Low-flow-resistance wire mesh composite panel aviation linear acoustic liner

Abstract

The invention discloses a low-flow-resistance metal wire mesh composite panel aviation linear acoustic liner, which comprises a composite panel, a honeycomb and a bottom plate, and is characterized in that the composite panel is formed by compounding a fine screen mesh, a thick screen mesh and a perforated film; wherein the fine screen mesh provides viscous acoustic resistance and dissipates acoustic energy; the thick silk screen ensures the structural strength of the composite panel and plays a supporting role; the perforated film on the outer surface of the acoustic liner can reduce surface roughness and flow resistance; according to the composite panel, incident sound energy is dissipated into heat energy, the viscous acoustic resistance of the composite panel can be improved, the swept flow acoustic impedance and the sensitivity of the swept flow acoustic impedance along with the change of the swept flow are reduced, the swept flow effect is better inhibited, and the excellent aviation high-speed swept flow linear characteristic is formed. Therefore, according to the low-flow-resistance wire mesh composite panel aviation linear acoustic liner, better noise reduction in a wider flow speed range can be achieved, and meanwhile the flow resistance and the oil consumption rate are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of sound linings, and in particular relates to an aviation linear sound lining with a low flow resistance metal wire mesh composite panel. Background Art

[0002] The noise of large civil aircraft is mainly divided into two parts: body noise and engine noise. The engine is undoubtedly the most important noise source and the focus of aviation noise reduction. The use of anechoic nacelles and duct acoustic lining technology is currently the most important means of engine noise reduction. At present, the aeroacoustic environment in the nacelle of modern aircraft engines is mainly characterized by high sound intensity and high flow velocity. The operating conditions in the flight envelope change particularly significantly, making noise reduction extremely difficult. The acoustic performance of traditional acoustic liners will show great differences under different operating conditions due to the high sound intensity effect and grazing effect of the perforated panel. The high sound intensity effect refers to the fact that when the sound pressure level increases to a certain value, the incident sound wave excites a micropore jet in the micropore, which affects the movement of the sound particles in the hole, thereby causing the micropore acoustic impedance to change with the sound pressure level. The grazing effect refers to the formation of an unstable vortex layer when the airflow flows through the leading edge of the small hole, which produces vortex shedding after acoustic disturbance, converting the sound energy into vortex kinetic energy. This means that the acoustic resistance of the perforated plate will increase with the increase of airflow velocity, while the acoustic reactance will decrease with the increase of Mach number. This part of the acoustic impedance is called the grazing flow acoustic impedance. However, aircraft engines have an optimal acoustic impedance for achieving maximum noise reduction under each operating condition, which means that the larger the acoustic resistance, the better, and the smaller the acoustic reactance, the better. This makes it difficult for traditional acoustic liners to achieve the optimal acoustic impedance under all operating conditions within the aircraft flight envelope. In addition, the surface of the acoustic liner will bring additional aerodynamic resistance compared to the rigid wall (smooth wall without noise reduction effect), which has a direct impact on the fuel consumption of the aircraft. In order to reduce fuel consumption and improve fuel efficiency, the design of the acoustic liner must also reduce the resistance caused by the acoustic resistance as much as possible.

[0003] Considering the noise reduction problem of the aeroengine duct, the optimal acoustic resistance and acoustic reactance decrease and increase respectively with the increase of Mach number, and both gradually tend to be stable at high Mach numbers. This requires that when designing the acoustic liner, the threshold of the high sound intensity effect should be increased as much as possible, while reducing the sensitivity of its acoustic impedance to the grazing flow. Traditional perforated plate acoustic liners mainly use the grazing flow effect to reduce noise. Their acoustic impedance is extremely sensitive to high sound pressure levels and grazing flow, and the perforated panel will bring greater aerodynamic resistance. Therefore, it is necessary to further develop aviation low-resistance linear acoustic liners that are less sensitive to high sound intensity and grazing flow changes and more in line with the most likely acoustic impedance change trend, so as to achieve optimal noise reduction in a wider flow rate range. Summary of the invention

[0004] The object of the present invention is to provide a low flow resistance metal wire mesh composite panel aviation linear sound liner to solve the technical problem in the prior art that the existing sound liner cannot achieve the optimal noise reduction effect.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention also provides a low flow resistance metal wire mesh composite panel aviation linear sound lining, comprising:

[0007] A perforated film, a fine wire mesh and a coarse wire mesh, wherein the fine wire mesh and the coarse wire mesh constitute a composite panel with sound dissipation function; wherein,

[0008] The perforated film is used to reduce the roughness of the metal wire mesh on the surface of the sound liner, thereby reducing air resistance.

