Cellular structure for an acoustic panel

Abstract

The invention relates to a cellular structure for an acoustic panel, the cellular structure comprising: - at least one acoustic cell comprising a cavity bounded by a peripheral wall; and - at least one first partition (24) arranged in the cavity to divide the cavity into two, the first partition (24) comprising a first acoustically permeable membrane (25), characterised in that the first partition (24) further comprises first lugs (26), each first lug (26) being received in a respective first slot formed in the peripheral wall to mechanically fasten the first partition (24) in the corresponding cavity.

Description

[0001] DESCRIPTION

[0002] TITLE: HONEYCOMB STRUCTURE FOR AN ACOUSTIC PANEL

[0003] Technical field of the invention

[0004] The invention relates to the field of honeycomb structures for acoustic panels of aircraft turbomachines.

[0005] Technical background

[0006] An aircraft turbomachine typically has a longitudinal axis. It comprises, 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.

[0007] The blower allows the suction of an air flow divided into a primary flow and a secondary flow. The primary flow passes through a primary vein of the turbomachine while the secondary flow is directed towards a secondary vein surrounding the primary vein.

[0008] The primary flow is compressed within the compressors. The compressed air is then mixed with fuel and burned within the combustion chamber. The gases from the combustion pass through the turbines and then escape through the nozzle, whose cross-section allows the acceleration of these gases to generate propulsion.

[0009] The fan typically comprises a movable disc rotating about the longitudinal axis and blades mounted on the disc. The blades are surrounded by a fan casing centered on the longitudinal axis and intended to retain the blades in the event of damage, for example, to the blades.

[0010] The fan casing is typically surrounded by a nacelle that protects the fan. Such a fan is called a shrouded fan, as opposed to unshrouded fans, whose blades are not surrounded by a shroud.

[0011] The turbomachine further comprises an intermediate casing located downstream of the fan casing and defining a portion of the secondary vein v2.

[0012] Turbomachinery is a significant source of noise pollution, and there is a strong demand to reduce this type of pollution. Also, given the revolution in the configuration of turbomachinery, the rotation speed of the fans tends to decrease. However, the slower the rotation speed, the lower the frequencies of the generated sound waves. Moreover, the sound waves generated by turbomachinery can extend over a wide frequency range.

[0013] To this end, it has been proposed to equip certain components of the turbomachine such as the fan and intermediate casings and / or the nacelle with acoustic panels in order to reduce the noise generated by the turbomachines.

[0014] An acoustic panel typically comprises a honeycomb structure comprising acoustic cells forming Helmholtz resonators. The acoustic cells each comprise a peripheral wall extending from an inner edge to an outer edge in a first direction parallel to the propagation of the sound waves in each acoustic cell. Each acoustic cell further comprises a cavity delimited by the peripheral wall and in which these sound waves propagate.

[0015] The number of honeycomb structures in the acoustic panel determines the acoustic performance of the acoustic panel with respect 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. Acoustic panels with double honeycomb structures or triple honeycomb structures have thus been proposed. Typically, an acoustic panel with a double honeycomb structure, also known by the English acronym DDOF for "Double Degree of Freedom" as opposed to an acoustic panel with a single honeycomb structure, also known by the English acronym SDOF for "Single Degree of Freedom", comprises first and second honeycomb structures separated by a membrane permeable to sound waves.Each honeycomb structure is therefore capable of attenuating sound waves over a given and distinct frequency range. Such a configuration of the acoustic panel with double or triple honeycomb structures makes it possible to expand the frequency range of attenuated sound waves.

[0016] However, compared to acoustic panels with a simple honeycomb structure, these panels have a greater thickness due to the superposition of the honeycomb structures.

[0017] Furthermore, the height of the acoustic cells as measured along the first direction determines the frequency at which the acoustic attenuation of the acoustic cells is maximum. Typically, a honeycomb structure with a thickness of 30 millimeters is suitable for attenuating frequencies close to 2000 Hz, and a honeycomb structure with a thickness of 70 millimeters is suitable for attenuating frequencies close to 880 Hz. Thus, to absorb low-frequency sound waves, the acoustic panels must be of significant thickness given the height of the acoustic cells. Such a thickness is not suitable for the size of turbomachines.

