Honeycomb structure for an acoustic panel

Abstract

The invention relates to a honeycomb structure for an acoustic panel comprising: - at least one acoustic cell comprising a cavity delimited by a peripheral wall, and - at least one first partition (24) arranged in the cavity to divide the cavity in two, the first partition (24) comprising a first acoustically permeable membrane (25), characterized 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 fix the first partition (24) in the corresponding cavity. Abbreviated figure: Figure 5

Description

Title of the invention: HONEYCOMB STRUCTURE FOR AN ACOUSTIC PANEL Technical field of the invention

[0001] The invention relates to the field of honeycomb structures for acoustic panels of aircraft turbomachinery. Technical background

[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 blower, 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 fan casing and defining a portion of the secondary flow v2.

[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 from an inner edge to an outer edge in a first direction parallel to the propagation of sound waves in each acoustic cell. Each acoustic cell further includes a cavity delimited by the peripheral wall and in which these sound waves propagate.

[0011] The number of honeycomb structures in the acoustic panel determines its acoustic performance 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 or triple honeycomb structures have thus been proposed.

[0012] Typically, a double-cell acoustic panel, also known by the English acronym DDOF for "Double Degree of Freedom," as opposed to a single-cell acoustic panel, also known by the English acronym SDOF for "Single Degree of Freedom," comprises first and second cell structures separated by a sound-permeable membrane. Each cell structure is therefore capable of attenuating sound waves over a specific and distinct frequency range. Such a configuration of the double or triple-cell acoustic panel makes it possible to broaden the frequency range of the attenuated sound waves.

[0013] However, compared to acoustic panels with a simple honeycomb structure, these panels have a greater thickness due to the superposition of the honeycomb structures.

[0014] 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 30 millimeters thick is suitable for attenuating frequencies close to 2000 Hz, and a honeycomb structure 70 millimeters thick is suitable for attenuating frequencies close to 880 Hz. Thus, to absorb low-frequency sound waves, the acoustic panels must have a significant thickness relative to the height of the acoustic cells. Such a thickness is not suitable for the compact size of turbomachinery.

[0015] In this context, document FR-A1-3070530 proposes arranging at least one partition within a cavity of an acoustic cell to separate the cavity according to the direction of sound wave propagation. According to this document, the partition creates 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 incorporating a partition within the cavities can attenuate sound waves over a lower frequency range.

[0016] Also, this document proposes adding a septum in order to increase the frequency range of the attenuated sound waves.

[0017] Despite the advantages this solution offers in terms of acoustic performance, it presents major challenges related to integrating such a partition into the cavity of the acoustic cells. Indeed, according to document FR-A1-3070530, integrating such partitions requires welding, brazing, or gluing operations that are lengthy, tedious, and particularly costly.

[0018] In this context, there is a need to provide an acoustic panel with a low thickness that can absorb sound waves over a wide range of frequencies while being simple, quick to manufacture and inexpensive. Summary of the invention

[0019] To this end, the invention proposes a honeycomb structure for an acoustic panel of an aircraft turbomachine, the honeycomb structure comprising:

[0020] - at least one acoustic cell comprising a cavity and a peripheral wall delimiting the cavity, the peripheral wall extending in a first direction, and

[0021] - at least a first partition arranged in the cavity to separate the cavity into two in the first direction, the first partition comprising a first acoustically permeable membrane extending transversely to the first direction.

[0022] The alveolar structure is remarkable in that the first partition further comprises first lugs, each first lug being received in a first respective slot formed in the peripheral wall to mechanically fix the first partition in the corresponding cavity.

[0023] The honeycomb structure according to the invention comprises at least one first partition arranged within 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 range and / or frequency level without increasing the height of the honeycomb structure.

[0024] 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 cell acoustic accommodating the partition and lug provided on the first partition constitutes a mechanical attachment facilitating the integration of such a first partition.

[0025] Such mechanical anchoring makes it possible to avoid tedious and costly operations of welding, brazing or gluing partitions.

[0026] The manufacture of the alveolar structure is thus simple and quick to manufacture and therefore inexpensive.