[0009] The fine mesh is used to provide viscous acoustic resistance, has a sound absorption effect of dissipating sound energy, and reduces the sensitivity of the sound lining performance to high-speed flow and high sound intensity;

[0010] The coarse wire mesh is used to ensure the structural strength of the composite panel and plays a supporting role;

[0011] The coarse wire mesh plays a certain auxiliary sound absorption role;

[0012] Preferably, the composite panel can reduce the jet velocity, characteristic length and vortex Mach number in the micropores of the sintered wire mesh, so that its acoustic resistance does not substantially change with the sound pressure level under the condition of no grazing flow, thereby suppressing the high sound intensity effect;

[0013] Preferably, the composite panel can reduce the resistance experienced by the sound liner;

[0014] Preferably, the composite panel is used to suppress the sweeping flow effect and reduce the sensitivity of its acoustic performance to the sweeping flow, thereby meeting the optimal acoustic impedance of the aero-engine nacelle and maintaining the sound absorption performance within a wide range of Mach numbers;

[0015] As well as suppressing the high sound intensity effect and raising the threshold for the occurrence of high sound pressure level effect.

[0016] Preferably, the perforated film, the wire mesh, the honeycomb and the bottom plate are bonded by adhesive or welding, or,

[0017] The perforated film, fine wire mesh, honeycomb and bottom plate are bonded by adhesive or welding, or,

[0018] The perforated film, fine wire mesh, coarse wire mesh, honeycomb and bottom plate are bonded by adhesive or welding;

[0019] The cross-section of the honeycomb is in the shape of a regular hexagon, a square or a circle.

[0020] Preferably, the fine wire mesh or coarse wire mesh in the composite panel is a microporous panel with drag reduction and dissipation effect, and the thickness of the perforated film in the composite panel is less than 0.2 mm.

[0021] Preferably, the structures of the low flow resistance metal wire mesh composite panel aviation linear acoustic liner are arranged in the order of the perforated film, the fine wire mesh, the coarse wire mesh, the honeycomb and the bottom plate.

[0022] Preferably, the structures of the low flow resistance metal wire mesh composite panel aviation linear acoustic liner are arranged in the order of the perforated film, the coarse wire mesh, the fine wire mesh, the honeycomb and the bottom plate.

[0023] Preferably, the structures of the low flow resistance metal wire mesh composite panel aviation linear acoustic liner are arranged in the order of the perforated film, the fine wire mesh, the coarse wire mesh, the fine wire mesh, the honeycomb and the bottom plate.

[0024] Preferably, the perforation rate of the perforated film is adjusted to achieve noise reduction conditions in specific noise reduction scenarios.

[0025] Preferably, the number of fine meshes and / or coarse meshes is adjusted to achieve noise reduction conditions in a specific noise reduction scenario.

[0026] Preferably, the low flow resistance metal wire mesh composite panel aviation linear acoustic liner is arranged on the aerodynamic surface of an aircraft engine, an auxiliary power unit, a fuselage, a wing or a horizontal vertical tail.

[0027] Beneficial effects:

[0028] The low flow resistance metal wire mesh composite panel aviation linear acoustic lining of the present application is applied to aircraft engines, which can reduce the resistance of the acoustic lining, reduce fuel consumption, and increase the threshold of the high sound intensity effect. At the same time, it reduces the sensitivity of its acoustic impedance to the incoming flow velocity, and can maintain a good noise reduction effect within the flight envelope of the aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings constituting a part of this application are used to provide a further understanding of this application, so that other features, purposes and advantages of this application become more obvious. The schematic embodiment drawings and their descriptions of this application are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0030] Figure 1 A schematic diagram of the structure of a low flow resistance metal wire mesh composite panel aviation linear acoustic liner provided in an embodiment of the present application;

[0031] Figure 2 A schematic diagram of the structure of another low-flow resistance metal wire mesh composite panel aviation linear acoustic liner provided in an embodiment of the present application;

[0032] Figure 3 A schematic diagram of the structure of another low-flow resistance metal wire mesh composite panel aviation linear acoustic liner provided in an embodiment of the present application;

[0033] Figure 4 A schematic diagram of the configuration of a traditional perforated plate acoustic liner and a low flow resistance metal wire mesh composite panel aviation linear acoustic liner provided in an embodiment of the present application;

[0034] Figure 5 A schematic diagram of the structure of a flow tube test bench provided in an embodiment of the present application;

[0035] Figure 6 A curve diagram of the acoustic impedance of an acoustic liner changing with the incident sound pressure level at 1200 Hz without swept flow provided in an embodiment of the present application;

[0036] Figure 7 A schematic diagram of the structure of a two-dimensional flow tube with equal cross-section provided in an embodiment of the present application;