[0018] In this context, document FR-A1-3070530 proposes arranging at least one partition in a cavity of an acoustic cell to separate the cavity according to the direction of propagation of the sound waves. According to this document, the partition makes it possible to create a baffle to increase the distance traveled by a sound wave. The greater this distance, the lower the frequency range of the attenuated sound waves. Thus, for the same acoustic cell height, the acoustic panel integrating a partition in the cavities can attenuate sound waves over a lower frequency range.

[0019] Also, this document proposes adding a septum in order to increase the frequency range of attenuated sound waves.

[0020] Despite the advantages this solution offers in terms of acoustic performance, such a solution presents major challenges related to the integration of such a partition into the cavity of the acoustic cells. Indeed, according to document FR-A1 -3070530, the integration of such partitions requires welding, soldering or even bonding operations which are long, tedious and particularly costly.

[0021] In this context, there is a need to provide an acoustic panel with a low thickness and capable of absorbing sound waves over a wide frequency range while being simple, quick to manufacture and inexpensive.

[0022] Summary of the invention

[0023] To this end, the invention proposes a honeycomb structure for an acoustic panel of an aircraft turbomachine, the honeycomb structure comprising

[0024] - at least one acoustic cell comprising a cavity and a peripheral wall delimiting the cavity, the peripheral wall extending in a first direction, and

[0025] - at least one first partition arranged in the cavity to separate the cavity in two along the first direction, the first partition comprising a first acoustically permeable membrane and extending transversely to the first direction.

[0026] The alveolar structure is remarkable in that the first partition further comprises first lugs, each first lug being received in a respective first slot provided in the peripheral wall to mechanically fix the first partition in the corresponding cavity, the first membrane having a polygonal shape having peripheral edges connected by vertices and the first lugs extending respectively in the first direction from the vertices of the first membrane.

[0027] The honeycomb structure according to the invention comprises at least a first partition arranged in the cavity of the acoustic cell. Such a partition makes it possible to improve the acoustic attenuation performance of the acoustic panel in terms of frequency range and / or level without increasing the height of the honeycomb structure.

[0028] According to the invention, this first partition is mechanically fixed to the acoustic cell. Indeed, the slot system provided on the peripheral wall of the acoustic cell receiving the partition and the lug provided on the first partition constitutes a mechanical attachment facilitating the integration of such a first partition.

[0029] Such mechanical anchoring eliminates the need for tedious and costly welding, soldering or gluing of partitions.

[0030] The manufacture of the honeycomb structure is thus simple and quick to manufacture and therefore inexpensive.

[0031] The invention may comprise one or more of the following features, taken in isolation from each other or in combination with each other:

[0032] - the first membrane has a flat shape complementary to a cross-section of the cavity,

[0033] - the first membrane has a hexagonal, square or rectangular shape,

[0034] - the first membrane comprises a first skin surrounded by the peripheral edges, the first skin being a lattice or having holes,

[0035] - the first membrane comprises a first acoustically impermeable skin and at least one peripheral opening, - the first partitions fit into each other to connect the first partitions together,

[0036] - a second partition arranged in the cavity, the first and second partitions being offset in the first direction to separate the cavity into three, the second partition comprising a second acoustically permeable membrane extending transversely to the first direction and second lugs received respectively in a second slot provided on the peripheral wall to mechanically fix the second partition in the corresponding cavity,

[0037] - the first and second membranes respectively comprise first and second transversely opposed peripheral openings to allow propagation of sound waves in the cavity by a baffle effect,

[0038] - a third partition arranged in the cavity, the first, second and third partitions being offset in the first direction to separate the cavity into four, the third partition comprising a third acoustically permeable membrane extending transversely to the first direction and third lugs received in respective third slots to mechanically fix the third partition in the corresponding cavity,

[0039] - the third membrane comprises a mesh or a perforated layer.

