Acoustic attenuation panel for aircraft turbomachinery

Abstract

Acoustic attenuation panel for aircraft turbomachinery. The present invention relates to an acoustic attenuation panel (1) comprising: - a first honeycomb structure (2) comprising peripheral walls (8) and a plurality of acoustic cells (4), each acoustic cell (4) comprising a cavity (6) delimited by several of the peripheral walls (8), - a second honeycomb structure (16) comprising peripheral walls (24) and a plurality of acoustic cells (20), each acoustic cell (20) comprising a cavity (22) delimited by several of the peripheral walls (24), wherein the peripheral walls (24) of the second honeycomb structure (16) each have a thickness less than or equal to 1 mm and a density less than or equal to 100 kg / m3. Figure for the abstract: Fig. 1.

Description

Title of the invention: Acoustic attenuation panel for aircraft turbomachinery technical field

[0001] The invention relates to the field of acoustic attenuation panels for aircraft turbomachinery. Previous technique

[0002] An aircraft turbomachine typically has a longitudinal axis. It includes, for example, from upstream to downstream in the direction of gas flow along the longitudinal axis, a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, a low-pressure turbine, and a gas exhaust nozzle.

[0003] The blower allows the intake of an airflow that splits into a primary flow and a secondary flow. The primary flow passes through a primary channel of the turbomachine while the secondary flow is directed towards a secondary channel surrounding the primary channel.

[0004] The primary flow is compressed within the compressors. The compressed air is then mixed with a fuel and burned within the combustion chamber. The gases from the combustion pass through the turbines and then escape through the nozzle, the cross-section of which allows these gases to be accelerated to generate propulsion.

[0005] The blower typically comprises a rotating disc about its longitudinal axis and blades mounted on the disc. The blades are surrounded by a blower housing centered on the longitudinal axis and designed to retain the blades in case of damage, for example, to the blades.

[0006] The fan housing is typically surrounded by a nacelle that protects the fan. Such a fan is said to be enclosed, as opposed to unenclosed fans whose blades are not surrounded by a housing.

[0007] The turbomachine further comprises an intermediate casing located downstream of the blower casing and defining a portion of the secondary flow.

[0008] Turbomachinery is a significant source of noise pollution, and there is a strong demand to reduce this type of pollution. Furthermore, given the evolution of turbomachinery configurations, the rotational speed of the fans tends to decrease. However, the slower the rotational speed, the lower the frequencies of the generated sound waves. Moreover, the sound waves generated by turbomachinery can span a wide frequency range.

[0009] To this end, it has been proposed to equip certain components of the turbomachine such as the fan and intermediate casing and / or the nacelle with acoustic panels in order to reduce the noise generated by the turbomachines.

[0010] An acoustic panel typically comprises a honeycomb structure including acoustic cells forming Helmholtz resonators. Each acoustic cell includes a peripheral wall extending in a direction parallel to the propagation of sound waves within that cell. Each acoustic cell further includes a cavity delimited by the peripheral wall and within which the sound waves propagate. Such an acoustic panel is, for example, known from document FR3102882A1.

[0011] The number of honeycomb structures in the acoustic panel determines the acoustic performance of the acoustic panel with regard to the frequency range of sound waves that the acoustic panel is capable of attenuating. Indeed, depending on the number of honeycomb structures in the acoustic panel, the frequency spectrum of noise attenuation is more or less significant.

[0012] Acoustic panels with a single degree of freedom, known by the English acronym SDOF for "Single Degree of Freedom," and acoustic panels with two degrees of freedom, known by the English acronym DDOF for "Double Degree of Freedom," are known. A DDOF acoustic panel, as opposed to an SDOF acoustic panel, comprises first and second honeycomb structures separated by a membrane permeable to sound waves. Each honeycomb structure is thus capable of attenuating sound waves over a specific and distinct frequency range. Such a configuration of the acoustic panel makes it possible to broaden the frequency range of the attenuated sound waves.

[0013] Today, there is a need to provide an acoustic panel that is lighter and less expensive than those offered in the prior art. Description of the invention

[0014] The invention aims in particular to overcome at least partially one of these drawbacks and relates, according to a first aspect, to a sound attenuation panel comprising:

[0015] a first alveolar structure comprising peripheral walls and a plurality of acoustic cells, each acoustic cell comprising a cavity delimited by several of the peripheral walls,

[0016] a second alveolar structure comprising an acoustically permeable membrane, peripheral walls and a plurality of acoustic cells, each acoustic cell comprising a cavity delimited by several of the peripheral walls.

[0017] For example, the peripheral walls of the second alveolar structure each have, for example, a thickness less than or equal to 1 mm and a density less than or equal to 100 kg / m3.

[0018] Thanks to the peripheral walls of the second honeycomb structure having such thickness and density, the mass of the second honeycomb structure is reduced and therefore the overall mass of the acoustic attenuation panel.

