A method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations

Abstract

The present application relates to a kind of construction methods based on embedded tube and different cavity deep configuration honeycomb type acoustic lining, honeycomb type acoustic lining multiple parallel honeycomb cavities, each honeycomb cavity is equipped with embedded tube, method specifically includes the transfer matrix model of each honeycomb cavity is constructed, to calculate the surface impedance of honeycomb type acoustic lining as a whole, by optimizing the embedded tube diameter of each honeycomb cavity, embedded tube length and the height of entire honeycomb cavity, so that the average sound absorption coefficient of honeycomb type acoustic lining as a whole reaches optimal in specific frequency band range.Compared with traditional honeycomb type acoustic lining, the acoustic lining constructed by the method of the present application has the advantages of being lighter and thinner, easy to process, good engineering application prospect and the like.

Description

Technical Field

[0001] This invention relates to the field of noise control technology, and in particular to a method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations. Background Technology

[0002] In recent years, aircraft engine noise has received increasing attention in the aviation field. Acoustic liners with good sound absorption properties are typically installed in the nacelle to suppress engine noise. With the rapid development of aviation technology, modern aviation has placed even more stringent demands on aircraft engine noise control. Achieving lower-frequency and wider-bandwidth noise control with a thinner and lighter acoustic liner configuration remains a significant challenge.

[0003] Porous and fibrous materials can achieve good broadband sound absorption at higher frequencies, but these materials often have a volume comparable to the operating wavelength. Low-frequency deficiencies and large size limit their practical application in acoustic liner design. Traditional single-degree-of-freedom and multi-degree-of-freedom acoustic liners are usually composed of perforated plates and honeycomb core chambers. These sound absorbers, dominated by resonance effects, can effectively improve the shortcomings of low-frequency sound absorption. Nayfeh et al.'s research on the sound absorption of a single-layer honeycomb core chamber combined with different cover plate materials showed that this configuration can achieve efficient sound absorption in the lower target frequency band. Xie et al. used a similar configuration to design single-layer sound-absorbing structures with different perforation diameters and explored the influence of pore size on absorption peaks. Sui's method of combining a membrane with a honeycomb back cavity achieved a sound insulation effect of 50dB below 500Hz. However, overall, the sound absorption bandwidth of the above structures is relatively narrow, which is very limiting in practical applications. Peng et al. achieved a sound absorption coefficient of 0.9 in the 600-1000Hz frequency band by adjusting the thickness of the perforated plate and the diameter of the perforation holes. At the same time, the researchers also tried to design sound absorption structures with inconsistent cavity depths, but the overall sound liner configuration was still relatively thick and heavy. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art by providing a method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations, which reduces the thickness of the acoustic liner and has a simple and easy-to-process overall structure.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for constructing a honeycomb acoustic liner based on embedded tubes and different cavity depth configurations, wherein the honeycomb acoustic liner comprises multiple parallel honeycomb cavities, each of which is provided with an embedded tube. The method includes constructing an acoustic liner with optimal sound absorption in a specific frequency band by optimizing the diameter and length of the embedded tubes in each honeycomb cavity and the height of the entire honeycomb cavity.

[0007] Furthermore, the method specifically includes constructing a transfer matrix model for each honeycomb cavity to calculate the overall surface impedance of the honeycomb acoustic liner. By optimizing the inner tube diameter, inner tube length, and overall height of the honeycomb cavity for each honeycomb cavity, the average sound absorption coefficient of the honeycomb acoustic liner is optimized within a specific frequency band.

[0008] Furthermore, through parallel coupling design, the diameter, length and height of each embedded tube in the overall honeycomb acoustic liner are designed to optimize the sound absorption coefficient of the overall honeycomb acoustic liner.