[0040] The invention also relates to an acoustic panel for an aircraft turbomachine comprising:

[0041] - a porous layer,

[0042] - a perforated layer, and

[0043] - a honeycomb structure according to any one of the preceding characteristics, the perforated structure being arranged in a sandwich between the porous layer and the honeycomb structure. Brief description of the figures

[0044] Other characteristics and advantages will emerge from the following description of non-limiting embodiments of the invention with reference to the appended drawings in which: Figure 1 is a schematic representation in longitudinal section of a half-turbomachine of an aircraft, Figure 2 is a perspective representation of an acoustic panel according to the invention, Figure 3 is a perspective representation of an acoustic cell according to an exemplary embodiment of the invention, Figure 4 is a perspective representation of an acoustic cell according to another exemplary embodiment of the invention, Figure 5 is a schematic representation of a first partition according to an exemplary embodiment of the invention, Figure 6 is a schematic representation of a first partition according to another exemplary embodiment of the invention, Figure 6a is a schematic representation of a first partition according to another exemplary embodiment of the invention,Figure 7 is a perspective representation of a honeycomb structure according to an exemplary embodiment of the invention, Figure 8 is a longitudinal sectional representation of a peripheral wall of the honeycomb structure of Figure 7, Figure 9 is a schematic representation of first partitions equipping the honeycomb structure of Figure 7, Figure 10 is a perspective representation of an acoustic cell in which first and second partitions are arranged according to another exemplary embodiment of the invention, Figure 11 is a sectional representation of the acoustic cell of Figure 10, Figure 12 is a perspective representation of one of the partitions equipping the acoustic cell of Figure 10, Figure 13 is a sectional representation of one of the partitions of Figure 10, Figure 14 is a sectional representation of an acoustic cell in which first,second and third partitions according to another exemplary embodiment of the invention, figure 15 is a sectional representation of a honeycomb structure according to another embodiment of the invention.,

[0045] Detailed description of the invention

[0046] An example of a turbomachine 1 for an aircraft is shown in Figure 1. The turbomachine 1 extends around and along a longitudinal axis A.

[0047] In the present application, the terms “upstream” and “downstream” are defined in relation to the direction of circulation of the gases in the turbomachine 1 along the longitudinal axis A.

[0048] The terms "axial", "axially", "radial", "radially" are defined in relation to the longitudinal axis A.

[0049] The terms "internal", "interior", "internally", "external", "externally", "externally", are defined with respect to the distance from the longitudinal axis A along an axis Z perpendicular to the longitudinal axis A. The turbomachine 1 is preferably a turbojet, for example a twin-spool, twin-flow turbojet. It comprises, from upstream to downstream, a fan 2, at least one compressor such as a low-pressure compressor 3 and a high-pressure compressor 4, a combustion chamber 5, at least one turbine such as a high-pressure turbine 6 and a low-pressure turbine 7, and a gas exhaust nozzle.

[0050] The low and high pressure compressors 3, 4 and the high and low pressure turbines 6, 7 each comprise at least one rotor. The rotor of the low pressure compressor 3 is connected to the rotor of the low pressure turbine 7 by a low pressure shaft 8 and the rotor of the high pressure compressor 4 is connected to the rotor of the high pressure turbine 6 by a high pressure shaft 9. The high pressure shaft 9 is arranged coaxially around the low pressure shaft 8. The low pressure and high pressure shafts 8, 9 are centered on the longitudinal axis A.

[0051] The fan 2 comprises a disk movable in rotation about the longitudinal axis A and blades 10 extending radially from the disk. The fan 2 further comprises a fan shaft (not shown) connected to the low pressure shaft 8 via a speed reducer for example.

[0052] The blower 2 allows the suction of an air flow F dividing into a primary air flow F1 and a secondary air flow F2. The primary air flow F1 passes through a primary vein v1 of the turbomachine 1 and the secondary flow F2 flows into a secondary vein v2 of the turbomachine 1. The secondary vein v2 surrounds the primary vein v1.

[0053] The primary flow F1 is compressed within the low pressure compressor 3 then the high pressure compressor 4. The compressed air is then mixed with a fuel and burned within the combustion chamber 5. The gases formed by the combustion pass through the high pressure and low pressure turbines 6, 7. The gases finally escape through the nozzle, the section of which allows the acceleration of these gases to generate propulsion.