[0019] According to other features of the invention, the acoustic attenuation panel of the invention includes one or more of the following optional features.

[0020] For example, the peripheral walls of the second alveolar structure are made of thermoplastic film, for example include a thermoplastic film material, for example are formed of a material comprising a thermoplastic film.

[0021] For example, the peripheral walls of the second alveolar structure are made of paper, for example include a paper material, for example are formed of a paper material.

[0022] For example, the acoustic attenuation panel includes an acoustically permeable membrane.

[0023] For example, the membrane has a thickness less than or equal to 1 mm and a density less than or equal to 100 kg / m3.

[0024] For example, the acoustically permeable membrane is made of thermoplastic film, for example comprises a thermoplastic film material, for example is formed of a thermoplastic film material.

[0025] For example, the acoustically permeable membrane is made of paper, for example comprises a paper material, for example is formed from a paper material.

[0026] Thus, the acoustically permeable membrane and the peripheral walls of the second alveolar structure each have, for example, a thickness less than or equal to 1 mm and a density less than or equal to 100 kg / m3.

[0027] Thanks to the acoustically permeable membrane and the peripheral walls of the second honeycomb structure having such thickness and density, the mass of the second honeycomb structure is reduced and therefore the overall mass of the acoustic attenuation panel, in particular double degree of freedom (DDOF) panels.

[0028] For example, the second alveolar structure includes the acoustically permeable membrane.

[0029] For example, the acoustically permeable membrane extends to a base of the peripheral walls of the second alveolar structure.

[0030] For example, the acoustically permeable membrane can extend into the cavity of the acoustic cells of the second alveolar structure, for example between the base and the top of the peripheral walls of the second alveolar structure.

[0031] For example, the acoustically permeable membrane can extend into the cavity of the acoustic cells of the first alveolar structure, for example between a base and an apex of the peripheral walls of the first alveolar structure.

[0032] For example, some, for example at least some, of the peripheral walls of the second alveolar structure have a housing provided in a base of these walls and complementary to a top of the peripheral walls of the first alveolar structure so as to allow the second alveolar structure to be fitted onto the first alveolar structure.

[0033] For example, some, for example at least some, of the peripheral walls of the first alveolar structure have a housing provided in a vertex of these walls and complementary to a base of the peripheral walls of the second alveolar structure so as to allow the second alveolar structure to be fitted onto the first alveolar structure.

[0034] For example, some, for example at least some, of the walls of the second honeycomb structure have different heights, for example from each other. For example, some, for example at least some, of the walls of the second honeycomb structure each have a different height.

[0035] For example, the second alveolar structure comprises more peripheral walls than the first alveolar structure.

[0036] For example, the second alveolar structure includes additional peripheral walls, for example compared to the first alveolar structure.

[0037] For example, some, for example at least some, for example all the additional peripheral walls have different heights, for example from each other. For example, some, for example at least some, for example all the additional peripheral walls each have a different height.

[0038] For example, certain peripheral walls of the second alveolar structure, for example the additional peripheral walls of the second alveolar structure are arranged so as to extend into both the first alveolar structure and the second alveolar structure.

[0039] For example, certain peripheral walls of the second alveolar structure, for example certain additional peripheral walls of the second alveolar structure, extend from a first face of the acoustically permeable membrane and other peripheral walls, for example other additional peripheral walls, of the second alveolar structure extend from a second face of the acoustically permeable membrane, for example so that some acoustic cells of the second alveolar structure extend into the cavity of some acoustic cells of the first alveolar structure.

[0040] For example, the acoustically permeable membrane and at least some of the peripheral walls of the second alveolar structure, for example the additional peripheral walls, are formed by folding a material, for example of the same material, for example so that said peripheral walls extend transversely, for example orthogonally, with respect to the acoustically permeable membrane.

[0041] According to one aspect, the invention relates to an aircraft turbomachine comprising an acoustic attenuation panel as previously described.

[0042] According to one aspect, the invention relates to an aircraft nacelle comprising an acoustic panel as previously described. Brief description of the drawings

[0043] [Fig-1] The [Fig. 1] is a perspective representation of an acoustic attenuation panel according to an embodiment of the invention.

[0044] [Fig.2] The [Fig.2] is a cross-sectional representation of part of the acoustic panel illustrated in the [Fig.1].

[0045] [Fig.3] The [Fig.3] is a perspective representation of an acoustic attenuation panel according to an embodiment of the invention.

[0046] [Fig.4] The [Fig.4] is a cross-sectional representation of part of the acoustic attenuation panel illustrated in the [Fig.3].

[0047] [Fig.5] The [Fig.5] is a cross-sectional representation of part of an acoustic attenuation panel according to an alternative embodiment.

[0048] [Fig.6] The [Fig.6] is a perspective representation of acoustic cells of an acoustic attenuation panel according to the invention.

