Noise reduction structure, power propulsion system and noise reduction method

Abstract

The invention relates to a noise reduction structure, a power propulsion system and a noise reduction method. Wherein the power propulsion system comprises a first wall surface and a second wall surface, a radial space between the first wall surface and the second wall surface forms an airflow channel of the power propulsion system, the noise reduction structure comprises a plurality of noise reduction units, and each noise reduction unit comprises a groove, a plurality of grooves and a plurality of noise reduction plates, the groove is formed in the surface of at least one of the first wall surface and the second wall surface and is concavely arranged from the surface; the surface provides a wall surface of the airflow channel; and the porous medium layer at least covers the surface of the whole contour line of the groove.

Description

Technical Field

[0001] The invention relates to a noise reduction structure, a power propulsion system and a noise reduction method. Background Art

[0002] The propulsion system, such as the commonly used civil aircraft engine, has a sound radiation level at the airport during takeoff and landing, which is limited by the stringent requirements of the International Civil Aviation Organization (ICAO). The latest airworthiness noise clauses require new civil aircraft to adopt the more stringent fifth-stage noise airworthiness standards, which further reduces the cumulative noise margin by 7dB compared to the fourth-stage. Low-noise design and lightweight design that take into account aerodynamic efficiency are becoming increasingly important in the design stage of new-generation aircraft engine products.

[0003] Aircraft engines are the main noise source of aircraft. In order to obtain excellent thrust performance, the bypass ratio of today's aircraft engines has gradually increased, which has further increased the size of the fan. Due to its large size and high speed, fan noise dominates the engine noise. Therefore, reducing fan noise is the key to aircraft noise reduction design.

[0004] In order to solve the above problems, the existing solution is generally to cover the inner wall of the air inlet and the outer duct with acoustic lining. The working principle of the acoustic lining is to absorb and dissipate the sound waves in the propagation path to achieve the purpose of reducing noise. Honeycomb perforated plate acoustic lining is widely used in today's commercial aircraft engine models. It is mainly composed of a perforated panel, a honeycomb core and a rigid back panel, which can be regarded as a large number of Helmholtz resonance cavities. The size of the resonance cavity determines its resonant frequency. Therefore, sound waves of a specific frequency will resonate after entering the honeycomb core through the small holes on the panel, so that the sound energy is converted into heat energy, achieving the purpose of noise reduction.

[0005] However, due to the need to reduce weight, the design of modern civil turbofan engines shows a trend of increasing bypass ratio and shortening nacelle length. The distance between adjacent blade rows in the duct is shortened, and the position of the wall that can cover the acoustic lining is increasingly limited. Since the sound absorption performance of the acoustic lining is positively correlated with the coverage area of ​​the acoustic lining, the existing means of covering the acoustic lining are difficult to meet the increasingly stringent noise airworthiness standards while meeting the weight reduction needs of the engine. At the same time, the traditional honeycomb perforated plate acoustic lining has a significant effect on single-tone noise reduction due to the principle of frequency resonance. However, fan noise includes single-tone noise and broadband noise, which has multi-target characteristics, and the traditional honeycomb perforated plate acoustic lining configuration performs poorly in multi-frequency noise suppression.

[0006] In summary, the art needs a noise reduction method and a noise reduction method to achieve more efficient broadband noise reduction under conditions of limited space and weight. Summary of the invention

[0007] An object of the present invention is to provide a noise reduction structure.

[0008] Another object of the present invention is to provide a power propulsion system.

[0009] Another object of the present invention is to provide a noise reduction method.

[0010] According to the first aspect of the present invention, a noise reduction structure is provided for a power propulsion system, wherein the power propulsion system comprises: a first wall surface and a second wall surface, wherein the radial space between the first wall surface and the second wall surface constitutes an airflow channel of the power propulsion system, and the noise reduction structure comprises a plurality of noise reduction units, each of the noise reduction units comprises: a groove, wherein the groove is provided on a surface of at least one of the first wall surface and the second wall surface, and is recessed from the surface; the surface provides a wall surface of the airflow channel; and a porous medium layer, at least covering the surface of the entire contour line of the groove.

[0011] In one or more embodiments of the noise reduction structure, the noise reduction unit is distributed in an axial direction including the upstream and / or downstream of the rotor blade corresponding to the airflow channel; and a plurality of the noise reduction units are distributed in a circumferential direction.