[0054] The fan 2 is of the shrouded type. The turbomachine 1 thus further comprises a fan casing 11. The fan casing 11 is annular and centered on the longitudinal axis A. It is arranged around the blades 10. The fan casing 11 forms a portion of the secondary vein v2.

[0055] The turbomachine 1 further comprises an intermediate casing 12. The intermediate casing 12 is arranged downstream of the fan casing 11. 11 is connected to the fan casing 11, for example, by flanges.

[0056] The intermediate casing 12 is centered on the longitudinal axis A and comprises an inner shell 13 and an outer shell 14 connected by arms 15. The outer shell 14 is annular and centered on the longitudinal axis A. It is arranged coaxially around the inner shell 13. The outer shell 14 delimits with the inner shell 13 a portion of the secondary vein v2. The turbomachine 1 further comprises a nacelle 16. The nacelle 16 is arranged around the fan and intermediate casings 11, 12.

[0057] In order to reduce the noise pollution generated by the turbomachine 1, the turbomachine 1 comprises at least one and advantageously acoustic panels 17. Each acoustic panel 17 according to the invention is advantageously capable of absorbing acoustic energy over a frequency range between 100 Hz and 1500 Hz.

[0058] Each acoustic panel 17 extends over an angular sector or has an annular shape centered on the longitudinal axis A. Each acoustic panel 17 can be attached and fixed inside the fan casing 11 and / or inside the external shroud 14 of the intermediate casing 12 and / or inside the nacelle 16.

[0059] With reference to Figure 2, each acoustic panel 17 advantageously has a sandwich structure. Each acoustic panel 17 comprises a honeycomb structure 18 and advantageously a perforated layer 19 and a porous layer 20. The perforated layer 19 is located between the honeycomb structure 18 and the porous layer 20.

[0060] When the acoustic panel 17 is mounted in the turbomachine 1, the honeycomb structure 18 is located radially on the outside while the porous layer 20 is located radially on the inside, the perforated acoustic structure 19 being located radially between the honeycomb and porous layers 18, 20.

[0061] Advantageously, the acoustic panel 17 has a thickness e1 in a first direction Y parallel to the propagation of the sound waves in the acoustic panel 17 of between 10 mm and 100 mm, in particular between 20 mm and 50 mm.

[0062] Advantageously, the cellular structure 18 has a height h1 as measured along the first direction Y of between 10 mm and 100 mm, in particular between 10 mm and 60 mm. The cellular structure 18 comprises, for example, a metallic material such as aluminum, in particular an aluminum alloy chosen from the 6000 series or a polymeric material chosen, for example, from thermoplastics or composites.

[0063] The honeycomb structure 18 comprises at least one acoustic cell 21 and advantageously a plurality of acoustic cells 21. The acoustic cells 21 form Helmholtz resonators. The acoustic cells 21 are joined to form a honeycomb structure. Each acoustic cell 21 comprises a peripheral wall 22 and a cavity 21a delimited by the peripheral wall 22.

[0064] The peripheral walls 22 extend in the first direction Y over the entire height of the cellular structure 18. The peripheral walls 22 extend from the perforated layer 19 between an inner edge 22a and an outer edge 22b opposite the perforated layer 19. Thus, the peripheral walls 22 extend in the first direction Y from the perforated layer 19. Advantageously, the outer edge 22b of at least one acoustic cell 21 has threads (not shown) for fixing the acoustic panel 17 in the turbomachine 1. Each peripheral wall 22 has lateral faces 22c connected to each other by edges 22d which extend between the inner edge 22a and the outer edge 22b.

[0065] Indeed, each acoustic cell 21 has a polygonal cross-section. The cross-section of each acoustic cell 21 is for example rectangular as illustrated in Figure 2, or hexagonal as illustrated in Figure 3 or even square as illustrated in Figure 4. The cross-section of the acoustic cells 21 may differ from one acoustic cell 21 to another.

[0066] According to the invention, each peripheral wall 22 further comprises at least one first slot 23.