[0027] The invention may comprise one or more of the following features, taken individually or in combination with each other:

[0028] - the first membrane has a planar shape complementary to a cross-section transverse of the cavity,

[0029] - the first membrane has a polygonal shape having edges peripherals connected by vertices, in particular a hexagonal, square or rectangular shape,

[0030] - the first membrane comprises a first skin surrounded by the edges peripherals, the first layer being a mesh or having holes,

[0031] - the first membrane comprises a first acoustically impermeable skin and at least one peripheral opening,

[0032] - the first lugs extend respectively in the first direction from the vertices of the first membrane,

[0033] - the first partitions fit together to connect the first partitions between them,

[0034] - a second partition arranged in the cavity, the first and second partitions being offset along the first direction to divide 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 made on the peripheral wall to mechanically fix the second partition in the corresponding cavity,

[0035] - the first and second membranes respectively comprise first and secondly, transversely opposed peripheral openings to allow the propagation of sound waves within the cavity by means of a baffle effect,

[0036] - a third partition arranged in the cavity, the first, second and third partitions being offset along the first direction to divide 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,

[0037] - the third membrane comprises a mesh or a perforated layer.

[0038] The invention also relates to an acoustic panel for an aircraft turbomachine comprising:

[0039] - a porous layer,

[0040] - a perforated layer, and

[0041] - an alveolar structure according to any one of the preceding characteristics, the perforated structure being arranged in a sandwich between the porous layer and the alveolar structure. Brief description of the figures

[0042] Other features and advantages will become apparent from the following description of non-limiting embodiments of the invention with reference to the accompanying drawings in which:

[0043] [Fig. 1] is a schematic longitudinal cross-sectional representation of half an aircraft turbomachine,

[0044] [Fig.2] is a perspective representation of an acoustic panel according to the invention,

[0045] [Fig. 3] is a perspective representation of an acoustic cell according to an embodiment of the invention,

[0046] [Fig. 4] is a perspective representation of an acoustic cell according to another embodiment of the invention,

[0047] [Fig. 5] is a schematic representation of a first partition according to an example of an embodiment of the invention,

[0048] [Fig. 6] is a schematic representation of a first partition according to another embodiment of the invention,

[0049] [Fig. 6a] is a schematic representation of a first partition according to another embodiment of the invention,

[0050] [Fig.7] is a perspective representation of an alveolar structure according to an embodiment of the invention,

[0051] [Fig.8] is a longitudinal sectional representation of a peripheral wall of the alveolar structure of [Fig.7],

[0052] [Fig.9] is a schematic representation of the first partitions equipping the alveolar structure of [Fig.7],

[0053] [Fig. 10] is a perspective representation of an acoustic cell in which first and second partitions are arranged according to another embodiment of the invention,

[0054] [Fig.11] is a cross-sectional representation of the acoustic cell of [Fig.10],

[0055] [Fig. 12] is a perspective representation of one of the partitions equipping the acoustic cell of the [Fig. 10],

[0056] [Fig.13] is a cross-sectional representation of one of the partitions of [Fig.10],

[0057] [Fig. 14] is a cross-sectional representation of an acoustic cell in which are arranged with the first, second and third partitions according to another embodiment of the invention,

[0058] [Fig. 15] is a cross-sectional representation of an alveolar structure according to another embodiment of the invention. Detailed description of the invention

[0059] An example of a turbomachine 1 for an aircraft is shown in [Fig. 1]. The turbomachine 1 extends around and along a longitudinal axis A.

[0060] In the present application, the terms "upstream" and "downstream" are defined with respect to the direction of gas flow in the turbomachine 1 along the longitudinal axis A.

[0061] The terms “axial”, “axially”, “radial”, “radially” are defined with respect to the longitudinal axis A.

[0062] The terms "internal", "interior", "internally", "external", "exterior", "externally", are defined with respect to the distance from the longitudinal axis A along an axis Z perpendicular to the longitudinal axis A.

[0063] The turbomachine 1 is preferably a turbojet, for example a twin-spool, twin-spool 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 an exhaust nozzle.

[0064] The low-pressure and high-pressure compressors 3, 4 and the high-pressure 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.

[0065] The blower 2 comprises a rotating disc about the longitudinal axis A and blades 10 extending radially from the disc. The blower 2 further comprises a blower shaft (not shown) connected to the low-pressure shaft 8 via, for example, a speed reducer.

[0066] The blower 2 allows the intake of an airflow F which splits into a primary airflow Fl and a secondary airflow F2. The primary airflow Fl passes through a primary channel v1 of the turbomachine 1 and the secondary airflow F2 flows into a channel secondary v2 of turbomachine 1. The secondary vein v2 surrounds the primary vein vl.

