Sound absorption structure and aircraft

Abstract

The invention relates to a sound absorption structure and an aircraft. The sound absorbing structure comprises at least one honeycomb structure (52) comprising at least one partition enclosure (62) fixed in one of the cells (60) of the honeycomb structure (52) and connected to at least one partition (58) delimiting said cell (60), the partition enclosure (62) separates an inner region (ZI) located inside the partition enclosure (62) from an outer region (ZE) located in the unit (60) and outside the partition enclosure (62), the partition enclosure (62) comprising at least one through-hole (70) configured to communicate the inner region (ZI) with the outer region (ZE). This configuration makes it possible to simply define several regions in the same cell, thereby helping to increase the spectrum of attenuating acoustic waves. The aircraft comprises at least one such sound absorbing structure.

Description

Technical Field

[0001] This application relates to a honeycomb sound-absorbing structure including at least one partition enclosure positioned in a cell of a honeycomb structure, and to an aircraft including at least one such sound-absorbing structure. Background Technology

[0002] In one prior art embodiment, the aircraft propulsion assembly includes a cabin and a bypass turbojet engine located within the cabin. The bypass turbojet engine has a main jet at its rear, through which combustion gases produced by combustion are exhausted. The main jet includes sound-absorbing structures at the level of its skin to attenuate noise in multiple frequency bands, such as, for example, a band of combustion-related noise (300 Hz to 1000 Hz) and a band of turbine-related noise (greater than or equal to 4000 Hz).

[0003] In a first embodiment, the sound-absorbing structure includes at least one honeycomb structure positioned between an acoustically resistive layer and a reflective layer in contact with a medium through which sound waves propagate. This embodiment enables the creation of a quarter-wave resonator suitable for attenuating high-frequency sound waves. In this embodiment, the range of frequencies of the attenuated sound waves depends on the height of the cells in the honeycomb structure.

[0004] exist Figure 1 In the second embodiment seen in [reference to document FR094668] and described in document FR094668, the sound-absorbing structure 10 includes a first honeycomb structure 12 and a second honeycomb structure 14 positioned between an acoustically resistive layer 16 and a reflective layer 18 in contact with the medium through which sound waves propagate. The sound-absorbing structure 10 includes a partition layer 20 located between the first honeycomb structure 12 and the second honeycomb structure 14, the first honeycomb structure 12 being located between the acoustically resistive layer 16 and the partition layer 20, and the second honeycomb structure 14 being located between the reflective layer 18 and the partition layer 20.

[0005] In this second embodiment, the partition layer 20 includes openings 22, thereby enabling the cells of the first honeycomb structure 12 to communicate with the cells of the second honeycomb structure 14, each opening 22 extending from a tube 24 positioned in the second honeycomb structure 14.

[0006] The sound-absorbing structure 10 enables the acquisition of two types of resonators: a Helmholtz-type first resonator located at the level of the unit of the first honeycomb structure 12, which is suitable for attenuating low-frequency sound waves, and a quarter-wave type second resonator located at the level of the unit of the second honeycomb structure 14, which is suitable for attenuating high-frequency sound waves.

[0007] In the second embodiment, each tube 24 is connected to the partition layer via connector 24.1, and the first honeycomb structure 12 and the second honeycomb structure 14 are connected to the partition layer 20 via connectors 12.1 and 14.1. The cells of the first honeycomb structure 12 and the cells of the second honeycomb structure 14 must be perfectly aligned such that each cell of the first honeycomb structure 12 communicates with only one cell of the second honeycomb structure 14.

[0008] While this second embodiment enables sound wave attenuation over a wider frequency range, it is not entirely satisfactory because the numerous connectors increase the mass of the sound-absorbing structure 10 and complicate its manufacturing process. The second embodiment is further complex because the cells of the first and second honeycomb structures must be perfectly aligned for optimal operation. Finally, shaping the sound-absorbing structure 10 into a curved profile proves difficult, considering the connectors 12.1, 14.1 that connect the ends of the walls defining the cells of the first and second honeycomb structures 12 and 14 to the separator layer 20. Summary of the Invention

[0009] The present invention is intended to overcome some or all of the shortcomings of the prior art.

[0010] Therefore, the present invention aims to provide a sound-absorbing structure comprising at least one honeycomb structure located between a sound-absorbing layer and a reflective layer. The honeycomb structure includes a first surface in contact with the sound-absorbing layer, a second surface in contact with the reflective layer, and a plurality of units, each of which is open at the level of the first surface and the level of the second surface, and each unit is defined by at least one spacer.

[0011] According to the present invention, the honeycomb structure includes at least one partition enclosure positioned in one of the cells of the honeycomb structure and connected to at least one partition defining the cell, the partition enclosure separating an inner region inside the partition enclosure from an outer region located in the cell and outside the partition enclosure, the partition enclosure including at least one through-hole configured to communicate between the inner region and the outer region.

[0012] This solution makes it easy to form multiple regions in the unit, each of which forms a resonator configured to attenuate acoustic waves at frequencies within a given frequency range, thereby contributing to acoustic attenuation over a wide frequency spectrum.

[0013] According to another feature, each partition enclosure includes:

[0014] At least one tubular wall, generally parallel to the dividing direction, connected to at least one divider defining the unit, and extending between a first end and a second end.

[0015] A first transverse wall is fluid-tightly connected to the tubular wall at the horizontal position of the first end.

[0016] At least one second transverse wall is fluid-tightly connected to the tubular wall at the level of the second end.

[0017] The through-hole is located at the level of the first transverse wall, and the first and second transverse walls are separated from the acoustic barrier layer and the reflective layer.