[0067] According to a first example illustrated in Figures 3 and 4, each peripheral wall 22 comprises a plurality of slots 23 which are preferentially formed in the edges 22d of each peripheral wall 22. The slots 23 have, for example, an elongated shape along the first direction Y.

[0068] According to another example illustrated in Figures 7 and 8, each peripheral wall 22 comprises a first slot 23 formed on at least one of the lateral faces 22c. According to this example, each first slot 23 has a U shape which opens onto the internal or external edge 22a, 22b.

[0069] The cavities 21a have, for example, diameters between 8 mm and 100 mm, in particular between 10 mm and 60 mm.

[0070] According to the invention, the cellular structure 18 further comprises at least one, and advantageously a plurality of first partitions 24. Each first partition 24 is located in a respective cavity 21a and separates this cavity 21a in two along the first direction Y. As better visible in FIGS. 5 and 6, each first partition 24 comprises a first membrane 25 and first lugs 26 for connection to the peripheral wall 22 of each acoustic cell 21.

[0071] Advantageously, the first membranes 25 comprise a polymeric material chosen for example from thermoplastics or thermosets, a metallic material, a ceramic material or even a mixture of these.

[0072] Each first membrane 25 extends in a second direction X transverse to the first direction Y. Each first membrane 25 has a substantially planar shape complementary to the cross-section of the corresponding cavity 21a. Thus, the first membranes 25 have, for example, a square, hexagonal shape as illustrated in FIG. 5 or rectangular shape as illustrated in FIG. 6 or a combination thereof.

[0073] The first membranes 25 have peripheral edges 25a connected by vertices 25b. The first membranes 25 further comprise a skin 25c surrounded by the peripheral edges 25a. The peripheral edges 25a and the peripheral wall 22 of the corresponding acoustic cell 21 are contiguous.

[0074] According to the invention, each first membrane 25 is acoustically permeable. The acoustic permeability of the first membranes 25 advantageously differs from the acoustic permeability of the peripheral walls 22 in order to increase the attenuation frequency range of the sound waves of the acoustic panel 17.

[0075] According to a first example, the skin 25c is a lattice. The peripheral edges 25a are for example overmolded onto the skin 25c.

[0076] In another example, the 25c skin has holes for the passage of sound waves. The holes have, for example, a diameter of between 0.1 mm and 5 mm, in particular between 0.1 mm and 2 mm. The opening rate of the 25c skin is, for example, between 1% and 6%. The opening rate corresponds to the ratio between the open surface and the total surface of the 25c skin.

[0077] According to yet another example illustrated in Figure 6a, the skin 25c is acoustically impermeable. The skin 25c is said to be “solid”. In other words, the skin 25c is devoid of orifices. According to this embodiment, the membrane 25 further comprises a peripheral opening 25d for the passage of sound waves.

[0078] Thus, each first membrane 25 forms a septum and allows the acoustic cell 21 in which it is arranged to attenuate the sound waves over a wide frequency range, in particular two distinct frequency ranges without increasing the height h1 of the alveolar structure 18.

[0079] Each first lug 26 is received in a respective first slot 23 to mechanically fix the first partition 24 in the corresponding cavity 21 a. Such a method of anchoring the first partitions 24 makes it possible to avoid a tedious step of gluing, welding or brazing the first partitions 24 and therefore to facilitate the mounting of the first partitions 24 in the acoustic cells 21. Advantageously, the first lugs 26 extend in the first direction Y from each vertex 25 b of the membrane 25 to a free anchoring end 26 a opposite the membrane 25.

[0080] Preferably, with reference to FIG. 9, the first partitions 24 fit together. They are, for example, assembled together by recessing. Thus, the first partitions 24 have, for example, tongues 27 which fit into grooves of adjacent partitions 24. Such an embodiment makes it possible to pre-assemble the first partitions 24 before their installation in the acoustic cells 21.

[0081] According to a particularly advantageous embodiment illustrated in Figure 10, the cellular structure 18 further comprises a second partition 28 arranged in at least one cavity 21a to separate said cavity 21a into three. The first and second partitions 24, 28 are thus offset along the first direction Y. Advantageously, the cellular structure 18 comprises a plurality of second partitions 28.