[0009] Furthermore, the expression for the transfer matrix model of each cellular cavity is as follows:

[0010]

[0011]

[0012]

[0013]

[0014]

[0015] In the formula, T is the transfer matrix model of a single cellular cavity, and M... c1 To account for the transfer matrix after correction of the tube end impedance, M C M is the transfer matrix of the air domain C in the embedded tube. B M is the transfer matrix of the air domain B surrounding the embedded tube. A Let be the transfer matrix of the air domain A below the embedded tube, j be the imaginary unit, k0 be the sound wavenumber in the air, δ1 be the impedance correction for the end of the embedded tube, Z0 be the characteristic impedance of the air medium, and S be the transfer matrix of the air domain A below the embedded tube. C k is the cross-sectional area of ​​the embedded tube. C Let l be the equivalent complex wavenumber in a cylindrical waveguide. i Z is the length of the embedded tube. C δc is the characteristic impedance of region C, δ2 is the impedance correction at the end of the cylindrical embedded tube inside the cavity, η is the dynamic viscosity of air, ω is the angular frequency, and k is the characteristic impedance of region C. B Let t be the equivalent complex wavenumber of medium in region B. a For the wall thickness of the honeycomb cavity, S B Let Z be the cross-sectional area of ​​region B. B Let k be the characteristic impedance of the dielectric in region B. A Let l be the equivalent complex wavenumber of medium in region A. A Let Z be the length of region A. A Let S be the characteristic impedance of the dielectric in region A. A Let be the cross-sectional area of ​​region A.

[0016] Furthermore, the expression for calculating the equivalent complex wavenumber of a hexagonal cavity is as follows:

[0017]

[0018]

[0019]

[0020] In the formula, k c Let c be the equivalent complex wavenumber of the hexagonal cavity, c0 be the static speed of sound in air, and H be the static velocity of sound in air. d The hydraulic diameter of the cavity cross-section is given by ρ0, air density is given by γ, heat capacity ratio is given by Pr, and C is given by C. p Where K is the constant pressure heat capacity and K is the thermal conductivity.

[0021] Furthermore, the expression for calculating the impedance of a single cellular cavity is as follows:

[0022] Z ai =T1 / T3

[0023] In the formula, Z ai The impedance of the i-th cell cavity;

[0024] The expression for calculating the surface impedance of the honeycomb acoustic liner as a whole is:

[0025]

[0026] In the formula, Z a The overall surface impedance of the honeycomb acoustic liner.

[0027] Furthermore, the expression for calculating the sound absorption coefficient is as follows:

[0028]

[0029] In the formula, α is the sound absorption coefficient, Z0 is the characteristic impedance of the propagation medium, and S is the incident area of ​​the sound wave.

[0030] Furthermore, the honeycomb cavity is a columnar structure with a hexagonal cross-section.

[0031] Furthermore, the embedded tube has a cylindrical structure.

[0032] Furthermore, each of the embedded tubes is fixed at the center of one end of the corresponding honeycomb cavity.

[0033] Furthermore, the diameter of the inner tube, the length of the inner tube, and the height of the entire honeycomb cavity of each of the aforementioned honeycomb cavity units are all variable and can be the same or different.

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

[0035] This invention adds an embedded tube structure to the traditional honeycomb acoustic liner and also considers the cavity depth of the honeycomb cavity as a designable parameter. Taking into account viscous loss and thermal loss, a theoretical model of the acoustic liner structure is constructed using the transfer matrix method. Based on this theoretical model, the influence of three designable structural parameters—the diameter and length of the embedded tube, and the cavity depth—on the sound absorption effect of the single-unit sound-absorbing structure is investigated.

[0036] Finally, considering the coupling effect between individual units, three acoustic liner structures with maximum thicknesses of 35mm, 45mm, and 51mm were designed, achieving low-frequency broadband sound absorption effects of 400-600Hz, 400-800Hz, and 600-1600Hz respectively. The average sound absorption coefficients all reached above 0.92, and the theoretical, simulation, and experimental results showed good agreement.