[0049] [Fig.7] The [Fig.7] is a cross-sectional representation of part of an acoustic attenuation panel according to an alternative embodiment.

[0050] [Fig.8] The [Fig.8] is a cross-sectional representation of part of an acoustic attenuation panel according to an alternative embodiment.

[0051] [Fig.9] The [Fig.9] is a cross-sectional representation of part of an acoustic attenuation panel according to an alternative embodiment.

[0052] [Fig. 10] The [Fig. 10] is a perspective representation of an acoustic attenuation panel according to an embodiment of the invention.

[0053] [Fig. 11] The [Fig. 11] is a longitudinal cross-sectional view of a propulsion assembly comprising a turbomachine, a nacelle and at least one acoustic attenuation panel according to the invention. Description of the implementation methods

[0054] In the remainder of the description of the acoustic attenuation panel according to the invention, the same numerical references designate the same elements.

[0055] Examples of acoustic attenuation panel 1 according to the invention are shown in Figures 1 to 10. The attenuation panel 1 is advantageously an acoustic attenuation panel for an aircraft turbomachine or nacelle as illustrated in [Fig. 11].

[0056] The acoustic attenuation panel 1 advantageously has a sandwich structure.

[0057] The acoustic attenuation panel 1 comprises a first honeycomb structure 2 comprising peripheral walls 8 and a plurality of acoustic cells 4, each acoustic cell may comprise a cavity 6 delimited by several peripheral walls.

[0058] The acoustic attenuation panel 1 may include an aeroacoustic layer 10, 12.

[0059] According to a first embodiment, the aeroacoustic layer 10, 12 may comprise a perforated structure, for example only. The perforated structure may have holes with a diameter of between 0.5 and 2 mm and an acoustic openness ratio of approximately 8 to 18%.

[0060] According to another embodiment, the aeroacoustic layer 12 may comprise a structure, for example thin, acoustically permeable and resistive, for example only. The thin structure may comprise, for example, a micro-perforated film, or comprise, for example, a porous layer 12 such as an acoustically porous fabric or mesh.

[0061] In the examples illustrated in Figures 1 and 3, the aeroacoustic layer may include the acoustically permeable and resistive structure, for example a porous layer 12 and / or a plurality of ribs 10 forming macro s-orifices s.

[0062] As illustrated in Figures 1 and 3, the plurality of ribs 10 can be located between the first alveolar structure 2 and the porous layer 12.

[0063] For example, the plurality of ribs 10 can form a plurality of orifices, extending in two directions, for example coplanar. The number of orifices can vary in the two directions.

[0064] For example, the plurality of ribs 10 and the first alveolar structure 2 can be formed in a single piece, i.e. made in one piece.

[0065] The porous layer 12 can be fixed to the plurality of ribs 10 by an entanglement of the respective materials of the porous layer 12 and the plurality of ribs 10.

[0066] By entanglement we mean a diffusion of material into another material, a penetration of material to create bridges of material between the components.

[0067] According to one embodiment of the invention, the first alveolar structure 2, the plurality of ribs 10 and the porous layer 12 comprise an identical material.

[0068] According to a first example, the first alveolar structure 2, the plurality of ribs 10 and the porous layer 12 comprise a metallic material such as aluminium, in particular an aluminium alloy selected from the 6000 series.

[0069] The porous layer 12 can be, for example, a micro-perforated metal sheet, for example by a micro-perforation technique carried out by laser so as to form a layer similar to a mesh.

[0070] In one embodiment, the porous layer 12 can be a very fine aluminum alloy mesh from the same series or from a compatible alloy series such as an alloy selected from the 5000 series.

[0071] According to a second example, the first alveolar structure 2, the plurality of ribs 10 and the porous layer 12 comprise a composite material, preferably a material formed of a thermoplastic or thermosetting matrix which can be reinforced with fibers such as, for example, glass or carbon fibers.

[0072] According to another embodiment of the invention, the first honeycomb structure 2, the plurality of ribs 10, and the porous layer 12 comprise a different material. For example, the first honeycomb structure 2 and the plurality of ribs 10 comprise a composite material, and the porous layer 12 comprises a metallic material.

[0073] Preferably, the plurality of ribs 10 and the peripheral walls 8 of the first honeycomb structure each have a thickness between 0.5 and 5 mm. For example, the plurality of ribs 10 have a thickness between 0.5 and 2 mm, and the peripheral walls 8 each have a thickness between 1 and 5 mm, more preferably between 1 and 3 mm. The first honeycomb structure 2 thus formed provides sufficient stiffness and rigidity for the entire acoustic attenuation panel.

[0074] As illustrated in Figures 1 to 10, the acoustic attenuation panel 1 may include a second honeycomb structure 16. The second honeycomb structure 16 may include peripheral walls 24 and a plurality of acoustic cells 20, each acoustic cell may include a cavity 22 delimited by several of the peripheral walls 24.