[0082] Each second partition 28 comprises a second membrane 29 and second lugs 30 for connection to the peripheral wall 22 of each acoustic cell 21.

[0083] Each second membrane 29 extends along the second direction X transverse to the first direction Y. Each second membrane 29 has a planar shape complementary to the cross-section of the corresponding cavity 21a. Thus, the second membranes 29 have, for example, a rectangular, hexagonal, square shape or a combination thereof.

[0084] As can be seen in Figure 12 for example, the second membranes 29 have peripheral edges 29a connected by vertices 29b. The second membrane 29 further comprises a skin 29c surrounded by the peripheral edges 29a. The peripheral edges 29a are for example overmolded onto the skin 29c. Advantageously, the second membranes 29 comprise a polymeric material chosen for example from thermoplastics or thermosets, a metallic material, a ceramic material or even a mixture thereof.

[0085] Each second membrane 29 is acoustically permeable. The acoustic permeability of the second membranes 29 differs from the acoustic permeability of the peripheral walls 22.

[0086] As best seen in Figure 11, each second lug 30 is received in a respective second slot 30' of the peripheral wall 22 to mechanically fix the second partition 28 in the corresponding cavity 21a.

[0087] As better seen in Figure 13, advantageously, the second lugs 30 extend in the first direction Y from each vertex 29b of the second membrane 29 to a free anchoring end 30a opposite the membrane 30.

[0088] Optionally, to facilitate the assembly of the second partitions 28, the second partitions 28 fit together. They are, for example, assembled together by recessing.

[0089] According to the embodiment illustrated in Figure 10, the first and second partitions 24, 28 respectively comprise first and second transversely opposite peripheral openings 31, 32. The first and second openings 31, 32 are located between the peripheral edge 25a, 29a, and the skin 25c, 29c.

[0090] According to this embodiment, the skin 25c, 29c of the first and second membranes 25, 29 are solid, that is to say they limit or even prevent the propagation of the sound waves. The sound waves pass through the first and second partitions 24, 28 through the first and second peripheral openings 31, 32.

[0091] Thanks to the first and second transversely opposed peripheral openings 31, 32, the sound waves propagate in the cavity 21a by a baffle effect, in other words according to a trajectory T in S. Thus, for the same height of cavity 21a, the distance traveled by the sound waves is greater according to this embodiment. The greater the distance traveled in the cavity 21a, the lower the frequency of the absorbed sound waves. Such an embodiment therefore makes it possible to absorb sound waves at a lower frequency, typically less than 1000 Hz without increasing the height of the acoustic cells 21.

[0092] According to a particularly advantageous embodiment illustrated in Figure 14, the cellular structure 18 further comprises at least one third partition 33 arranged in a cavity 21a comprising the first and second partitions 24, 28 to separate said cavity 21a into four. The first, second and third partitions 24, 28, 33 are thus offset along the first direction Y. Advantageously, the cellular structure 18 comprises a plurality of third partitions 28.

[0093] Each third partition 33 comprises a third membrane 34 and third lugs 35 for connection to the peripheral wall 22 of each acoustic cell 21.

[0094] Each third membrane 34 extends along the second direction X. Each third membrane 34 has a planar shape complementary to the cross-section of the corresponding cavity 21a. Thus, the third membranes 34 have, for example, a rectangular, hexagonal, square shape or a combination thereof. The third membranes 34 have peripheral edges connected by vertices. The third membrane 34 further comprises a skin 34c surrounded by the peripheral edges. The peripheral edges are, for example, overmolded onto the skin 34c.

[0095] Advantageously, the third membranes 34 comprise a polymeric material chosen for example from thermoplastics or thermosets, a metallic material, a ceramic material or a mixture thereof. Each third membrane 34 is acoustically permeable. The acoustic permeability of the third membranes 34 differs from the acoustic permeability of the peripheral walls 22.

[0096] Each third lug 35 is received in a respective third slot 36 of the peripheral wall 22 to mechanically fix the third partition 33 in the corresponding cavity 21a.

[0097] Advantageously, the third lugs 35 extend in the first direction Y from each vertex of the third membrane 34 to a free anchoring end opposite the membrane 34.