[0037] The embedded tube and cavity depth configurations provide greater freedom for acoustic liner design. Compared with traditional acoustic liner structures, the design of this invention is thinner and lighter. The collaborative design of multiple degrees of freedom and the consideration of the coupling effect between individual structures greatly reduce the thickness of the acoustic liner. The overall configuration is simple and easy to process, and it is expected to be applied in engineering fields such as noise reduction of aero-engines.

[0038] The acoustic liner configuration proposed in this study is lighter and thinner, easier to process, and has good prospects for engineering applications. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations provided in an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of a honeycomb cavity single-unit structure provided in an embodiment of the present invention;

[0041] Figure 3 This is a cross-sectional schematic diagram of a honeycomb cavity unit provided in an embodiment of the present invention. In the figure, incident wave is the incident wave.

[0042] Figure 4 The figure shows the experimental results of an MHREA monomer provided in an embodiment of the present invention. In the figure, (a) is the sound absorption curve of the MHREA monomer; (b) is the change of the sound absorption coefficient with the diameter d of the embedded tube (w s =15mm, l=3mm, L=24mm); (c) shows the change of sound absorption coefficient with the length l of the embedded tube (w s =15mm, d=20.4mm, L=24mm); (d) is the change of sound absorption coefficient with cavity depth L (w s=15mm, d=20.4mm, l=3mm);

[0043] Figure 5 The figure shows the experimental results of the sound absorption effect of a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations provided in the embodiments of the present invention. In the figure, (a) shows the overall structure of the acoustic liner and the sound absorption of each individual unit. The solid line represents the theoretical sound absorption effect of the overall structure, the asterisk represents the finite element simulation calculation result, the circle represents the experimental result, and the dashed line represents the sound absorption of each individual unit; (b) shows the impedance diagram of the acoustic liner, and the inset is the sample model; (c) shows the reflection characteristics of the acoustic liner on the complex frequency plane. The black solid circle represents the minimum and maximum values ​​of the sound absorption coefficient ln|r'|, i.e., the zero point and the pole, when the sound absorption coefficient is 0.9.

[0044] Figure 6 The figures show the experimental results of the sound absorption effect of two other honeycomb acoustic liners based on embedded tubes and different cavity depth configurations provided in the embodiments of the present invention. In the figures, (a) and (b) are the sound absorption coefficient curve and impedance curve of the acoustic liner with a maximum thickness of 45 mm, respectively; (c) and (d) are the sound absorption coefficient curve and impedance curve of the acoustic liner with a maximum thickness of 51 mm, respectively. The inset is a schematic diagram of the acoustic liner model.

[0045] In the figure, Resistance is impedance, Reactance is reactance, Theory is theoretical sound absorption effect, Simulation is finite element simulation calculation result, Experiment is experimental result, 1 is honeycomb cavity, 2 is embedded tube. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0048] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0049] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed during use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0050] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0051] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0052] Example 1

[0053] This embodiment provides a method for constructing a honeycomb acoustic liner based on embedded tubes and different cavity depth configurations. The honeycomb acoustic liner has multiple parallel honeycomb cavities, each of which is equipped with an embedded tube. The method includes constructing a theoretical model of the transfer matrix of each honeycomb cavity to calculate the overall surface impedance of the honeycomb acoustic liner. By optimizing the diameter and length of the embedded tubes of each honeycomb cavity and the height of the entire honeycomb cavity, the average sound absorption coefficient of the honeycomb acoustic liner is optimized within a specific frequency band.

[0054] This embodiment first establishes a model of a single honeycomb cavity and derives the following rules: reducing the diameter of the embedded tube will shift the absorption peak of the honeycomb acoustic liner to lower frequencies; increasing the length of the embedded tube will improve the low-frequency sound absorption effect; and changing the height of the entire honeycomb cavity will adjust the position of the absorption peak. Determining the diameter, length, and height of the embedded tube can optimize the sound absorption coefficient of the honeycomb cavity.