[0075] The second alveolar structure 16 can be superimposed on the first acoustic alveolar structure 2. The first alveolar structure 2 can extend between the aeroacoustic layer and the second alveolar structure 16.

[0076] The peripheral walls 24 of the second alveolar structure 16 can each have a thickness less than or equal to 1 mm, for example between 0.05 and 1 mm, for example between 0.1 and 0.5 mm, and a density less than or equal to 100 kg / m3, preferably less than or equal to 60 kg / m3, even more preferably less than or equal to 40 kg / m3.

[0077] Advantageously, the peripheral walls 24 have a thickness between 0.05 and 0.8 mm, for example between 0.1 and 0.5 mm.

[0078] By providing peripheral walls 24 of the second honeycomb structure 16 with such thickness and such density, the mass of the second honeycomb structure 16 is reduced and therefore the overall mass of the acoustic attenuation panel 1.

[0079] Alternatively, the peripheral walls 24 of the second alveolar structure 16 may each have a density less than or equal to 100 kg / m3, for example less than or equal to 60 kg / m3, for example less than or equal to 40 kg / m3.

[0080] Alternatively, the peripheral walls 24 of the second alveolar structure 16 may each have a thickness less than or equal to 1 mm, for example between 0.05 mm and 1 mm, for example less than 0.5 mm.

[0081] For example, the density of the walls may be less than 3, for example less than 2.

[0082] According to the invention, the first honeycomb structure 2 provides the stiffness to the acoustic panel, and the second honeycomb structure 16 provides the additional partitions required acoustically and makes it possible to obtain an acoustic panel whose overall mass is much lighter than those of the acoustic attenuation panels with several honeycomb structures provided by the prior art.

[0083] For example, the peripheral walls 24 of the second alveolar structure 16. These can be formed from a film, for example, a thin film. The film can be made of a material comprising, for example, a thermoplastic polymer, for example, based on poly(ethylene terephthalate) (PET), polyamides (PA), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyetherimide (PEI), polyetheretherketone (PEEK), or a thermosetting material, for example, epoxy, phenolic resin, or polyimide. The material can, for example, be reinforced with short fibers of glass, carbon, aramid, basalt, or ceramic (preferably at volume percentages between 15% and 40%). The film can, for example, be in the form of a thin layer with a thickness between 0.05 mm and 1 mm.

[0084] For example, the peripheral walls 24 of the second honeycomb structure 16 can be formed of a paper material, for example, include a paper material, for example, are made of paper. By paper is meant a fibrous texture of fibers discontinuous layers arranged in a plane to form a thin layer. The paper can be made of cellulose fibers, mineral fibers (including, for example, glass fibers), or organic fibers (including, for example, aramid or carbon fibers). It can be in the form of strips or sheets with a surface mass between 50 g / m² and 300 g / m². For example, the paper can be coated with one or more layers of baked thermosetting resin or thermoplastic polymer, for example, to increase the stiffness of the membrane and walls.

[0085] The use of these materials makes it possible to provide a second alveolar structure that is even lighter, due to their surface mass.

[0086] In another example, the peripheral walls of the second honeycomb structure can be formed from thin aluminum strips.

[0087] In the examples shown, and as is particularly visible in Figures 2, 4 and 5, 7 and 10, the peripheral walls 24 of the second alveolar structure 16 may have a recess 26, for example a groove, a channel or a slot formed, for example, in the base of these walls 24. By base 240 of the walls is meant the first ends of the walls, for example proximal to the first alveolar structure 2. The walls may also have a vertex 246, corresponding, for example, to the opposite end of these walls, for example distal to the first alveolar structure 2. The base 240 of these peripheral walls 24 is intended to engage with a vertex 80 of the peripheral walls 8 of the first alveolar structure 2 when the second alveolar structure 16 is superimposed on the first alveolar structure 2.Each housing 26 can be complementary to a vertex 80 of the peripheral walls 8 of the first honeycomb structure 2 so as to allow the second honeycomb structure 16 to be fitted onto the first honeycomb structure 2. Each housing 26 can, for example, be U-shaped. The housings 26 then form a quick mechanical attachment of the second honeycomb structure 16 to the first honeycomb structure 2. The second honeycomb structure 16 can also be glued or welded to the first honeycomb structure 2 depending on the material used for the second honeycomb structure. For example, the second honeycomb structure will advantageously be glued to the first honeycomb structure if it contains paper.

[0088] Alternatively, the vertices 80 of the peripheral walls 8 of the first honeycomb structure 2 may have recesses 800, for example grooves, channels or narrow slots, into which the base 240 of the peripheral walls 24 of the second honeycomb structure 16 may be inserted. An example of such a configuration is illustrated in Figures 8 and 9.

[0089] The acoustic panel 1 can be, for example, a two-degree-of-freedom or DDOF panel (“double degree of freedom”) (Figures 1 to 9).