[0098] Optionally, to facilitate the assembly of the third partitions 33, the third partitions 33 fit together. They are, for example, assembled together by recessing.

[0099] According to the embodiment illustrated in Figure 14, the first and second partitions 24, 28 respectively comprise the first and second peripheral openings 31, 32 transversely opposed and the skin 34c of the third membrane 34 is acoustically permeable. It comprises a lattice or holes for the passage of sound waves.

[0100] Thanks to the first and second transversely opposed peripheral openings 31, 32, the sound waves propagate in the cavity 21a by a baffle effect, in other words according to an S-shaped trajectory. Thus, for the same height of cavity 21a, the distance traveled by the sound waves is longer according to this embodiment, thus allowing the absorption of lower frequency sound waves without increasing the height of the acoustic cells 21. In combination with this baffle effect allowing the attenuation of low frequency sound waves, the third partition 33 makes it possible to increase the frequency range of the absorbed sound waves.

[0101] The perforated layer 19 is located between the porous layer 20 and the cellular structure 18. The perforated layer 19 comprises perforations 19a. Preferably, the perforations 19a are regularly distributed in the perforated acoustic structure 19. The perforations 19a communicate with the cavities 21a of the acoustic cells 21. Preferably, a group of four perforations 19a communicates with a cavity 21a of an acoustic cell 21. The perforations 19a have, for example, a substantially polygonal cross-section, for example square and / or rectangular and / or circular. The perforations 19a have a dimension, for example, greater than or equal to 1 mm, in particular greater than or equal to 2 mm.

[0102] Advantageously, the perforated layer 19 has a thickness less than the thickness of the cellular structure 18. The thickness of the perforated layer 19 is between 0.5 mm and 2 mm.

[0103] The perforated layer 19 comprises a material identical to or different from the material of the honeycomb structure 18.

[0104] According to an advantageous embodiment, the perforated layer 19 and the honeycomb structure 18 form a monolithic part.

[0105] Advantageously, the porous layer 20 is multi-layered and is in the form of a lattice or mesh.

[0106] Advantageously, the porous layer 20 has a surface mass of between 30 gsm and 1000 gsm, in particular between 50 gsm and 400 gsm.

[0107] Advantageously, the porous layer 20 has a thickness of between 30 μm and 1200 μm, in particular between 50 μm and 300 μm.

[0108] Advantageously, the porous layer 20 comprises a textile layer, in particular a woven layer, comprising threads advantageously comprising a polymeric material chosen for example from thermoplastics. The thermoplastic material is for example chosen from polyaryletherketones (PAEK) such as a polyetherketone (PEK), a polyetheretherketone (PEEK) or a polyetherketoneketone (or PEKK) or polyacrylonitrile fibers (PAN) such as the HexTow® AS4, AS7 or IM7 fibers marketed by the company Hexcel. According to another example, the threads comprise a metallic material such as aluminum or a ceramic material. The porous layer 20 is fixed to the perforated layer 19. Preferably, the porous layer 20 is fixed to the perforated layer 19 by entanglement of the porous layer 20 in the perforated layer 19. By entanglement, it is meant an at least partial coating of the wires of the porous layer 20 in the material of the perforated layer 19.Thus, the wires of the porous layer 20 are arranged at least partially in the thickness of the perforated layer 19.

[0109] The honeycomb structure 18 according to the invention makes it possible to improve the acoustic attenuation performance of the acoustic panel 17 in terms of frequency range and / or level without increasing the height h1 of the honeycomb structure 18.

[0110] Indeed, the slot system 23 provided on the peripheral wall 22 of the acoustic cell 21 receiving the first partition 24 and the first lug 26 provided on the first partition 24 constitutes a mechanical attachment facilitating the integration of such a first partition 24.

[0111] Such mechanical anchoring eliminates the need for tedious and costly welding, soldering or gluing of partitions.

[0112] The manufacture of the honeycomb structure 18 is thus simple and quick to manufacture and therefore inexpensive.