[0055] Then, the sound absorption coefficient of the overall honeycomb acoustic liner is optimized through parallel coupling design to achieve overall structural optimization design. It should be noted that this scheme does not obtain the overall structural design parameters by designing individual structures in parallel, but rather directly designs the relevant parameters of the overall structure through modeling.

[0056] The method will be explained in detail below.

[0057] I. Theoretical Model

[0058] The ratio of sound pressure (P) to volume velocity (V) is defined as the acoustic impedance Z. a Acoustic impedance is an important parameter used to describe the acoustic response characteristics of a material. The normal acoustic impedance determines the sound absorption coefficient of the sound-absorbing material.

[0059]

[0060] In the formula, Z0 is the characteristic impedance of the propagation medium, S is the incident area of ​​the sound wave, and the characteristic impedance of the sound wave propagating in the air is a constant Z0 = ρ0c0, where ρ0 is the air density and c0 is the static speed of sound in the air. From equation (1), it can be seen that when Z... a When the characteristic acoustic impedance Z0 / S is equal, the material can achieve perfect sound absorption.

[0061] like Figure 1-3 The honeycombresonators 1 with embedded apertures (MHREAs) with different depths are connected in parallel. Each honeycombresonator 1 is provided with an embedded aperture 2. The depth of each honeycombresonator 1 and the diameter and length of the corresponding embedded aperture 2 are different.

[0062] The side length of each cavity is w. s The diameter of the embedded tube is d i (i is the number of cavities), the length of the inner tube is l i The height of the entire cavity is L. i The wall thickness of the structures designed in this paper is t. a =1mm.

[0063] The embedded tube 2 has a cylindrical structure, and the honeycomb cavity 1 has a columnar structure with a hexagonal cross-section.

[0064] Each of the embedded tubes 2 is fixed at the center of one end of the corresponding honeycomb cavity 1, and the ends of each of the honeycomb cavities 1 with embedded tubes 2 are located on the same plane.

[0065] First, the propagation of sound waves within the cylindrical embedded tube and the hexagonal honeycomb cavity needs to be analyzed to obtain the equivalent wavenumber, equivalent air density, and equivalent sound velocity required for impedance calculation. Due to the small size of the structure, the wavenumber inside the structure should consider viscous losses and heat losses. The viscous wavenumber k in the cylindrical cavity... v and heat wave number k th They are respectively:

[0066]

[0067]

[0068] In the formula C P Let be the constant-pressure heat capacity, η be the dynamic viscosity of air, and K be the thermal conductivity. The viscous field and thermal field functions can be written as:

[0069]

[0070]

[0071] J n This is the nth-order solution of the Bessel function of the first kind. From this, the complex wavenumber, complex air density, and equivalent sound velocity in the cylindrical waveguide can be obtained:

[0072]

[0073]

[0074]

[0075] Where ω is the angular frequency. For a hexagonal cavity, the effect of thermal viscous loss is considered using the wide-tube approximation method. Its equivalent complex wavenumber, equivalent sound velocity, and equivalent air density can be expressed as:

[0076]

[0077]

[0078]

[0079] in γ is the heat capacity ratio, H d denoted as the hydraulic diameter of the cavity cross-section, and Pr as the Prandtl number.

[0080] To obtain the surface impedance of the entire parallel sound absorber, the acoustic impedance of each individual MHREA unit must first be calculated, and the internal air domain of each MHREA must be divided as follows: Figure 3 The diagram shows three sections, A, B, and C, representing the airspace below the embedded tube, around the embedded tube, and inside the embedded tube, respectively. The sound pressure and velocity between the inlet and outlet of each section satisfy the transfer matrix:

[0081]

[0082] The index n can be 1, 2, 3, or 4. P zn V zn and M zn They represent z respectively nThe sound pressure, volume velocity, and transfer matrix at the point. At the upper end of the embedded tube (z4), the transfer matrix, after considering the impedance correction at the tube end, can be written as:

[0083]