[0090] The acoustic attenuation panel 1 may for example include an acoustically permeable membrane 18.

[0091] For example, the acoustically permeable membrane 18 can extend parallel to the plurality of ribs 10 and / or the porous layer 12.

[0092] For example, the acoustically permeable membrane 18 may include the same characteristics as the peripheral walls 24 of the second alveolar structure 16. For example, the acoustically permeable membrane 18 and the peripheral walls 24 of the second alveolar structure 16 may each have the thickness and density characteristics previously described.

[0093] For example, the acoustically permeable membrane 18 and the peripheral walls 24 of the second alveolar structure 16 may each have a thickness less than or equal to 1 mm, for example between 0.05 and 1 mm, for example between 0.1 and 0.5 mm, and a density less than or equal to 100 kg / m3, preferably less than or equal to 60 kg / m3, even more preferably less than or equal to 40 kg / m3

[0094] Advantageously, the acoustically permeable membrane 18 and the peripheral walls 24 have a thickness between 0.05 and 0.8 mm, for example between 0.1 and 0.5 mm.

[0095] Alternatively, the acoustically permeable membrane 18 and the peripheral walls 24 of the second alveolar structure 16 may each have a density less than or equal to 100 kg / m3, for example less than or equal to 60 kg / m3, for example less than or equal to 40 kg / m3.

[0096] Alternatively, the acoustically permeable membrane 18 and the peripheral walls 24 of the second alveolar structure 16 may each have a thickness less than or equal to 1 mm, for example between 0.05 mm and 1 mm, for example less than 0.5 mm.

[0097] For example, the density of the walls and the membrane may be less than 3, for example less than 2.

[0098] For example, the acoustically permeable membrane 18 and the peripheral walls 24 of the second alveolar structure 16 can be formed by a film, for example, a thin film. The film can be a film of a material comprising, for example, a thermoplastic polymer, for example, based on poly(ethylene terephthalate) (PET), polyamides (PA), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyetherimide (PEI), polyetheretherketone (PEEK), or a thermosetting material, for example, epoxy. Phenolic resin, or polyimide. The material can, for example, be filled with short fibers of glass, carbon, aramid, basalt, or ceramic (preferably at volumetric levels between 15% and 40%). The film can, for example, be in the form of a thin layer with a thickness between 0.05 mm and 1 mm.

[0099] For example, the acoustically permeable membrane 18 and the peripheral walls 24 of the second honeycomb structure 16 can be made of a paper material, for example, include a paper material, for example, are made of paper. By paper is meant a fibrous texture of discontinuous fibers arranged in a plane and forming a thin layer. The paper can be a paper made of cellulosic fibers, mineral fibers (including, for example, glass fibers), or organic fibers (including, for example, aramid fibers or carbon fibers). Thus, it can be a material in the form of strips or sheets with a surface mass between 50 g / m² and 300 g / m². For example, the paper can be coated with one or more layers of baked thermosetting resin or thermoplastic polymer, for example, in order to increase the stiffness of the membrane and the walls.

[0100] In another example, the acoustically permeable membrane 18 and the peripheral walls 24 of the second alveolar structure 16 can be formed from thin aluminum strip.

[0101] In a first variant illustrated in figures 1 to 7, the acoustic membrane 18 can be arranged between the first and second alveolar structure 2, 16, for example at the base 240 of the peripheral walls 24 of the second alveolar structure 16.

[0102] In this variant, the second alveolar structure 16 may include the acoustic membrane 18.

[0103] In a variant illustrated in [Fig. 8], part or all of the acoustic membrane 18 can extend into the cavity of the acoustic cells 20 of the second honeycomb structure 16, for example, between the base 240 and the apex 246 of the peripheral walls 24 of the second honeycomb structure 16. This configuration can reduce the height of the walls 8 of the first honeycomb structure while keeping the acoustically permeable membrane 18 away from the porous layer 12, thus obtaining a lighter acoustic panel. The second honeycomb structure 16 can include the acoustic membrane 18.

[0104] In another variant illustrated in [Fig. 9], part or all of the acoustic membrane 18 may extend into the cavity 6 of the acoustic cells 4 of the first alveolar structure 2, for example between a base 82 and the apex 80 of the peripheral walls 8 of the first alveolar structure 2. The permeable membrane Acoustically, it can be fixed, for example by gluing, to the peripheral walls of the first alveolar structure.

[0105] In the example illustrated in Figures 1, 2, 8 and 9, the first alveolar structure 2 and the second alveolar structure 16 have the same number of peripheral walls. The first alveolar structure 2 comprises the same number of acoustic cells as the second alveolar structure 16. In this example, each peripheral wall 24 of the second alveolar structure 16 is designed to be adjacent to one of the peripheral walls 8 of the first alveolar structure 2, for example, to extend in the geometric continuity of one of the peripheral walls 8 of the first alveolar structure 2.