[0012] In one or more embodiments of the noise reduction structure, the contour line of the groove includes an arc shape, a square shape, a trapezoid shape, and a star shape.

[0013] In one or more embodiments of the noise reduction structure, the porous medium layer is made of metal material, including foam metal and metal wire mesh.

[0014] In one or more embodiments of the noise reduction structure, the porous medium layer also covers the wall surfaces between adjacent noise reduction units.

[0015] A power propulsion system according to a second aspect of the present invention comprises the noise reduction structure as described in the first aspect.

[0016] In one or more embodiments of the power propulsion system, the power propulsion system includes a turbofan engine, and the noise reduction structure is arranged on the inner surface of the fan case, the inner wall of the air inlet nacelle, the outer duct outlet wall, and / or the fan hub surface of the turbofan engine.

[0017] In one or more embodiments of the power propulsion system, the noise reduction unit and the first wall and / or the second wall where it is located are formed as an integral part.

[0018] According to a noise reduction method of a third aspect of the present invention, the power propulsion system comprises: a first wall surface and a second wall surface, and the radial space between the first wall surface and the second wall surface constitutes an airflow channel of the power propulsion system. The noise reduction method comprises:

[0019] A noise reduction structure is directly arranged on the surface of the first wall surface and / or the second wall surface, and the noise reduction structure includes a plurality of noise reduction units, each of which includes: a groove, which is opened on the surface of at least one of the first wall surface and the second wall surface and is recessed from the surface; the surface provides the wall surface of the airflow channel; and a porous medium layer, which at least covers the surface of the contour line of the groove.

[0020] In one or more embodiments of the noise reduction method, the noise reduction structure is arranged in an axial distribution range upstream and / or downstream of the rotor blade corresponding to the airflow channel; and a plurality of the noise reduction units are distributed circumferentially so that the noise reduction units are staggered with the axial regions corresponding to the rotor blades.

[0021] In one or more embodiments of the noise reduction method, the noise reduction unit is configured to directly serve as the wall of the airflow channel and directly contact the airflow of the airflow channel, and a silent lining is arranged on the surface of the first wall and the second wall.

[0022] In one or more embodiments of the noise reduction method, noise reduction units with different structures at different axial positions include a first noise reduction unit and a second noise reduction unit, and the acoustic impedance value of the porous medium layer, the shape, size and / or number of axial distribution of the grooves of the first noise reduction unit and the second noise reduction unit are different.

[0023] The beneficial effects of the present invention include, but are not limited to, compared to the noise reduction scheme of setting a sound liner on the engine wall, the noise reduction structure and noise reduction method adopted in this case not only meet the requirements of weight reduction on the basis of noise reduction effect, but also further improve the noise reduction effect. The principle is that compared to the straight wall configuration formed by setting a sound liner, the groove structure significantly increases the contact area between the sound absorbing material and the sound field, thereby achieving more sound energy dissipation. At the same time, sound waves will produce irregular scattering in the groove, and each scattering will increase the number of contacts with the sound absorbing material. In addition, due to the porous medium material covering the surface of the groove, there are micro-scale cavities of different sizes inside the material, which can dissipate sound waves of different frequencies, so compared with the current sound liner scheme, it also has the characteristics of broadband sound absorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments, in which:

[0025] Figure 1 It is a schematic diagram of the existing noise reduction solution for gas turbine engines.

[0026] Figure 2 It is a schematic structural diagram of a power propulsion system of an embodiment from an external perspective.

[0027] Figure 3 It is a structural schematic diagram of a power propulsion system of an embodiment from a cross-sectional perspective.

[0028] FIG. 4A to FIG. 4D The schematic diagrams of the structures of the noise reduction units of the noise reduction structures of the first embodiment, the second embodiment, the third embodiment and the fourth embodiment are respectively.

[0029] Figure 5A , Figure 5B , Figure 5C The sound pressure contours corresponding to the sound propagation numerical calculation of the wall surface without noise reduction, the wall surface of the acoustic lining component and the noise reduction structure of the first embodiment are shown respectively.