[0113] According to another embodiment illustrated in Figure 15, the cellular structure 18 comprises an acoustic cell 21 having a cavity 21a delimited by a peripheral wall 22. The cellular structure 18 further comprises a first partition 24 arranged in the cavity 21a. According to this embodiment, the first partition 24 has a first acoustically permeable membrane 25 extending transversely to the first direction Y and first lugs 26 received in a respective first slot 23 formed in the peripheral wall 22 to mechanically fix the first partition 24. The first partition 24 further comprises separators 22' extending into the cavity 21a.

[0114] The separators 22' make it possible to create honeycomb cells in a simple manner. According to this embodiment, the honeycomb structure 18 further comprises a second partition 24' comprising a secondary membrane 25' fixed to the separators 22' of the first partition 24. The secondary membrane 25' can be fixed to the separators 22' by any fixing means F such as welding, gluing.

Claims

CLAIMS 1. Honeycomb structure (18) for an acoustic panel (17) of an aircraft turbomachine (1), the honeycomb structure (18) comprising: - at least one acoustic cell (21), the acoustic cell (21) comprising a cavity (21a) and a peripheral wall (22) delimiting the cavity (21), the peripheral wall (22) extending in a first direction (Y), and - at least one first partition (24) arranged in the cavity (21 a) to separate the cavity (21 a) in two along the first direction (Y), the first partition (24) comprising a first acoustically permeable membrane (25) extending transversely to the first direction (Y), the first partition (24) further comprises first lugs (26), each first lug (26) being received in a respective first slot (23) formed in the peripheral wall (22) to mechanically fix the first partition (24) in the corresponding cavity (21 a), characterized in that the first membrane (25) has a polygonal shape having peripheral edges (25a) connected by vertices (25b), the first lugs (26) extending respectively along the first direction (Y) from the vertices (25b) of the first membrane (25).

2. Alveolar structure according to the preceding claim, characterized in that the first membrane (25) has a planar shape complementary to a cross section of the cavity (21 a).

3. Honeycomb structure according to any one of the preceding claims, characterized in that the first membrane (25) has a hexagonal, square or rectangular shape.

4. Honeycomb structure according to the preceding claim, characterized in that the first membrane (25) comprises a first skin (25c) surrounded by the peripheral edges (25a), the first skin (25c) being a lattice or having holes.

5. Honeycomb structure according to one of claims 1 to 3, characterized in that the first membrane (25) comprises a first acoustically impermeable skin (25c) and at least one peripheral opening (25d).

6. Honeycomb structure according to any one of the preceding claims, characterized in that the first partitions (24) fit into each other to connect the first partitions (24) together.

7. Honeycomb structure according to any one of the preceding claims, characterized in that it further comprises a second partition (28) arranged in the cavity (21 a), the first and second partitions (24, 28) being offset in the first direction (Y) to separate the cavity (21 a) into three, the second partition (28) comprising a second acoustically permeable membrane (29) extending transversely to the first direction (Y) and second lugs (30) received respectively in a second slot (30') formed on the peripheral wall (22) to mechanically fix the second partition (28) in the corresponding cavity (21 a).

8. Alveolar structure according to the preceding claim, characterized in that the first and second membranes (25, 29) respectively comprise first and second transversely opposite peripheral openings (31, 32) to allow propagation of the sound waves in the cavity (21 a) by baffle effect.

9. Honeycomb structure according to one of claims 7 or 8, characterized in that it comprises a third partition (33) arranged in the cavity (21 a), the first, second and third partitions (24, 28, 33) being offset in the first direction (Y) to separate the cavity into four, the third partition (33) comprising a third acoustically permeable membrane (34) extending transversely to the first direction (Y) and third lugs (35) received in respective third slots (36) to mechanically fix the third partition (33) in the corresponding cavity (21 a).

10. Honeycomb structure according to the preceding claim, characterized in that the third membrane (34) comprises a mesh or a perforated layer.

11. Acoustic panel (17) for an aircraft turbomachine (1), characterized in that it comprises: - a porous layer (20), - a perforated layer (19), and - a honeycomb structure (18) according to any one of the preceding claims, the perforated structure (19) being arranged in a sandwich between the porous layer (20) and the honeycomb structure (18).

Images