[0106] Figures 3, 4, 5, 6 and 7 illustrate further embodiments of the acoustic attenuation panel 1 in which the second honeycomb structure 16 comprises more peripheral walls than the first honeycomb structure 2. For example, the second honeycomb structure 16 may include first peripheral walls 242, for example, present in the same number as the peripheral walls of the first honeycomb structure 2, and additional peripheral walls 244. This configuration makes it possible to provide slightly more stiffness to the second honeycomb structure 16 and in particular to the acoustic membrane 18.

[0107] The number of additional peripheral walls 244 of the second alveolar structure 16 can be modulated for each cell 6 of the first alveolar structure 2, the number of additional peripheral walls being between 0 and N (N being less than 25, preferably less than 10), to obtain a greater or lesser degree of partitioning of the cells 20 of the second structure corresponding to each cell 6 of the first structure. For example, a distance between two walls can be a minimum of 4 mm and a maximum of 70 mm.

[0108] In a first variant illustrated in Figures 3 and 4, the first peripheral walls 242 and the additional peripheral walls 244 of the second alveolar structure can, for example, all extend from one face, for example the same face, for example a first face 180 of the acoustically permeable membrane 18. The cavities 22 of the acoustic cells 20 of the second alveolar structure 16, for example formed by these peripheral walls 242, 244, have a diameter smaller than the diameter of the cavities 6 of the acoustic cells 8 of the first alveolar structure 2. The second alveolar structure forms series of cavities extending in two directions, for example coplanar.

[0109] In the example shown in [Fig. 5], among the peripheral walls 24 of the second alveolar structure 16, some peripheral walls 242 may extend from a first face 180 of the acoustically permeable membrane 18 and other peripheral walls 244, for example the peripheral walls Additional 244 may extend from a second face 182 of the acoustically permeable membrane 18, for example opposite the first face 180 of the acoustically permeable membrane 18. In one example, the peripheral walls 242 extending from the first face 180 of the permeable membrane 18 may have housings 26, for example in the shape of a U. For example, the peripheral walls 244 extending from the second face 182 of the permeable membrane 18 extend into some of the acoustic cells 4 of the first alveolar structure 2. Thus, some acoustic cells 20 of the second alveolar structure 16 extend into the cavity 6 of some acoustic cells 4 of the first alveolar structure.

[0110] The cavity of the acoustic cells 20 of the second alveolar structure extending from the first face 180 of the acoustically permeable membrane 18 can have a diameter equivalent to that of the acoustic cells 4 of the first alveolar structure 2.

[0111] The cavity of the acoustic cells 20 of the second alveolar structure 16 which extend into the cavity 6 of certain acoustic cells 4 of the first alveolar structure 2 have a diameter smaller than that of the acoustic cells of the first alveolar structure.

[0112] This configuration reduces the diameter of the acoustic cell cavities in the first alveolar structure. This configuration is advantageous for shorter wavelengths (higher frequencies). This configuration can be achieved by folding certain portions of the material intended to form the peripheral walls in opposite directions (downward and upward), as shown in [Fig. 6]. Furthermore, this configuration avoids increasing the number of cells 4 in the first alveolar structure 2, thus preventing it from becoming too heavy.

[0113] In a variant illustrated in [Fig.7], among the additional peripheral walls 244 of the second honeycomb structure 16, some of the additional walls 244 may extend from a first face 180 of the acoustically permeable membrane and other walls, for example the other walls, may extend from the second face 182 of the acoustically permeable membrane 18, for example opposite to the first face 180 of the acoustically permeable membrane 18. The advantage of this positioning is that, for reasons of structural strength, the height of the partitions 8 of the first structure may be greater than the distance required between 12 and 18 to meet the acoustic requirement.

[0114] The configurations with the additional acoustic walls illustrated in Figures 3, 4, 5 and 7 can be achieved, whether the membrane 18 is part of the second alveolar structure 16 (Figures 3 to 5), for example by folding ([Fig. 6]) or whether the membrane 18 is fixed, for example by gluing to the walls of the first alveolar structure 2. In the embodiment illustrated in [Fig.9] for example, and according to an alternative embodiment the acoustic attenuation panel may include additional peripheral walls extending on one side and / or the other side of the acoustically permeable membrane 18.

[0115] As illustrated in [Fig.6], the acoustically permeable membrane 18 and at least some of the peripheral walls 24 of the second alveolar structure 16 can be formed by folding and, for example, gluing the material, for example, of the same material, for example, so that the peripheral walls 24 extend transversely, for example, orthogonally, with respect to the acoustically permeable membrane 18.

[0116] For example, the acoustically permeable membrane 18 and the peripheral walls 24 of the second honeycomb structure 16 can be formed from the same material, for example, paper or film. The material can include, for example, micro-perforated portions forming the acoustically permeable membrane 18 and folded portions forming the peripheral walls 24.