[0030] Reference numerals for parts:

[0031] 100-Power Propulsion System

[0032] 101-First wall

[0033] 102-Second wall

[0034] 1000-Airflow Channel

[0035] 1003-Inner surface of fan casing

[0036] 1004-Inlet nacelle inner wall

[0037] 1005-External duct outlet wall

[0038] 1006-Fan hub surface

[0039] 10000- Acoustic Lining

[0040] 10-Noise reduction structure

[0041] 1001-Noise reduction unit

[0042] 1-Groove

[0043] 2-Porous medium layer. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with specific embodiments and drawings. More details are elaborated in the following description to facilitate a full understanding of the present invention. However, the present invention can obviously be implemented in a variety of other ways different from the description herein. Those skilled in the art can make similar generalizations and deductions based on actual application situations without violating the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0045] At the same time, the present application uses specific words to describe the embodiments of the present application, such as "one embodiment", "an embodiment", and / or "some embodiments" to refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" mentioned twice or more in different locations in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0046] The noise reduction structure and noise reduction method introduced in the following embodiments are applied to gas turbine engines, specifically taking a turbofan engine as an example, but not limited to this. It can be applicable to any power propulsion system, including a power propulsion system with a fan, blades, propeller fans, etc. It is not limited to gas turbine engines. For example, it can be a hybrid propulsion system including a gas turbine engine, or a pure electric drive power propulsion system with a fan, blades, and propeller fans. As long as the fan noise and / or the intake noise of the compressor are reduced, the noise reduction structure of this case can be applied.

[0047] Existing solutions include Figure 1 As shown, the fan of the gas turbine engine includes fan rotor blades 18 and fan stator blades 20. Acoustic lining members 10000 can be provided on the inner wall surface 1004 of the air inlet nacelle and the inner surface 1003 of the fan casing to absorb and attenuate the sound energy of single-tone noise, while broadening the sound absorption frequency band as much as possible to take into account broadband.

[0048] However, the inventors have found that the use of acoustic linings for noise reduction is not conducive to reducing the weight of the engine, and the broadband noise reduction performance of the acoustic linings is also relatively insufficient.

[0049] Based on the above, the inventors have invented a new noise reduction structure, a power propulsion system and a noise reduction method. Compared with the noise reduction scheme of setting a sound liner on the engine wall, the noise reduction structure and noise reduction method adopted in this case not only meet the requirements of weight reduction on the basis of noise reduction effect, but also further improve the noise reduction effect. The principle is that compared with the straight wall configuration formed by setting a sound liner, the groove structure significantly increases the contact area between the sound absorbing material and the sound field, thereby achieving more sound energy dissipation. At the same time, sound waves will produce irregular scattering in the groove, and each scattering will increase the number of contacts with the sound absorbing material. In addition, due to the porous medium material covering the surface of the groove, there are micro-scale cavities of different sizes inside the material, which can dissipate sound waves of different frequencies, so compared with the current sound liner scheme, it also has the characteristics of broadband sound absorption.

[0050] refer to Figure 2 as well as Figure 3As shown, in some embodiments, the turbofan engine may include an air inlet 15, a noise reduction structure 10, a fan hub 17, a fan rotor blade 18, a nacelle 19, a fan stator blade 20, a low-pressure compressor blade 21, a high-pressure compressor blade 22, a turbine blade 23, an exhaust duct 24, and an outer duct 25. The noise reduction structure 10 may be provided on the inner surface 1003 of the fan casing, the inner wall surface 1004 of the air inlet nacelle, the outer duct outlet wall surface 1005, and / or the fan hub surface 1006 to reduce the noise caused by the fan.

[0051] refer to Figure 2 , Figure 3 as well as FIG. 4A to FIG. 4D As shown, the noise reduction structure 10 includes a plurality of noise reduction units 1001, each of which includes: a groove 1 and a porous medium layer 2, wherein the groove 1 is opened on the surface of at least one of the first wall 101 and the second wall 102, and is recessed from the surface; the surface provides the wall surface of the air flow channel 1000; the porous medium layer 2 at least covers the surface of the contour line of the groove 1.

[0052] In the power propulsion system, the radial space between the first wall 101 and the second wall 102 constitutes the specific structure of the airflow channel 1000 of the power propulsion system, for example, the inner wall 1004 of the air inlet nacelle and the fan hub surface 1006 constitute the air inlet channel, for example, the inner surface 1003 of the fan casing and the outer duct outlet wall 1005 constitute part of the outer duct, but it is not limited to this.

