the acoustic boundary conditions to solve the system of equations for the modal amplitude coefficients.

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105] In order to solve the modal amplitude coefficients of each acoustic domain, it is necessary to truncate the infinite-order mode to N-order and solve the above equations simultaneously. There are 6 (N+1) unknowns in the equations. These unknowns are the sound pressure amplitude coefficients of the incident wave or reflected wave in each acoustic domain. For the sake of simplicity, it is assumed that the inlet sound wave is a plane wave and the sound pressure amplitude is 1, that is, Assume that there is no reflection at the exit, that is The transmission loss can be obtained according to the following calculation formula:

[0106]

[0107] Among them, T 11 ,T 12 ,T 21 ,T 22 is the value of the corresponding position in the transfer matrix [T].

[0108] Based on this prediction method, a program is written to calculate the transmission loss of an irregular five-cavity perforated muffler. Figure 4 As shown in the figure, the experimental data and theoretical prediction data are in good agreement in the main anechoic frequency range, which verifies the accuracy of the prediction method.

[0109] The above embodiments are merely examples and do not limit the scope of the present invention. These embodiments can also be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the technical concept of the present invention.

Claims

1. A method for predicting the acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions, characterized in that: The method comprises the following steps: S1. A three-dimensional sound field model with flow is established for the muffler under flow conditions, and acoustic finite element equations of different subdomains inside the muffler are constructed; S2. Establish a perforation acoustic impedance model considering non-uniform flow; S3, solving the acoustic finite element equations of different subdomains to obtain the corresponding transverse modes; S4. Use the modal matching method to construct an acoustic continuity equation group, solve the equation group under different outlet boundaries to obtain the transfer matrix of different muffler units, and obtain the overall acoustic characteristics of the muffler by solving the transfer matrix; Step S2 specifically includes: using the theory of perforated acoustic impedance and simulation calculation to fit the variation law of the partial acoustic impedance generated by the flow, and then obtaining a perforated acoustic impedance model considering the non-uniform flow; The variation law of the partial acoustic impedance caused by the flow obtained by fitting in step S2 is expressed as: Among them, r f is the acoustic resistance caused by flow, x f is the acoustic reactance caused by flow, S t is the Strouhal number; The perforation acoustic impedance model considering non-uniform flow in step S2 is expressed as: r h ＝r n +M c r f x h =x n +kd h x f Among them, r h is the acoustic resistance of the perforated part, x h is the acoustic impedance of the perforated part, r n is the acoustic resistance of the hole without flow, x n M is the perforation acoustic reactance in the absence of flow. c is the Mach number of the flow at the small hole, and k=2πf / c is the wave number.

2. The method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to claim 1 is characterized in that: The different sub-domains inside the muffler in step S1 include the inside of the muffler perforated pipe, the inside of the muffler cavity, the inlet and outlet pipes of the muffler, and the annular cavity of the muffler.

3. The method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to claim 2 is characterized in that: The acoustic finite element equation inside the perforated tube of the muffler is: Where [K1] is the overall stiffness matrix of the perforated pipe, k = ω / c = 2πf / c, k is the acoustic wave number, f is the acoustic frequency, c is the speed of sound, M is the Mach number of the airflow in the perforated pipe, and k z is the axial wave number of the acoustic pressure, [M1] is the overall mass matrix of the pipe in the perforated pipe, j is the imaginary unit, ζ p is the acoustic impedance of the perforated plate, [Z 11 ] is the overall impedance matrix of the envelope area in the perforated tube, [Z 12 ] is the overall impedance matrix of the outer envelope area of ​​the perforated tube, p xy1 is the lateral sound pressure component of the pipe in the perforated pipe, p xy2 is the lateral sound pressure component of the expansion cavity containing the perforated tube.

4. The method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to claim 2 is characterized in that: The acoustic finite element equation inside the muffler cavity is: where [K2] is the global stiffness matrix of the expansion cavity containing the perforated tube, k xy2 is the transverse wave number of the expansion cavity containing the perforated tube, [M2] is the overall mass matrix of the expansion cavity containing the perforated tube, j is an imaginary unit, k is the acoustic wave number, ζ p is the acoustic impedance of the perforated plate, [Z 11 ] is the overall impedance matrix of the envelope area in the perforated tube, [Z 12 ] is the overall impedance matrix of the outer envelope area of ​​the perforated tube, p xy1 is the lateral sound pressure component of the pipe in the perforated pipe, p xy2 is the lateral sound pressure component of the expansion cavity containing the perforated tube.

5. The method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to claim 2 is characterized in that: The acoustic finite element equation of the muffler inlet and outlet pipes is: Where [K1] is the overall stiffness matrix of the pipe in the perforated pipe, [M1] is the overall mass matrix of the pipe in the perforated pipe, and k xy1 is the transverse wave number of the pipe in the perforated pipe, p xy1 is the lateral sound pressure component of the pipe inside the perforated pipe.

6. The method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to claim 2 is characterized in that: The acoustic finite element equation of the muffler annular cavity is: Where [K2] is the overall stiffness matrix of the expansion cavity containing the perforated tube, [M2] is the overall mass matrix of the expansion cavity containing the perforated tube, and k xy2 is the transverse wave number of the expansion cavity containing the perforated tube, p xy2 is the lateral sound pressure component of the expansion cavity containing the perforated tube.

7. The method for predicting acoustic characteristics of an irregular multi-cavity perforated muffler under flow conditions according to claim 1 is characterized in that: In step S4, different outlet boundary conditions are assumed to obtain the acoustic characteristics of each single cavity of the multi-cavity perforated muffler, and then the overall acoustic characteristics are quickly calculated.

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