[0037] Figure 8 An optimal acoustic impedance curve diagram for simplifying the noise reduction problem of an aircraft engine external duct after the transmission at 1000Hz provided in an embodiment of the present application;

[0038] Fig. 9 The variation curves of the grazing flow acoustic resistance with the grazing flow velocity at 130 dB incident sound pressure level and different frequencies for a traditional perforated plate acoustic liner and a low flow resistance metal wire mesh composite panel aviation linear acoustic liner provided in the embodiments of the present application;

[0039] Fig.10 A curve diagram showing the variation of grazing flow acoustic impedance with grazing flow velocity at 130 dB and different frequencies for a traditional perforated plate acoustic liner and a low flow resistance metal wire mesh composite panel aviation linear acoustic liner provided in an embodiment of the present application;

[0040] Fig.11 A schematic diagram of an engine structure provided in an embodiment of the present application;

[0041] Fig.12 A schematic diagram of a longitudinal cross-section of an engine intake duct provided in an embodiment of the present application.

[0042] Description of Figure Numbers

[0043] 1. Fine metal wire mesh, 2. Coarse metal wire mesh, 3. Honeycomb, 4. Bottom plate, 5. Inlet silencer section, 6. Sound source, 7. Pitot tube, 8. Sound liner mounting box, 9. Outlet silencer section, 10. Perforated film, 11. Connecting rod, 12. Aerodynamic surface. DETAILED DESCRIPTION

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in combination with the drawings and the description of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0045] Example:

[0046] The present application also proposes a low flow resistance metal wire mesh composite panel aviation linear sound lining, comprising:

[0047] A perforated film, a fine wire mesh and a coarse wire mesh, wherein the perforated film, the fine wire mesh and the coarse wire mesh constitute a composite panel with dissipative effect, wherein:

[0048] The coarse wire mesh is used to ensure the structural strength of the composite panel and plays a supporting role;

[0049] The fine wire mesh is used to provide viscous acoustic resistance and has a supporting effect.

[0050] The perforated film has a thickness of less than 0.2 mm, which can reduce the surface roughness and flow resistance on the outer surface of the sound liner;

[0051] The composite panel is bonded to one side of the honeycomb with hexagonal, rectangular and / or various cross-sectional cavities, while the other side of the honeycomb is bonded to the bottom plate. The composite panel can reduce the jet velocity, characteristic length and vortex Mach number in the sintered wire mesh micropores, so that its acoustic resistance basically does not change with the sound pressure level under non-grazing flow conditions, thereby suppressing the high sound intensity effect.

[0052] The composite panel can improve the viscous acoustic resistance of the composite panel, while inhibiting the generation of shedding vortices and reducing the sensitivity of its acoustic performance to grazing flow, so that it can meet the optimal acoustic impedance and achieve good sound absorption performance within a wide range of Mach numbers.

[0053] Specifically, the low flow resistance metal wire mesh composite panel aviation linear sound lining of the present application includes a perforated film, a fine metal wire mesh and a coarse metal wire mesh. The coarse wire mesh is used to ensure the structural strength of the composite panel, plays a supporting role, and can also play a certain auxiliary sound absorption role; the fine wire mesh can provide a large amount of viscous acoustic resistance and has a certain supporting role. The pure wire mesh panel can reduce the jet velocity, characteristic length and vortex Mach number in the micropores of the sintered wire mesh, so that its acoustic resistance basically does not change with the sound pressure level under the condition of no grazing flow, thereby suppressing the high sound intensity effect. The composite panel can convert the sound energy entering the composite panel into heat energy to increase the viscous acoustic resistance of the composite panel, reduce the grazing flow acoustic impedance and the sensitivity of its acoustic impedance to changes in grazing flow, thereby better suppressing the grazing flow effect. The low-resistance metal wire mesh composite panel aviation linear acoustic lining is set on the aerodynamic surface of the aircraft engine. The acoustic impedance of the low-resistance metal wire mesh composite panel aviation linear acoustic lining of the present application does not change much with the increase of Mach number, which is closer to the optimal acoustic impedance change trend of the aeroengine culvert after-transmission noise reduction. It should be noted that the perforated film has less resistance than only fine wire mesh and / or coarse wire mesh, which can effectively reduce the fuel consumption of the aircraft.

[0054] In some embodiments, the low flow resistance metal wire mesh composite panel aviation linear sound liner further comprises:

[0055] A honeycomb and a bottom plate, wherein the honeycomb and the bottom plate are adhesively bonded;

[0056] The honeycomb has a structure of a regular hexagon, a square or a circle.