[0053] Here, the surface of the contour line of the groove 1 means, FIG. 4A to FIG. 4D As shown, taking the cross section of the groove 1 as an example, the porous medium layer 2 at least covers all the concave parts of the groove 1, as shown in FIG. Figure 4A In the first embodiment shown, the contour line of the cross section of the arc 11 is such that the porous medium layer 2 covers the entire arc. Figure 4B In the second embodiment shown, the outline of the cross section of the square 12 is that the porous medium layer 2 covers the groove wall and the groove bottom of the groove. Figure 4C In the third embodiment shown, the outline of the cross section of the trapezoidal shape 13 is such that the porous medium layer 2 covers the groove wall and the groove bottom of the groove. Figure 4D In the fourth embodiment shown, the outline of the cross section of the star 14 is such that the porous medium layer 2 covers the entire star, including the protruding portion of the star.

[0054] The porous medium material of the porous medium layer 2 is generally a metal material, so it is easy to be set in the groove. The porous medium layer of the metal material can be in the form of foam metal, wire mesh, such as foam aluminum, foam copper, foam nickel, foam alloy, etc. The wire mesh, as the name implies, is a mesh-shaped metal film. It can be understood that the porous medium material can also be other porous medium materials with broadband sound absorption performance. Preferably, in some embodiments, in addition to being set on the surface of the entire contour line of the groove 1, the porous medium layer 2 can also cover the space between the grooves, that is, the wall surface between adjacent noise reduction units 1001, that is, covering the wall surface of the first wall surface or the second wall surface itself.

[0055] The noise reduction unit 1001 is arranged on the first wall surface 101 and / or the second wall surface 102. The noise reduction unit 1001 and the first wall surface 101 and / or the second wall surface 102 where the noise reduction unit 1001 is located are an integrally formed part. The specific process can be obtained by additive manufacturing so as to obtain the integral part. This can further simplify the process. For a turbofan engine, for example, for the processing and manufacturing of a fan case, it saves the processing step of setting a sound lining member on the inner surface 1003 of the fan case after the processing of the fan case is completed.

[0056] Continue to refer Figure 2 as well as Figure 3 As shown, the noise reduction unit 1001 includes the upstream and / or downstream of the rotor blade 1002 corresponding to the airflow channel 1000 in the axial distribution range, and the noise reduction unit 1001 is staggered in the axial area corresponding to the tip of the rotor blade 1002. The beneficial effect of this is that it can prevent the groove structure from acting on the tip of the rotor blade to change the distribution of the unsteady force on the blade surface, which causes the noise to increase. In addition, within a certain axial range, multiple noise reduction units 1001 are evenly distributed circumferentially. It can be understood that the arrangement of the arrangement and combination formed by multiple noise reduction units 1001 can be regular or irregular. The porous medium can be equivalent to an impedance soft boundary through sound propagation calculation, and the design is optimized through iteration. A design scheme with maximum transmission loss is obtained. The optimization goal is the maximum transmission loss of the sound mode that the fan can conduct, and the optimized parameters are the impedance value of the porous material laid on the groove wall and the groove gap wall, the shape of the groove, the size of the groove, and the distribution of the groove. Through the obtained optimal impedance value, the parameters of the porous material are obtained based on the impedance model, thereby realizing the design of the silencing wall.

[0057] The noise reduction structure 10 of the above embodiment has a weight reduction effect compared to the solution of the acoustic lining member, and has better broadband sound absorption characteristics. FIG. 5A to FIG. 5CAs shown, a circular tube of equal diameter is used to simulate the sound propagation process of fan noise in the air inlet. The diameter of the pipe is 1m, the length of the acoustic impedance boundary is 1.1m, and its distance from the pipe inlet and outlet is 0.1m. The pipe inlet is the sound source surface, and the sound source incident mode is (5, 1). The pipe outlet is a non-reflecting boundary. The background flow is a uniform average flow with a flow velocity of 170m / s and a flow direction pointing to the sound source surface. An impedance boundary is applied to the pipe wall to simulate the sound absorption characteristics of porous media materials. Three configuration examples are used:

[0058] In the first example, the admittance value of the impedance boundary is 0, that is, it is a light wall, that is, for example, the inner surface 1003 of the existing fan casing.