[0117] The peripheral walls 24 can be obtained by casting or injecting material into a mold, by deforming material (for example by thermoforming or thermoflow), or by folding and gluing, for example.

[0118] In the illustrated examples, each acoustic cell 4, 20 of the first alveolar structure 2 and the second alveolar structure 16 may have a polygonal cross-section, for example a square cross-section. In this example, each acoustic cell comprises a cavity delimited by four peripheral walls.

[0119] The shape of these acoustic cells is not limited to that previously described. For example, the cross-section of each cell can be rectangular, triangular, hexagonal, etc. The acoustic cells 4, 20 can have cross-sections of different shapes.

[0120] In the examples just described with reference to Figures 1 to 9, the peripheral walls 24 of the second honeycomb structure 16 may have different heights. Height is understood to be the distance measured between the base 240 and the apex 246 of each of the walls 24. For example, some of the walls of the second honeycomb structure 16 may have a different height from the other walls of the second honeycomb structure 16. For example, the additional walls 244 of the second honeycomb structure 16 may have a different height from the height of the first walls 242 of the second honeycomb structure 16. For example, the height of the additional walls 244 is less than the height of the first walls 242 of the second honeycomb structure 16. The additional wall height 244 is equivalent to, for example, a maximum of 30% of the height of the first walls 242 of the second honeycomb structure. This allows for a further reduction in the weight of the second honeycomb structure and / or the development of larger acoustic cavity behaviors 22.

[0121] As illustrated in [Fig. 10], the acoustic panel 1 can, for example, be a single-degree-of-freedom (SDOF) panel. The acoustic panel 1 can be devoid of the acoustically permeable membrane 18.

[0122] The acoustic panel 1 may include the first honeycomb structure 2 comprising the peripheral walls 8 and the plurality of acoustic cells 4, each acoustic cell 4 comprising a cavity 6 delimited by several of the peripheral walls 8, and the second honeycomb structure 16 comprising the peripheral walls 24 and a plurality of acoustic cells 20, each acoustic cell 20 comprising a cavity 22 delimited by several of the peripheral walls 24, in which the peripheral walls 24 of the second honeycomb structure 16 have the thickness and density characteristics as previously described.

[0123] The peripheral walls 24 of the second alveolar structure 16 may have the housing 26 provided in a base 240 of these walls and complementary to a vertex 80 of the peripheral walls 8 of the first alveolar structure so as to allow a fitting of the second alveolar structure 16 on the first alveolar structure 2.

[0124] The acoustic panel 1, for example the second honeycomb structure 16, may include more peripheral walls than the first honeycomb structure 2. For example, the second honeycomb structure 16 may include first peripheral walls 242, for example, present in the same number as the peripheral walls of the first honeycomb structure 2, and additional peripheral walls 244. This configuration makes it possible to provide a little more stiffness to the second honeycomb structure 16.

[0125] The peripheral walls, 24, for example the additional peripheral walls 244, can form heterogeneous geometric patterns. For example, the peripheral walls 24, for example the additional peripheral walls 244, can be arranged so as to form acoustic cells in the shape of a quadrilateral and / or a triangle, for example.

[0126] The peripheral walls 24 of the second honeycomb structure 16 may have different heights. Height is defined as the distance measured between the base 240 and the apex 246 of each of the walls 24. For example, some of the walls of the second honeycomb structure 16 may have a different height than the other walls of the second honeycomb structure 16. For example, the additional walls 244 of the second honeycomb structure 16 may have a The height of the additional walls 244 differs from the height of the first walls 242 of the second alveolar structure 16. For example, the height of the additional walls 244 is less than the height of the first walls 242 of the second alveolar structure 16. For example, the height of the additional walls 244 is equal to 30%, for example, a maximum of 30%, of the height of the first walls 242 of the second alveolar structure. This allows the second alveolar structure to be further lightened and / or to exhibit more pronounced acoustic cavity behavior 22. For example, the height of the additional walls 244 is greater than the height of the first walls 242 of the second alveolar structure 16. The peripheral walls 24, for example, the additional peripheral walls 244, may have different heights.

[0127] In the examples shown, acoustic cells may include peripheral walls in common with adjacent acoustic cells.

[0128] The acoustic attenuation panel 1 as described in the previous examples can be attached and fixed to a turbomachine, for example inside a blower casing and / or inside an outer shell of the intermediate casing and / or attached and fixed inside a nacelle.

[0129] For example, the acoustic attenuation panel 1 may include fixing arms 28. In the figures, only one fixing arm is visible. Each fixing arm 28 may extend from a portion of a peripheral wall 8 of the first honeycomb structure 2 and may be formed as a single piece with the first honeycomb structure. Each fixing arm 28 may have a height corresponding to the height of the second honeycomb structure 16.