[0067] The primary flow Fl is compressed within the low pressure compressor 3 and 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 whose cross-section allows the acceleration of these gases to generate propulsion.

[0068] 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 flow v2.

[0069] The turbomachine 1 further includes an intermediate casing 12. The intermediate casing 12 is arranged downstream of the fan casing 11. It is connected to the fan casing 11 for example by flanges.

[0070] The intermediate casing 12 is centered on the longitudinal axis A and comprises an inner ferrule 13 and an outer ferrule 14 connected by arms 15. The outer ferrule 14 is annular and centered on the longitudinal axis A. It is arranged coaxially around the inner ferrule 13. The outer ferrule 14 delimits with the inner ferrule 13 a portion of the secondary vein v2.

[0071] The turbomachine 1 further comprises a nacelle 16. The nacelle 16 is arranged around the fan and intermediate housings 11, 12.

[0072] In order to reduce the noise pollution generated by the turbomachine 1, the turbomachine 1 comprises at least one and advantageously several 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.

[0073] 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 blower housing 11 and / or inside the outer shell 14 of the intermediate housing 12 and / or inside the nacelle 16.

[0074] With reference to [Fig. 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.

[0075] 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 inside, the perforated acoustic structure 19 being located radially between the alveolar and porous layers 18, 20.

[0076] Advantageously, the acoustic panel 17 has a thickness el along a first direction Y parallel to the propagation of sound waves in the acoustic panel 17 of between 10 mm and 100 mm, in particular between 20 mm and 50 mm.

[0077] Advantageously, the alveolar structure 18 has a height hl such as measured along the first direction Y between 10 mm and 100 mm, in particular between 10 mm and 60 mm.

[0078] The honeycomb structure 18 includes for example a metallic material such as aluminium, in particular an aluminium alloy chosen from the 6000 series or a polymeric material chosen for example from thermoplastics or composites.

[0079] 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 together to form a honeycomb structure. Each acoustic cell 21 comprises a peripheral wall 22 and a cavity 21a delimited by the peripheral wall 22.

[0080] The peripheral walls 22 extend along the first Y direction over the entire height of the honeycomb 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 along the first Y direction from the perforated layer 19. Advantageously, the outer edge 22b of at least one acoustic cell 21 has threaded holes (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 that extend between the inner edge 22a and the outer edge 22b.

[0081] 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 [Fig. 2], or hexagonal as illustrated in [Fig. 3], or even square as illustrated in [Fig. 4]. The cross-section of the acoustic cells 21 may differ from one acoustic cell 21 to another.

[0082] According to the invention, each peripheral wall 22 further comprises at least one first slot 23.

[0083] According to a first example illustrated in figures 3 and 4, each peripheral wall 22 comprises a plurality of slots 23 which are preferentially provided in the edges 22d of each peripheral wall 22. The slots 23 have, for example, an elongated shape along the first direction Y.

[0084] According to another example illustrated in figures 7 and 8, each peripheral wall 22 includes 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 inner or outer edge 22a, 22b.

[0085] The cavities 21a have diameters ranging from 8 mm to 100 mm, in particular from 10 mm to 60 mm.

[0086] According to the invention, the honeycomb 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 into two along the first direction Y. As more clearly seen in Figures 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.

[0087] Advantageously, the first membranes 25 comprise a polymeric material chosen for example from thermoplastics or thermosets, a metallic material, a ceramic material or a mixture of these.

[0088] Each first membrane 25 extends along 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 shape, a hexagonal shape as illustrated in [Fig. 5] or a rectangular shape as illustrated in [Fig. 6] or a combination thereof.

[0089] 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.

[0090] According to the invention, each first membrane 25 is acoustically permeable. The acoustic permeability of the first membranes 25 differs advantageously from the acoustic permeability of the peripheral walls 22 in order to increase the frequency range of sound wave attenuation of the acoustic panel 17.

[0091] According to a first example, the skin 25c is a lattice. The peripheral edges 25a are, for example, overmolded onto the skin 25c.

[0092] According to another example, the skin 25c has holes for the passage of sound waves. The holes have, for example, a diameter between 0.1 mm and 5 mm, in particular between 0.1 mm and 2 mm. The openness ratio of the skin 25c is, for example, between 1% and 6%. The openness ratio corresponds to the ratio between the open area and the total area of ​​the skin 25c.