[0084] Where S C =π(d i / 2) 2 Let δ be the cross-sectional area of ​​the embedded tube, and δ1 be the impedance correction at the end of the embedded tube. The ratio is defined as follows: S A Let ξ be the cross-sectional area of ​​the hexagonal cavity in region A. When ξ < 0.4, the end correction value is... When ξ≥0.4, the terminal correction value is The fitting coefficients are a = 2 / 3, b = -26 / 15, and c = 16 / 15. Z0 = ρ0c0 is the characteristic impedance of air. For (z3) in the embedded tube, we have:

[0085]

[0086] k C Z is the equivalent wavenumber obtained from equation (6). C =ρ C c C The characteristic impedance of region C is obtained from equations (7) and (8). The incident sound wave through the embedded tube is split into two parts at z2 and enters regions A and B respectively. The boundary conditions are satisfied at the interface. At the same time P B / V B =-jcot[k B (l i -t a )]Z B / S B Considering the impedance correction δ2 at the end of the cylindrical embedded tube inside the cavity, the influence of frictional resistance in region B, and the boundary conditions, we can obtain:

[0087]

[0088] in,

[0089]

[0090] k B and Z B =ρ B c B The complex wavenumber and characteristic impedance of the medium in region B are obtained from equations (9)-(11), and the cross-sectional area of ​​region B is... In region A, there is a transfer matrix:

[0091]

[0092] k A and Z A =ρ A c A Given the complex wavenumber and characteristic impedance of the medium in region A obtained from equations (9)-(11), the transfer matrix of a single MHREA can be derived from the above derivation as follows:

[0093]

[0094] The bottom of the cavity has a hard boundary, therefore the impedance of each cavity can be determined by... To obtain.

[0095] II. Results Analysis and Discussion

[0096] In this study, the diameter d of the embedded tube i The length of the embedded tube is l i The height L of the entire cavity i All of these are optimizable structural variables. Based on the above theory, the influence of these three structural parameters on the sound absorption effect is first studied using the MHREA monomer. Figure 4 It showed w s The sound absorption curves of an MHREA monomer with diameter 15mm, d = 20.4mm, l = 3mm, and L = 24mm are shown. The curves demonstrate that the structure achieves perfect sound absorption at f = 258Hz, indicating that the thickness of the monomer structure is much smaller than the wavelength. Based on this, by individually adjusting d, l, and L, and according to the relationship between the geometric parameters and the sound absorption coefficient in the theoretical model, a contour plot of the sound absorption coefficient as a function of the structural parameters can be plotted. Figure 4 As shown in (b)-(c), it is evident from the figures that all three parameters significantly affect the position of the absorption peak of the MHREA monomer. Under constant conditions, reducing the diameter of the inner tube helps shift the absorption peak towards lower frequencies, while increasing the length of the inner tube also achieves low-frequency sound absorption. Changing the cavity depth can also adjust the position of the absorption peak. Achieving perfect sound absorption requires the rational design of these three structural parameters to achieve impedance matching.

[0097] The above research demonstrates that a single-unit structure with a tunable embedded tube and variable cavity depth can achieve perfect low-frequency sound absorption at a deep subwavelength dimension. Parallel connection of multiple perfect sound-absorbing units is a common method to broaden the sound absorption bandwidth, but this method often results in redundant structural thickness. Therefore, we adopt an overall design approach, considering the coupling effect between individual unit structures to reduce the acoustic liner thickness. Similarly, by paralleling multiple MHREA units, the overall surface impedance of the system after parallel connection can be expressed as:

[0098]

[0099] Near-perfect sound absorption can be achieved by adjusting the overall impedance. Based on the previous theoretical model, a design was developed as follows: Figure 5 The MHREAs shown have a maximum thickness of 35mm. The parallel coupling effect of multiple cavities makes the average sound absorption coefficient of the overall acoustic liner structure reach 0.92 in the 400-600Hz frequency band. The acoustic liner structure parameters are shown in Table 1.