[0057] Specifically, the acoustic linings in the prior art are traditional perforated plate acoustic linings and metal wire mesh perforated plate acoustic linings. When there is no grazing flow, the sound waves excite eddies near the small holes, causing the sound pressure level to increase to a certain value, and the acoustic resistance increases accordingly. This phenomenon is called the high sound pressure level effect. When there is grazing flow, the change in the acoustic performance of the traditional acoustic lining is mainly caused by the grazing flow effect of the perforated panel. The grazing flow effect provides the most important acoustic energy dissipation mechanism for the traditional perforated plate acoustic lining: the grazing flow flowing through the leading edge of the small hole will form an unstable vortex layer, which will produce vortex shedding after acoustic disturbance, converting the acoustic energy into vortex kinetic energy; the acoustic resistance of the perforated plate will increase linearly, and this part of the acoustic resistance is called the grazing flow acoustic resistance; its acoustic energy dissipation is proportional to the square of the grazing flow velocity, which is similar to the high sound pressure level effect, so it can also be classified as a nonlinear effect. Because of this nonlinear effect, it is difficult for an aircraft to achieve the optimal acoustic impedance under all working conditions within the flight envelope.

[0058] The acoustic impedance of traditional perforated plate acoustic lining is sensitive to the sound pressure level and changes with the glancing flow. To solve this problem, linear acoustic lining came into being. Its viscous acoustic resistance accounts for a larger proportion than the former, so the glancing flow acoustic resistance is smaller. The metal mesh perforated plate acoustic lining is the most typical microporous linear acoustic lining, which is composed of a fine metal wire mesh attached to the surface of the perforated plate acoustic lining, and the mesh pore size is as small as tens of microns. This increases its viscous acoustic resistance and thus has a good linear characteristic to the sound pressure level. However, when the Mach number is too high, the glancing flow effect of the metal mesh perforated plate acoustic lining cannot be ignored. The acoustic lining of the present application also includes a honeycomb and a base plate, and the honeycomb and the base plate are adhesively bonded. The cross-sectional structure of the honeycomb of the present application is a regular hexagon and / or square and / or other geometric structure.

[0059] In some embodiments, the variation trend of the acoustic impedance of the low-resistance metal wire mesh composite panel aviation linear acoustic lining with Mach number can be adjusted by optimizing the perforation rate of the perforated film, the mesh number of the fine and coarse wire mesh, and the number of wire meshes, so that it is more consistent with the variation trend of the optimal acoustic impedance with Mach number required by a specific noise reduction scenario. The optimal acoustic impedance and optimal acoustic reactance of the aft nacelle of an aircraft engine culvert decrease and increase respectively with the increase of Mach number, and gradually tend to be stable; the acoustic impedance and acoustic reactance of a traditional acoustic lining increase and decrease respectively with the increase of Mach number; and the acoustic impedance of the low-resistance metal wire mesh composite panel aviation linear acoustic lining of the present application basically does not change with the increase of Mach number, so it can provide efficient sound absorption performance in a wider range of Mach numbers.

[0060] In the embodiments of the present application, Figure 1 The present invention is a schematic diagram of the structure of a low flow resistance metal wire mesh composite panel aviation linear acoustic lining, wherein the structure is arranged in the order of the fine metal wire mesh, the coarse metal wire mesh, the honeycomb and the bottom plate.

[0061] In another embodiment of the present application, Figure 2 A schematic diagram of the structure of another low-resistance metal wire mesh composite panel aviation linear acoustic liner provided in an embodiment of the present application, wherein the structure is arranged in the order of the coarse metal wire mesh, the fine metal wire mesh, the honeycomb and the bottom plate,

[0062] In another embodiment of the present application, Figure 3 A schematic structural diagram of another low flow resistance metal wire mesh composite panel aviation linear acoustic lining provided in an embodiment of the present application, wherein the structures are arranged in the order of the fine metal wire mesh, the coarse metal wire mesh, the fine metal wire mesh, the honeycomb and the bottom plate.

[0063] It should be noted that the three acoustic lining structures of the present application all have good viscous acoustic resistance and can maintain excellent noise reduction performance in an environment where the Mach number changes drastically.

[0064] In order to verify the performance of the acoustic liner of this application, an experimental comparison was conducted between the traditional perforated plate acoustic liner and the low flow resistance metal wire mesh composite panel aviation linear acoustic liner. Figure 4 The schematic diagrams of the configurations of the two acoustic liners are given, and the parameters of each acoustic liner are shown in Table 1.

[0065] Table 1 Structural parameters of the experimental pieces

[0066]

[0067] right Figure 4 The traditional perforated plate acoustic lining and low flow resistance metal wire mesh composite panel aviation linear acoustic lining are tested and studied. Both acoustic liners are single-degree-of-freedom acoustic liners with an effective length of 550 mm, an effective width of 51 mm, a cavity depth Lc of 51 mm, and a resonant frequency of 1200 Hz. The traditional perforated plate acoustic lining panel is an aluminum perforated plate with a hole diameter d and a thickness t of 1 mm and a perforation rate of 8.856%. The low flow resistance metal wire mesh composite panel aviation linear acoustic lining composite panel is made of a perforated film and a layer of sintered metal wire mesh. The upper layer is a finer dense wire mesh MXW200 / 51, and the lower layer is a coarser plain wire mesh GFW0.4 / 0.125.