[0093] According to yet another example illustrated in [Fig. 6a], the skin 25c is acoustically impermeable. The skin 25c is said to be "solid". In other words, the skin 25c has no openings. According to this embodiment, the membrane 25 further includes a peripheral opening 25d for the passage of sound waves.

[0094] Thus, each first membrane 25 forms a septum and allows the acoustic cell 21 in which it is arranged to attenuate sound waves over a wide frequency range, in particular two distinct frequency ranges without increasing the height hl of the alveolar structure 18.

[0095] Each first lug 26 is received in a respective first slot 23 to mechanically fix the first partition 24 in the corresponding cavity 21a. Such an anchoring method for the first partitions 24 eliminates the need for a tedious step of gluing, welding, or brazing the first partitions 24, thus facilitating the assembly of the first partitions 24 in the acoustic cells 21.

[0096] Advantageously, the first lugs 26 extend along the first direction Y from each vertex 25b of the membrane 25 to a free end 26a of anchoring opposite the membrane 25.

[0097] Preferably, with reference to [Fig. 9], the first partitions 24 interlock. They are, for example, joined together by interlocking. Thus, the first partitions 24 have, for example, tongues 27 that fit into grooves in adjacent partitions 24. Such an embodiment allows the first partitions 24 to be pre-assembled before their installation in the acoustic cells 21.

[0098] According to a particularly advantageous embodiment illustrated in [Fig. 10], the alveolar structure 18 further comprises a second partition 28 arranged in at least one cavity 21a to divide said cavity 21a into three. The first and second partitions 24, 28 are thus offset along the first direction Y. Advantageously, the alveolar structure 18 comprises a plurality of second partitions 28.

[0099] 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.

[0100] Each second membrane 29 extends along the second direction X, which is 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.

[0101] As can be seen in [Fig. 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.

[0102] Advantageously, the second membranes 29 comprise a polymeric material chosen for example from thermoplastics or thermosets, a metallic material, a ceramic material or a mixture of these.

[0103] 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.

[0104] As more clearly seen in [Fig.1 1], each second lug 30 is received in a second respective slot 30' in the peripheral wall 22 to mechanically fix the second partition 28 in the corresponding cavity 21a.

[0105] As more clearly seen in [Fig.13], advantageously, the second lugs 30 extend along the first direction Y from each vertex 29b of the second membrane 29 to a free end 30a of anchorage opposite the membrane 30.

[0106] Optionally, to facilitate the assembly of the second partitions 28, the second partitions 28 fit together. For example, they are joined together by interlocking.

[0107] According to the embodiment illustrated in [Fig. 10], the first and second partitions 24, 28 respectively comprise first and second peripheral openings 31, 32 that are transversely opposed. The first and second openings 31, 32 are located between the peripheral edge 25a, 29a, and the skin 25c, 29c.

[0108] 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 sound waves. The sound waves pass through the first and second partitions 24, 28 via the first and second peripheral openings 31, 32.

[0109] 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, along a T-shaped S-shaped path. Thus, for the same cavity height 21a, the distance traveled by the sound waves is greater in 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 lower frequencies, typically below 1000 Hz, without increasing the height of the acoustic cells 21.

[0110] According to a particularly advantageous embodiment illustrated in [Fig. 14], the honeycomb structure 18 further comprises at least one third partition 33 arranged in a cavity 21a comprising the first and second partitions 24, 28 to divide said cavity 21a into four. The first, second, and third partitions 24, 28, 33 are thus offset along the first direction Y. Advantageously, the honeycomb structure 18 comprises a plurality of third partitions 28.

[0111] Each third partition 33 includes a third membrane 34 and third lugs 35 for connection to the peripheral wall 22 of each acoustic cell 21.

[0112] Each third membrane 34 extends along the second direction X. Each third membrane 34 has a planar shape complementary to the section transverse of the corresponding cavity 21a. Thus, the third membranes 34 may, for example, have a rectangular, hexagonal, square, or a combination thereof shape. 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 may, for example, be overmolded onto the skin 34c.

[0113] 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 of these.

[0114] 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.

[0115] 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.

[0116] Advantageously, the third lugs 35 extend along the first direction Y from each vertex of the third membrane 34 to a free anchoring end opposite the membrane 34.

[0117] Optionally, to facilitate the assembly of the third partitions 33, the third partitions 33 interlock with each other. For example, they are joined together by interlocking.