[0100] Table 1 Figure 3 acoustic liner structure geometric parameters

[0101]

[0102] To verify the designed acoustic liner model, the finite element method was used to conduct a preliminary verification of the sound absorption effect of the structure. The boundary of the fine cavity structure was simulated using a thermoviscous sound field to fully consider the influence of viscosity and thermal effects on the sound absorption. Simultaneously, experimental samples were manufactured using 3D printing technology with photosensitive resin as the printing material and a printing accuracy of 0.1 mm. In the laboratory, a 50 mm square standing wave tube and two 1 / 4-inch sensors were used to measure the amplitude and phase information of the sound field to obtain the sound absorption coefficient and impedance of the experimental sample. Figure 5 (a) It can be seen that the acoustic liner achieves a good sound absorption effect in the target frequency band, and due to the coupling effect between the individual unit structures, the overall sound absorption effect is better than the sound absorption effect of a single MHREA at the corresponding frequency. Figure 5 (b) The acoustic impedance is around a position slightly greater than 1, while the acoustic impedance fluctuates around 0. This indicates that the system has basically achieved the impedance matching condition. The overall simulation and experimental results are in good agreement with the theoretical results. The deviation between the experiment and the theory and simulation may come from the errors in sample printing and assembly.

[0103] To further explain the mechanism of achieving good sound absorption, the concept of a complex frequency plane is introduced. Using f' = f e -jf i To replace the original real frequency, where f e This indicates the frequency component that includes the inherent losses of the structure, f. i This represents the additional complex frequency. Previous work by Zhou et al. has demonstrated that when the zero point (the point corresponding to the minimum value of ln|r'| in the figure) lies below the real axis of the complex frequency plane, i.e., when the system is in an overdamped state, the sound-absorbing structure can achieve optimal sound absorption with minimal thickness. From Figure 5 The zero-point position of this structure is almost always below the real axis (white dashed line), indicating that the acoustic liner has achieved near-optimal design. Furthermore, the real axis in the complex frequency plane represents the case where there is no imaginary frequency component, corresponding to the actual sound absorption performance of the acoustic liner structure.

[0104] MHREAs offer high design freedom, and the adjustability of their embedded tubes and cavity depth allows them to easily meet the design requirements of different target frequency bands. In this embodiment, the number of cavities is increased, with two additional wider-bandwidth acoustic liner structures designed using 14 and 23 MHREA units in parallel, respectively, to verify the feasibility of this acoustic liner configuration in low-frequency broadband sound absorption applications. Figure 6 As shown, these two acoustic liners, with maximum thicknesses of 45mm and 51mm respectively, achieved excellent sound absorption in the 400-800Hz and 600-1600Hz ranges (both theoretical and experimental average sound absorption coefficients reached 0.92). Tables 2 and 3 provide the structural parameters of the two acoustic liners. The impedance curves of these two acoustic liners are consistent with the overdamped design target, achieving impedance matching across the entire frequency band, and the theoretical and experimental results agree well.

[0105] Table 2 Figure 6 (a) Geometric parameters of the acoustic liner structure

[0106]

[0107]

[0108] Table 3 Figure 6 (c) Geometric parameters of the acoustic liner structure

[0109]

[0110] III. Conclusion

[0111] This study adds an embedded tube structure to the traditional honeycomb acoustic liner configuration and incorporates the cavity depth of the honeycomb cavity as a designable parameter. Considering viscous and thermal losses, a theoretical model of the acoustic liner structure is constructed using the transfer matrix method. Based on this theoretical model, the effects of three designable structural parameters—the diameter, length, and cavity depth of the embedded tube—on the sound absorption performance of the individual acoustic liner structures are investigated. Finally, considering the coupling effect between the individual liners, three acoustic liner structures with maximum thicknesses of 35mm, 45mm, and 51mm are designed, achieving broadband low-frequency sound absorption effects in the 400-600Hz, 400-800Hz, and 600-1600Hz ranges, respectively, with average sound absorption coefficients exceeding 0.92. Compared to traditional acoustic liner structures, this design is thinner and lighter. The collaborative design of multiple degrees of freedom and the consideration of coupling effects between individual structures significantly reduce the acoustic liner thickness. The overall configuration is simple and easy to manufacture, making it promising for applications in engineering fields such as noise reduction in aero-engines.