[0068] This application detects the grazing flow characteristics of low-resistance metal wire mesh composite panel aviation linear sound lining, which is mainly obtained by conducting experiments on traditional perforated plate sound lining and low-resistance metal wire mesh composite panel aviation linear sound lining on a flow tube test bench. The main steps of the experimental operation on the flow tube test bench are: Step 1: Install the sound lining, which includes a perforated plate sound lining and a low-resistance metal wire mesh composite panel aviation linear sound lining, and the sound lining is installed in the acoustic measurement section in the flow tube test bench. Step 2: Conduct a high sound pressure level experiment, determine the acoustic impedance of each sound lining corresponding to the incident sound pressure level according to different incident sound pressure levels, and find the optimal incident sound pressure level of the grazing flow experiment. Step 3: Conduct a grazing flow experiment, determine the acoustic impedance, grazing flow acoustic resistance and grazing flow acoustic reactance of each sound lining at different frequencies and different Mach numbers based on the optimal incident sound pressure level, and then analyze and detect the grazing flow characteristics of the low-resistance metal wire mesh composite panel aviation linear sound lining.

[0069] Step 1: Install the acoustic liner, which includes a perforated plate acoustic liner and a low-resistance metal wire mesh composite panel aviation linear acoustic liner, and the acoustic liner is installed in the acoustic measurement section of the flow tube test bench.

[0070] Specifically, the perforated plate acoustic liner and the low flow resistance metal wire mesh composite panel aviation linear acoustic liner are installed in the acoustic measurement section of the flow tube test bench. The acoustic liner installation box fixes the acoustic liner and makes its upper surface flush with the lower wall of the pipe to form an internal flow channel together. In one embodiment, the perforated plate acoustic liner and the low flow resistance metal wire mesh composite panel aviation linear acoustic liner can be installed in the acoustic measurement sections of two flow tube test benches respectively to facilitate subsequent detection and analysis. In another embodiment, in the step of installing the acoustic liner, after an experimental condition is completed, the current acoustic liner can be removed and another acoustic liner can be installed. The end of one experimental condition is specifically to determine the acoustic impedance of each acoustic liner at different frequencies and different flow rates. The flow tube test bench of the present application is used for acoustic experiments on flow channels in a wide frequency range. The inner cross-section of the flow tube is 63×51mm 2 The device is a rectangle, including the air source, sound source section, flow field measurement section, acoustic measurement section and inlet and outlet silencer sections.

[0071] In order to accurately detect the sweeping flow characteristics of the low flow resistance metal wire mesh composite panel aviation linear acoustic liner, in some embodiments, the flow tube test bench includes:

[0072] The air source section includes a centrifugal fan, a honeycomb, a damping net, a flow stabilizer, and a muffler, and is used to supply a 0-0.6 Mach airflow to the flow tube;

[0073] Flow field measurement section, used to obtain flow field information such as average velocity in the pipeline;

[0074] The acoustic measurement section is provided with a microphone for measuring the sound pressure information of the attenuation along the sound lining section and monitoring the incident and reflected sound signals of the sound lining;

[0075] The inlet and outlet silencer sections are used to provide reflection-free conditions at both ends of the flow tube.

[0076] Specifically, Figure 5The schematic diagram of the structure of the flow tube test bench device includes: ① The air source section is the upstream acoustic wind tunnel, which includes a centrifugal fan, honeycomb, damping net, flow stabilizer, and muffler, and can supply 0 to 0.6 Mach airflow to the flow tube. ② The sound source section consists of 4 BMS 4592 speakers, which are located upstream of the acoustic measurement section in this experiment. Its driving signal is provided by computer software through NI USB6259AO and power amplifier. ③ The pitot tube in the flow field measurement section is driven by a two-dimensional high-precision stepper motor combination, which can obtain detailed information on the flow field such as the average velocity in the pipeline. ④ The acoustic measurement section uses an acoustic liner mounting box to fix the acoustic liner and make its upper surface flush with the lower wall of the pipeline to form an internal flow channel. There are 20 GRAS46BD microphones in this section: 16 of them are installed directly above the sound lining to be measured, used to measure the sound pressure information of the sound lining section attenuation along the way; a pair of microphones with a spacing of 25mm are installed upstream of the sound lining to monitor the incident / reflected sound signals upstream of the sound lining; there is also a pair of microphones downstream of the sound lining to monitor the local sound signal. ⑤ The inlet and outlet anechoic sections all adopt a variable cavity depth structure to enhance the broadband noise reduction effect and provide non-reflection conditions for both ends of the flow tube. In addition, the pipe wall temperature is measured by an embedded TP3001 thermometer, and the atmospheric pressure is measured by an HHP350 barometer.