[0118] According to the embodiment illustrated in [Fig. 14], the first and second partitions 24, 28 respectively comprise the first and second transversely opposed peripheral openings 31, 32, and the skin 34c of the third membrane 34 is acoustically permeable. It comprises a mesh or holes for the passage of sound waves.

[0119] 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 along 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, thereby allowing the absorption of lower frequency sound waves without increasing the height of the acoustic cells 21. In combination with this baffle effect, which attenuates low frequency sound waves, the third partition 33 makes it possible to increase the frequency range of the absorbed sound waves.

[0120] The perforated layer 19 is located between the porous layer 20 and the alveolar 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.

[0121] Advantageously, the perforated layer 19 has a thickness less than the thickness of the alveolar structure 18. The thickness of the perforated layer 19 is between 0.5 mm and 2 mm.

[0122] The perforated layer 19 comprises a material identical or different from the material of the honeycomb structure 18.

[0123] According to an advantageous embodiment, the perforated layer 19 and the alveolar structure 18 form a monolithic part.

[0124] Advantageously, the porous layer 20 is multilayered and is in the form of a lattice or mesh.

[0125] Advantageously, the porous layer 20 has a surface mass between 30 gsm and 1000 gsm, in particular between 50 gsm and 400 gsm.

[0126] Advantageously, the porous layer 20 has a thickness between 30 pm and 1200 pm, in particular between 50 pm and 300 pm.

[0127] Advantageously, the porous layer 20 comprises a textile layer, particularly a woven one, comprising yarns advantageously including a polymeric material selected, for example, from thermoplastics. The thermoplastic material is, for example, selected from polyaryletherketones (PAEKs) such as polyetherketone (PEK), polyetheretherketone (PEEK), or polyetherketoneketone (PEKK), or from polyacrylonitrile (PAN) fibers such as HexTow® AS4, AS7, or IM7 fibers marketed by Hexcel. According to another example, the yarns comprise a metallic material such as aluminum or a ceramic material.

[0128] The porous layer 20 is attached to the perforated layer 19. Preferably, the porous layer 20 is attached to the perforated layer 19 by entanglement of the porous layer 20 in the perforated layer 19. By entanglement, it is understood that at least partial encapsulation of the fibers of the porous layer 20 in the material of the perforated layer 19. Thus, the fibers of the porous layer 20 are arranged at least partially within the thickness of the perforated layer 19.

[0129] 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 range and / or frequency level without increasing the height hl of the honeycomb structure 18.

[0130] Indeed, the slot system 23 provided on the peripheral wall 22 of the acoustic cell 21 housing the first partition 24 and the first lug 26 provided on the The first partition 24 constitutes a mechanical attachment facilitating the integration of such a first partition 24.

[0131] Such mechanical anchoring makes it possible to avoid tedious and costly operations of welding, brazing or gluing partitions.

[0132] The manufacture of the alveolar structure 18 is thus simple and quick to manufacture and therefore inexpensive.

[0133] According to another embodiment illustrated in [Fig. 15], the honeycomb structure 18 comprises an acoustic cell 21 having a cavity 21a delimited by a peripheral wall 22. The honeycomb 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 in the first Y direction and first lugs 26 received in a respective first slot 23 formed in the peripheral wall 22 for mechanically fixing the first partition 24. The first partition 24 further comprises separators 22' extending in the cavity 21a.

[0134] The 22' separators allow for the creation of alveolar cells in a simple manner.

[0135] 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 by welding, gluing.

Claims

Demands

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 along a first direction (Y), and - at least one first partition (24) arranged in the cavity (21a) to divide the cavity (21a) 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 comprising first lugs (26), each first lug (26) being received in a respective first slot (23) formed in the peripheral wall (22) for mechanically fixing the first partition (24) in the corresponding cavity (21a),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 (21a).

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

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

5. Alveolar structure according to any 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 one another to connect the first partitions (24) together.

7. A honeycomb structure according to any one of the preceding claims, characterized in that it further comprises a second partition (28) arranged in the cavity (21a), the first and second partitions (24, 28) being offset along the first direction (Y) to separate the cavity (21a) 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 (21a).

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

9. A honeycomb structure according to any one of claims 7 or 8, characterized in that it comprises a third partition (33) arranged in the cavity (21a), the first, second and third partitions (24, 28, 33) being offset along 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) for mechanically fixing the third partition (33) in the corresponding cavity (21a).

10. Alveolar structure according to the preceding claim, characterized in that the third membrane (34) comprises a lattice 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).