[0059] The admittance value of the impedance boundary of Example 2 is 0.0012+0.0012j, and there is no groove on the surface, which represents a traditional straight noise reduction wall, that is, for example, a structure in which an acoustic lining member 10000 is provided on the inner surface 1003 of the fan casing in the existing solution.

[0060] The admittance value of the impedance boundary in Example 3 is the same as that in Example 2, but there is a circular groove on the surface, that is, Figure 4A The structure of the groove of the first embodiment is shown to simplify the noise reduction wall configuration of the present invention.

[0061] Based on the finite element Helmholtz method, the sound propagation calculation of the example is carried out, and the calculation results of the sound pressure cloud map are shown in Figure 4. It can be observed that laying the impedance wall can achieve sound energy dissipation. At the same time, the sound field of the groove noise reduction wall design is significantly different from that of the straight noise reduction wall design. The transmission loss calculation results of the three configurations are 0dB, 14dB, and 16dB, respectively. Therefore, the groove noise reduction wall of the present invention has an excellent noise reduction effect, and the noise reduction amount is greater than the traditional straight wall configuration.

[0062] In summary, the beneficial effects of adopting the above embodiments include but are not limited to, compared with the noise reduction solution of setting a sound liner on the engine wall, the noise reduction structure and noise reduction method adopted in this case meet the requirements of weight reduction on the basis of the noise reduction effect, and because the porous medium material covers the surface of the groove, there are micro-scale cavities of different sizes inside the material, which can dissipate sound waves of different frequencies, and thus compared with the current sound liner solution, it also has the characteristics of broadband sound absorption.

[0063] As described above, the present application further provides a noise reduction method for a power propulsion system. The power propulsion system 100 includes: a first wall surface 101 and a second wall surface 102. The radial space between the first wall surface 101 and the second wall surface 102 constitutes an airflow channel 1000 of the power propulsion system. The noise reduction method includes:

[0064] A noise reduction structure 10 is directly arranged on the surface of the first wall 101 and / or the second wall 102, and the noise reduction structure 10 includes a plurality of noise reduction units 1001, and each noise reduction unit 1001 includes: a groove 1, which is opened on the surface of at least one of the first wall 101 and the second wall 102 and is arranged recessed from the surface; the surface provides the wall surface of the air flow channel 1000; and a porous medium layer 2, which at least covers the surface of the contour line of the groove 1.

[0065] Preferably, in some embodiments, the noise reduction structure 10 is arranged in the axial distribution range to be upstream and / or downstream of the rotor blade 1002 corresponding to the airflow channel 1000; and a plurality of noise reduction units 1001 are distributed in the circumferential direction so that the noise reduction units 1001 are staggered from the axial regions corresponding to the rotor blade 1002. This avoids the risk of increased noise caused by the interaction between the groove and the rotor blade tip.

[0066] Preferably, in some embodiments, the noise reduction unit 1001 is configured to directly serve as the wall of the airflow channel 1000 and directly contact the airflow of the airflow channel, and a silent lining is provided on the surface of the first wall 101 and the second wall 102. It can be understood that the noise reduction effect of the noise reduction structure 10 is better than that of the acoustic lining. Therefore, the silent lining will not affect the noise reduction effect and also achieves weight reduction of the engine.

[0067] Preferably, in some embodiments, as described above, noise reduction in different frequency bands can be achieved by changing the structure of the grooves and the impedance of the porous medium layer, for example, noise reduction units with different sound barriers are set in regions of different axial lengths, that is, for example, noise reduction units 1001 with different structures at different axial positions, including a first noise reduction unit and a second noise reduction unit, wherein the acoustic impedance value of the porous medium layer 2, the shape, size and / or number of axial distribution of the grooves 1 of the first noise reduction unit and the second noise reduction unit are different. The first noise reduction unit and the second noise reduction unit mentioned above are only to indicate the difference in structure between the noise reduction units, and are not limited to two different noise reduction units.

[0068] In summary, the beneficial effects of the noise reduction structure, power propulsion system and noise reduction method introduced in the above embodiments include but are not limited to, compared with the noise reduction scheme of setting a sound lining on the engine wall, the noise reduction structure and noise reduction method adopted in this case not only meet the requirements of weight reduction on the basis of noise reduction effect, but also further improve the noise reduction effect. The principle is that compared with the straight wall configuration formed by setting a sound lining, the groove structure significantly increases the contact area between the sound absorbing material and the sound field, thereby achieving more sound energy dissipation. At the same time, the sound waves will produce irregular scattering in the groove, and each scattering will increase the number of contacts with the sound absorbing material. In addition, due to the porous medium material covering the surface of the groove, there are micro-scale cavities of different sizes inside the material, which can dissipate sound waves of different frequencies, so compared with the current sound lining scheme, it also has the characteristics of broadband sound absorption.