[0077] Step 2: Conduct a high sound pressure level experiment, determine the acoustic impedance of each sound liner corresponding to the incident sound pressure level according to different incident sound pressure levels, and find out the optimal incident sound pressure level of the grazing flow experiment.

[0078] The incident sound pressure levels include 110dB, 120dB, 130dB, 135dB, 140dB, and 145dB. The test frequency is 1200Hz, the resonance frequency of the sound liner, and the grazing flow velocity is 0m / s. By obtaining the data, we analyze and explore the starting sound pressure level of the high sound intensity effect of each sound liner, and finally determine the optimal incident sound pressure level for the grazing flow effect study.

[0079] like Figure 6The graph shows the change of acoustic impedance of the acoustic liner with the incident sound pressure level at 1200Hz without grazing flow. When the incident sound pressure level is 130dB or below, the acoustic impedance curves of the two acoustic liners do not change significantly with the sound pressure level. Until 135dB or above, the acoustic impedance of the traditional perforated plate acoustic liner begins to increase with the sound pressure level, that is, the high sound intensity effect appears, while the acoustic impedance of the low flow resistance metal wire mesh composite panel aviation linear acoustic liner is almost unchanged until 145dB, which means that the low flow resistance metal wire mesh composite panel aviation linear acoustic liner can well suppress the high sound intensity effect. Based on this, in order to avoid the interference of the high sound intensity effect on the grazing flow and take into account the high signal-to-noise ratio, when testing the grazing flow characteristics of the low flow resistance metal wire mesh composite panel aviation linear acoustic liner, the incident sound pressure level is selected as the highest value before the high sound intensity effect appears when there is no grazing flow, that is, 130dB. The grazing flow acoustic resistance is the total acoustic resistance minus the acoustic resistance at zero flow velocity, and the grazing flow acoustic reactance is the total acoustic reactance minus the acoustic reactance at zero flow velocity.

[0080] Step three, conducting a grazing flow experiment, determining the acoustic impedance, grazing flow acoustic resistance and grazing flow acoustic reactance of each acoustic liner at different frequencies and different Mach numbers based on the optimal incident sound pressure level, and then analyzing and detecting the grazing flow characteristics of the metal wire mesh acoustic liner.

[0081] This application relates to the extraction and calculation of acoustic impedance. Figure 7 The paper shows a two-dimensional flow tube with a height of b and a local reactive acoustic liner with a length of L installed flush with the lower wall of the pipe. There is a uniform flow with a velocity of 0 in the pipe, and the plane incident wave propagates from the upstream rigid wall section to the downstream acoustic liner section. In order to accurately extract the unknown acoustic impedance Z of the acoustic liner, J equidistant microphones are installed on the opposite wall of the acoustic liner to measure the sound pressure information along the liner, and the sound pressure information upstream and downstream of the acoustic liner is respectively obtained by and In addition, a coordinate system (x, y) is introduced, where x and y represent the axial and vertical coordinates respectively, and the position where j = 1 is the origin of the coordinate system.

[0082] The acoustic field of the flow tube acoustic liner can be expressed in the form of mode superposition as follows:

[0083]

[0084] in, represents the complex mode amplitude, and the superscripts ‘±’ represent the forward and backward modes, respectively. and and represent the axial and vertical wave numbers associated with the vertical mode order n, respectively. These wave numbers are related by the dispersion relation.

[0085]

[0086] Here, the free space wave number k = w / c0, where w is the angular frequency, c0 is the speed of sound, and the Mach number Ma = V 0 / c0.

[0087] Furthermore, according to the acoustic field solution (1) and the Ingard-Myers acoustic impedance boundary condition, the characteristic equation of the unknown acoustic impedance Z of the acoustic liner can be derived:

[0088]

[0089] Therefore, the key to extracting the unknown acoustic impedance of the acoustic liner lies in the determination of the wave number in equation (3), and the Prony method is introduced to solve it. The J microphone measurement points are all located on the upper wall, and equation (1) is truncated to the Nth order vertical mode, then the sound pressure at point j can be further expressed as: The sound field of the flow tube acoustic liner section can be written in the form of mode superposition, as follows:

[0090]

[0091] Here, Δx is the distance between adjacent measuring points, and J ≥ 2N is required. Note that the corresponding forward and backward transmission information is implicit in the value of the complex axial wave number.