[0130] Figure 11 illustrates a propulsion assembly 5 extending along a longitudinal axis X, comprising a nacelle 50 and a turbomachine 500. The turbomachine 500 may include a fan 510 and a housing, for example a fan housing, surrounding the fan. The turbomachine 500 may include a sound attenuation panel 1 as previously described, arranged, for example, on a housing of the turbomachine. The nacelle 50 has a structure comprising an upstream section forming an air inlet 52, a middle section 54 comprising fan cowls intended to surround a fan 510 of the turbomachine 500, a downstream section 56 comprising a thrust reverser and intended to surround the combustion chamber of the turbomachine and an ejection nozzle 58. The nacelle may include an acoustic attenuation panel 1 as previously described.

[0131] For example, the air inlet 52 includes an inner face 53 oriented towards the blower 510, said inner face can receive at least one acoustic attenuation panel 1 according to the examples just described.

[0132] As illustrated in [Fig.1 1], other components of the nacelle such as the thrust reverser for example, can receive the acoustic attenuation panel 1 according to the examples just described.

Claims

Demands

1. Acoustic attenuation panel (1) comprising: - a first honeycomb structure (2) comprising peripheral walls (8) and a plurality of acoustic cells (4), each acoustic cell (4) comprising a cavity (6) delimited by several of the peripheral walls (8), - a second honeycomb structure (16) comprising peripheral walls (24) and a plurality of acoustic cells (20), each acoustic cell (20) comprising a cavity (22) delimited by several of the peripheral walls (24), in which the peripheral walls (24) of the second honeycomb structure (16) each have a thickness less than or equal to 1 mm and a density less than or equal to 100 kg / m3.

2. Acoustic attenuation panel (1) according to claim 1 in which the peripheral walls (24) of the second honeycomb structure (16) are made of thermoplastic film.

3. Acoustic attenuation panel (1) according to any one of claims 1 wherein the peripheral walls (24) of the second honeycomb structure (16) are made of paper.

4. Acoustic attenuation panel (1) according to any one of the preceding claims wherein at least some of the peripheral walls (24) of the second honeycomb structure (16) have a housing (26) formed in a base (240) of these walls and complementary to a top (80) of the peripheral walls (8) of the first honeycomb structure (2) so as to allow the second honeycomb structure (16) to be fitted onto the first honeycomb structure (2) and / or wherein at least some of the peripheral walls (8) of the first honeycomb structure (2) have a housing (800) formed in a top (80) of these walls and complementary to a base (240) of the peripheral walls (24) of the second honeycomb structure (16) so as to allow the second honeycomb structure (16) to be fitted onto the first honeycomb structure (2).

5. Acoustic attenuation panel (1) according to any one of the preceding claims, wherein at least some of the walls (24) of the second alveolar structure (16) have different heights from each other.

6. Acoustic attenuation panel (1) according to any one of the preceding claims wherein the second honeycomb structure (16) comprises more peripheral walls than the first honeycomb structure (2).

7. Acoustic attenuation panel (1) according to any one of the preceding claims wherein the acoustic attenuation panel (1) comprises an acoustically permeable membrane (18), the acoustically permeable membrane (18) and the peripheral walls (24) of the second honeycomb structure (16) each have a thickness less than or equal to 1 mm and a density less than or equal to 100 kg / m3.

8. Acoustic attenuation panel (1) according to the preceding claim in combination with claim 7 wherein certain peripheral walls (242) of the second honeycomb structure extend from a first face (180) of the acoustically permeable membrane (18) and other peripheral walls (244) of the second honeycomb structure (16) extend from a second face (182) of the acoustically permeable membrane (18) such that certain acoustic cells (20) of the second honeycomb structure (16) extend into the cavity (6) of certain acoustic cells (4) of the first honeycomb structure (2).

9. Acoustic attenuation panel (1) according to any one of claims 7 or 8 wherein the acoustically permeable membrane (18) is made of thermoplastic film or paper.

10. Acoustic attenuation panel (1) according to any one of claims 7 to 9 wherein the acoustically permeable membrane (18) and at least some of the peripheral walls (24) of the second honeycomb structure (16) are formed by folding a material so that said peripheral walls (24) extend transversely with respect to the acoustically permeable membrane (18).

11. Acoustic attenuation panel (1) according to any one of claims 7 to 10 wherein the acoustically permeable membrane (18) extends into the cavity of the acoustic cells (4) of the first alveolar structure (2).

12. Acoustic attenuation panel (1) according to any one of claims 7 to 10 wherein the acoustically permeable membrane (18) extends into the cavity of the acoustic cells (20) of the second alveolar structure (16).

13. Aircraft turbomachine (500) comprising a sound attenuation panel (1) according to any one of the preceding claims.

14. Aircraft nacelle (50) comprising a sound attenuation panel (1) according to any one of claims 1 to 12.