[0112] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations, characterized in that, The honeycomb acoustic liner includes multiple honeycomb cavities connected in parallel, each honeycomb cavity having an embedded tube. The method includes constructing an acoustic liner with optimal sound absorption in a specific frequency band by optimizing the diameter and length of the embedded tube in each honeycomb cavity and the height of the entire honeycomb cavity. The method specifically includes constructing a transfer matrix model for each honeycomb cavity, thereby calculating the overall surface impedance of the honeycomb acoustic liner, and optimizing the inner tube diameter, inner tube length and height of each honeycomb cavity to achieve the optimal average sound absorption coefficient of the honeycomb acoustic liner within a specific frequency band. The expression for the transfer matrix model of each cellular cavity is as follows: In the formula, For a single cellular cavity, the transfer matrix model is... To account for the transfer matrix after correction of the pipe end impedance, Let C be the transfer matrix of the air domain C in the embedded tube. Let B be the transfer matrix of the air domain B surrounding the embedded tube. Let A be the transfer matrix of the air domain A below the embedded tube. The imaginary unit, The sound wavenumber in air. To correct the impedance at the end of the embedded tube, The characteristic impedance of air dielectric is... This represents the cross-sectional area of ​​the embedded tube. The equivalent complex wavenumber in a cylindrical waveguide. The length of the embedded tube. Let be the characteristic impedance of region C. Impedance correction for the end of the cylindrical embedded tube inside the cavity. The dynamic viscosity of air. Angular frequency, Let be the equivalent complex wavenumber of the medium in region B. The thickness of the honeycomb cavity wall. Let B be the cross-sectional area of ​​region B. Let be the characteristic impedance of the medium in region B. Let A be the equivalent complex wavenumber of the medium in region A. Let A be the length of region A. Let A be the characteristic impedance of the dielectric in region A. Let A be the cross-sectional area of ​​region A. This refers to air density.

2. The method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations according to claim 1, characterized in that, By using parallel coupling design, the diameter, length and height of each embedded tube in the overall honeycomb acoustic liner are designed to optimize the sound absorption coefficient of the overall honeycomb acoustic liner.

3. The method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations according to claim 1, characterized in that, The expression for calculating the equivalent complex wavenumber of a hexagonal cavity is as follows: In the formula, Let be the equivalent complex wavenumber of the hexagonal cavity. The static speed of sound in air. The hydraulic diameter of the cavity cross-section. For heat capacity ratio, For Prandtl numbers, For constant pressure heat capacity, is the thermal conductivity.

4. The method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations according to claim 1, characterized in that, The expression for calculating the impedance of a single cell cavity is: In the formula, For the first i The impedance of each honeycomb cavity; The expression for calculating the surface impedance of the honeycomb acoustic liner is as follows: In the formula, The overall surface impedance of the honeycomb acoustic liner.

5. The method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations according to claim 4, characterized in that, The formula for calculating the sound absorption coefficient is as follows: In the formula, The sound absorption coefficient is... The characteristic impedance of the propagation medium, Let be the incident area of ​​the sound wave.

6. The method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations according to claim 1, characterized in that, The honeycomb cavity (1) is a columnar structure with a hexagonal cross-section.

7. The method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations according to claim 1, characterized in that, The embedded tube (2) has a cylindrical structure.

8. The method for constructing a honeycomb acoustic liner based on an embedded tube and different cavity depth configurations according to claim 1, characterized in that, Each of the embedded tubes (2) is fixed at the center of one end of the corresponding honeycomb cavity (1).

Images