[0092] Furthermore, equation (4) can be written as a system of equations containing JN equations:

[0093]

[0094] Here, assuming it is the solution of the N-order polynomial (6),

[0095]

[0096] Multiply both ends of equation (5) by C s , and combined with equation (6), we can get:

[0097]

[0098] It can be seen that once the coefficient C in formula (7) is determined s , we can get the root of the N-order polynomial through equation (6), and then get the axial wave number k xn , and then combined with the dispersion relationship between the wave numbers (2), the vertical wave number k can be obtained yn , and finally substitute it into the characteristic equation (3) to obtain the acoustic impedance Z.

[0099] Figure 8A noise reduction problem of modal waves (circumferential modal order is 5) in a straight annular tube with a radius of 1m and a hub ratio of 0.7, which is simplified from the sound transmission problem behind the aeroengine shroud, is considered. The sound propagation direction is consistent with the direction of the grazing flow. At 1000Hz, the optimal acoustic resistance and acoustic reactance decrease and increase respectively with the increase of Mach number, and both gradually tend to be stable at high Mach numbers.

[0100] Fig. 9 The following are the curves of the variation of the grazing flow acoustic resistance with the grazing flow velocity at 130dB and different frequencies for the traditional perforated plate acoustic lining and the low-resistance metal wire mesh composite panel aviation linear acoustic lining. The grazing flow acoustic resistance Rg and the grazing flow acoustic reactance Xg are obtained by subtracting the acoustic impedance without grazing flow from the total acoustic impedance. As shown in the figure, the trend of the traditional perforated plate acoustic lining with the increase of Mach number can be roughly divided into: non-increasing section and linear increasing section. In the non-increasing section, it does not change or increases slightly with the Mach number, so there is a gentle area. In the increasing section, it almost increases linearly with the Mach number. For example, at 1000Hz, it starts to increase when the Mach number is about 0.05, and the grazing flow acoustic resistance Rg increases to about 1.2 when the Mach number increases to 0.6. As for the new low-resistance metal wire mesh composite panel aviation linear acoustic lining, since its panel is entirely composed of microporous linear materials, its grazing flow acoustic resistance curve does not show a very obvious increase like the traditional perforated plate acoustic lining, and the fluctuation amplitude at all measurement frequencies is very small, basically maintained within ±0.6. Especially at 1000Hz, the grazing flow acoustic resistance Rg of the new low-resistance metal wire mesh composite panel aviation linear acoustic liner remains near 0 in the range of Mach number from 0 to 0.6. This shows that the proposed low-resistance metal wire mesh composite panel aviation linear acoustic liner has the best acoustic linear characteristics and has a grazing flow effect suppression effect that is far superior to that of the traditional perforated plate acoustic liner.

[0101] Fig.10 The following is a curve showing the variation of the glancing flow acoustic impedance of the traditional perforated plate acoustic lining and the low-resistance metal wire mesh composite panel aviation linear acoustic lining with the Mach number. The acoustic impedance Xg of the traditional perforated plate acoustic lining and the new low-resistance metal wire mesh composite panel aviation linear acoustic lining will change with the increase of the Mach number, but the variation range of the glancing flow acoustic impedance of the new low-resistance metal wire mesh composite panel aviation linear acoustic lining with the Mach number is significantly weaker than that of the perforated plate acoustic lining. For example, at 2000Hz, in the process of the Mach number increasing from 0 to 0.6, the glancing flow acoustic impedance Xg of the traditional perforated plate acoustic lining decreases from 0 to about -1, while the glancing flow acoustic impedance of the new low-resistance metal wire mesh composite panel aviation linear acoustic lining changes by no more than ±0.2. This shows that the low-resistance metal wire mesh composite panel aviation linear acoustic lining of the present application has a better suppression effect on the entire glancing flow effect including the glancing flow acoustic impedance Rg and the glancing flow acoustic impedance Xg, is closer to the optimal acoustic impedance variation trend of the aero-engine duct noise reduction, and has a better noise reduction effect.

[0102] Fig.11The aircraft engine model on display has its body connected to the wing through a connecting rod 11. The airflow entering the engine is called aerodynamic airflow, which can be divided into two parts. The first part enters the power unit to participate in combustion, and the second part enters the annular pipe formed by the inner wall of the engine and the outer wall of the power unit. The contact surface between the aerodynamic airflow and the engine skin is called the aerodynamic surface. In order to reduce noise pollution, sound lining has been used on the aerodynamic surface to absorb part of the sound energy. For example, the longitudinal section of the engine Fig.12 As shown, the acoustic liner is mounted on the aerodynamic surface 22 .