[0069] Although the present invention is disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. A noise reduction structure (10) for a power propulsion system (100), wherein: The power propulsion system (100) comprises: a first wall surface (101) and a second wall surface (102), wherein a radial space between the first wall surface (101) and the second wall surface (102) constitutes an airflow channel (1000) of the power propulsion system, and is characterized in that the noise reduction structure (10) comprises a plurality of noise reduction units (1001), and each of the noise reduction units (1001) comprises: A groove (1), the groove (1) being opened on a surface of at least one of the first wall surface (101) and the second wall surface (102), and being arranged recessed from the surface; the surface providing a wall surface of the airflow channel (1000); and The porous medium layer (2) at least covers the surface of the entire contour line of the groove (1).

2. The noise reduction structure (10) according to claim 1, characterized in that: The noise reduction unit (1001) has an axial distribution range including the upstream and / or downstream of the rotor blade (18) corresponding to the airflow channel (1000); and a plurality of the noise reduction units (1001) are distributed circumferentially.

3. The noise reduction structure (10) according to claim 1, characterized in that: The contour line of the groove (1) includes arc, square, trapezoid and star shapes.

4. The noise reduction structure (10) according to claim 1, characterized in that: The material of the porous medium layer (2) is a metal material, including foam metal and metal wire mesh.

5. The noise reduction structure (10) according to claim 1, characterized in that: The porous medium layer (2) also covers the wall surfaces between adjacent noise reduction units (1001).

6. A power propulsion system (100), characterized in that: It comprises the noise reduction structure (10) as claimed in any one of claims 1 to 5.

7. The propulsion system (100) according to claim 6, characterized in that: The power propulsion system includes a turbofan engine, and the noise reduction structure (10) is arranged on the inner surface (1003) of the fan casing, the inner wall surface (1004) of the air inlet nacelle, the outer duct outlet wall surface (1005), and / or the fan hub surface (1006) of the turbofan engine.

8. The propulsion system (100) according to claim 6, characterized in that: The noise reduction unit (1001) and the first wall surface (101) and / or the second wall surface (102) on which it is located are integrally formed.

9. A noise reduction method for a power propulsion system (100), wherein: The power propulsion system (100) comprises: a first wall surface (101) and a second wall surface (102), wherein a radial space between the first wall surface (101) and the second wall surface (102) constitutes an airflow channel (1000) of the power propulsion system, and is characterized in that the noise reduction method comprises: A noise reduction structure (10) is directly arranged on the surface of the first wall surface (101) and / or the second wall surface (102), wherein the noise reduction structure (10) comprises a plurality of noise reduction units (1001), each of the noise reduction units (1001) comprising: a groove (1), the groove (1) being opened on the surface of at least one of the first wall surface (101) and the second wall surface (102), and being arranged recessed from the surface; the surface providing the wall surface of the airflow channel (1000); and a porous medium layer (2), at least covering the surface of the contour line of the groove (1).

10. The noise reduction method according to claim 9, characterized in that: The noise reduction structure (10) is arranged in an axial distribution range upstream and / or downstream of the rotor blade (18) corresponding to the airflow channel (1000); and a plurality of the noise reduction units (1001) are distributed circumferentially so that the noise reduction units (1001) are staggered with the axial regions corresponding to the rotor blade (18).

11. The noise reduction method according to claim 9, characterized in that: The noise reduction unit (1001) is configured to directly serve as a wall surface of the airflow channel (1000) and directly contact the airflow of the airflow channel, and a silent lining is provided on the surface of the first wall surface (101) and the second wall surface (102).

12. The noise reduction method according to claim 9, characterized in that: Noise reduction units (1001) with different structures at different axial positions include a first noise reduction unit and a second noise reduction unit, wherein the acoustic impedance value of the porous medium layer (2), the shape, size and / or number of axial distribution of the grooves (1) of the first noise reduction unit and the second noise reduction unit are different.

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