[0103] 1) The low-resistance metal wire mesh composite panel aviation linear acoustic liner proposed in this application removes the traditional perforated plate structure and uses low-resistance metal wire as the composite panel. The composite panel not only dissipates the incident sound energy into heat energy, but also improves its viscous acoustic resistance, reduces the grazing flow acoustic impedance and its sensitivity to changes with the grazing flow, better suppresses the grazing flow effect, and forms excellent aviation high-speed grazing flow linear characteristics. Accordingly, this linear acoustic liner can achieve better noise reduction in a wider flow velocity range, while reducing flow resistance and fuel consumption.

[0104] 2) High sound intensity experiments and grazing flow experiments were carried out on the flow tube test bench on the traditional perforated plate acoustic lining and the low flow resistance metal wire mesh composite panel aviation linear acoustic lining. The results of the high sound intensity experiment showed that the low flow resistance metal wire mesh composite panel aviation linear acoustic lining had a better suppression effect on the high sound intensity effect, and the incident sound pressure level of the grazing flow experiment was determined to be 130dB; the results of the grazing flow experiment showed that the low flow resistance metal wire mesh composite panel aviation linear acoustic lining had better linearity for grazing flow than the traditional perforated plate acoustic lining.

[0105] 3) As shown in the optimal acoustic impedance curve, with the increase of Mach number, the optimal acoustic resistance and acoustic reactance of the aero-engine ductor noise reduction decrease and increase respectively, and tend to be stable at high Mach number. At the same time, the acoustic impedance of the low flow resistance metal mesh composite panel aviation linear acoustic lining basically does not change with the sweeping flow within the test range of this experiment, and is closer to the change trend of the optimal acoustic impedance.

[0106] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low flow resistance metal wire mesh composite panel aviation linear sound lining, characterized in that: include: A perforated film, a fine wire mesh and a coarse wire mesh, wherein the perforated film, the fine wire mesh and the coarse wire mesh constitute a composite panel with sound dissipation function; wherein, The perforated film is used to reduce the roughness of the metal wire mesh on the surface of the sound liner, thereby reducing air resistance; The fine mesh is used to provide viscous acoustic resistance, has a sound absorption effect of dissipating sound energy, and reduces the sensitivity of the sound lining performance to high-speed flow and high sound intensity; The coarse wire mesh is used to ensure the structural strength of the composite panel, plays a supporting role, and has an auxiliary sound absorption function.

2. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to claim 1 is characterized in that : The composite panel is used to suppress the sweeping flow effect and reduce the sensitivity of its acoustic performance to the sweeping flow, thereby meeting the optimal acoustic impedance of the aero-engine rear nacelle within a wide flow velocity range and maintaining the sound absorption performance; As well as suppressing the high sound intensity effect and raising the threshold for the occurrence of high sound pressure level effect.

3. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to claim 1, characterized in that: It also includes honeycomb and bottom plate. The perforated film, the coarse wire mesh, the honeycomb and the bottom plate are bonded by adhesive or welding, or, The perforated film, fine wire mesh, honeycomb and bottom plate are bonded by adhesive or welding, or, The perforated film, fine wire mesh, coarse wire mesh, honeycomb and bottom plate are bonded by adhesive or welding; The cross-section of the honeycomb is in the shape of a regular hexagon, a square or a circle.

4. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to claim 2, characterized in that: The fine wire mesh or coarse wire mesh in the composite panel is a microporous panel with drag reduction and dissipation effects, and the thickness of the perforated film in the composite panel is less than 0.2 mm.

5. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to claim 1, characterized in that: The structures of the low flow resistance metal wire mesh composite panel aviation linear sound lining are arranged in the order of the perforated film, the fine wire mesh, the coarse wire mesh, the honeycomb and the bottom plate.

6. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to claim 1, characterized in that: The structures of the low flow resistance metal wire mesh composite panel aviation linear sound liner are arranged in the order of the perforated film, the coarse wire mesh, the fine wire mesh, the honeycomb and the bottom plate.

7. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to claim 1, characterized in that: The structures of the low flow resistance metal wire mesh composite panel aviation linear sound lining are arranged in the order of the perforated film, the fine wire mesh, the coarse wire mesh, the fine wire mesh, the honeycomb and the bottom plate.

8. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to claim 1, characterized in that: By adjusting the perforation rate of the perforated film, the noise reduction condition in a specific noise reduction scenario can be achieved.

9. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to claim 1, characterized in that: By adjusting the number of fine mesh and / or coarse mesh, the noise reduction condition in a specific noise reduction scenario can be achieved.

10. The low flow resistance metal wire mesh composite panel aviation linear acoustic liner according to any one of claims 1 to 9, characterized in that: The low flow resistance metal wire mesh composite panel aviation linear acoustic liner is arranged on the aerodynamic surface of an aircraft engine, an auxiliary power unit, a fuselage, a wing or a horizontal vertical tail.

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