[0018] According to another feature, the tubular wall has an external cross-section that is smaller than the internal cross-section of the unit and greater than or equal to 75% of the internal cross-section of the unit.

[0019] According to another feature, the partition enclosure includes a tube having a first end connected to a first transverse wall around a through-hole and a second end located at a distance from the first transverse wall, the tube having an inner diameter substantially equal to the inner diameter of the through-hole.

[0020] According to another feature, the tube and through-hole have a channel cross-section that is less than or equal to 25% of the internal cross-section of the tubular wall.

[0021] According to another feature, each unit is defined by multiple partitions, and the partition enclosure is connected to at most two partitions that define the unit.

[0022] According to another feature, the tubular wall includes at least one flat portion configured to press against and connect to the separators of the honeycomb structure.

[0023] According to another feature, the tubular wall has a constant external cross-section located between the first transverse wall and the second transverse wall and includes a curved main portion with an approximately arcuate cross-section, a main flat portion and two secondary flat portions positioned on corresponding opposite sides of the main flat portion, thereby connecting the main flat portion to the curved main portion.

[0024] According to another feature, each element has a hexagonal cross-section inscribed in a circle within the element's diameter. Additionally, the curved main portion and two sub-flat portions are separated from the element's spacers by a distance between 5% and 50% of the element's diameter.

[0025] According to another feature, the first transverse wall and the second transverse wall are oriented toward the reflective layer and the acoustic barrier layer, respectively.

[0026] According to another feature, the first transverse wall and the second transverse wall are oriented toward the acoustic barrier layer and the reflective layer, respectively.

[0027] Another object of the present invention is to provide an aircraft comprising at least one sound-absorbing structure having any of the features described above. Attached Figure Description

[0028] Other features and advantages will become apparent from the following description of the invention, which is given by way of example only and with reference to the accompanying drawings, in which:

[0029] Figure 1 This is a schematic cross-section of a sound-absorbing structure, depicting a prior art implementation.

[0030] Figure 2 This is a side view of the aircraft.

[0031] Figure 3 It is a longitudinal section of a part of the aircraft's propulsion assembly.

[0032] Figure 4 This is a view taken from above a portion of the honeycomb structure, depicting an embodiment of the invention.

[0033] Figure 5 This is a perspective view taken from a first angle of the partition enclosure positioned in the mold, depicting one embodiment of the invention.

[0034] Figure 6 It is from Figure 5 A perspective view of the partition enclosure and mold from a second angle, as observed in the image.

[0035] Figure 7 This is a cross-section of the partition enclosure, which depicts an embodiment of the invention.

[0036] Figure 8 This is a perspective view of the partition enclosure, depicting an embodiment of the present invention.

[0037] Figure 9 This is a schematic diagram illustrating the various steps of installing the partition enclosure in a honeycomb structure unit, depicting an embodiment of the invention.

[0038] Figure 10 This is a cross-section of the sound-absorbing structure, depicting the first embodiment of the present invention.

[0039] Figure 11 This is a cross-section of the sound-absorbing structure, which depicts the second embodiment of the present invention. Detailed Implementation

[0040] exist Figure 2The image shows an aircraft 30, which has a fuselage 32, two wings 34 located on opposite sides of the fuselage 32, and propulsion assemblies 36 fixed below the wings 34. Each propulsion assembly 36 includes a cabin 38 and a turbojet engine 40 located inside the cabin 38.

[0041] exist Figure 3 In the embodiment seen, the turbojet engine 40 includes a main injection pipe 42 at the rear through which the gases burned in the turbojet engine 40 escape, and the main injection pipe 42 is defined on the outer side by an outer wall 44 and on the inner side by an inner wall 46 extending through a tapered member 48.

[0042] In one configuration, the outer wall 44 and the inner wall 46 each include at least one sound-absorbing structure 50.

[0043] Each sound-absorbing structure 50 includes an outer surface SE in contact with the medium through which sound waves propagate and an inner surface SI opposite to the outer surface SE.

[0044] Although described as being applied to the main jet pipe 42, the invention is not limited to this application. Therefore, the sound-absorbing structure 50 can be positioned at the level of a wall having an outer surface SE that contacts the medium through which sound waves propagate.

[0045] like Figure 3 , Figure 10 and Figure 11 As depicted, each sound-absorbing structure 50 includes at least one honeycomb structure 52 located between a sound-resistant layer 54 that is permeable to sound waves and a reflective layer 56 that is impermeable to sound waves. The sound-resistant layer 54 has a first surface 54.1 corresponding to the outer surface SE and a second surface 54.2 oriented toward and connected to the honeycomb structure 52. The reflective layer 56 has a first surface 56.1 corresponding to the inner surface SI and a second surface 56.2 oriented toward and connected to the honeycomb structure 52.

[0046] The acoustic resistive structure 54, the reflective layer 56, the connection between the acoustic resistive layer 54 and the honeycomb structure 52, and the connection between the reflective layer 56 and the honeycomb structure 52 are not described in more detail because they can be the same as the acoustic resistive structure, the reflective layer, the connection between the acoustic resistive layer and the honeycomb structure, and the connection between the reflective layer and the honeycomb structure in the prior art.

[0047] The honeycomb structure 52 extends between a first surface 52.1 that contacts the acoustic barrier layer 54 and a second surface 52.2 that contacts the reflective layer 56, and includes a plurality of spacers 58, each of which has a first edge and a second edge positioned at the level of the first surface 52.1 and the second surface 52.2, respectively. The spacers 58 are interconnected to define the cells 60 that are open at the level of the first surface 52.1 and the second surface 52.2.

[0048] exist Figure 4 and Figure 9 In the embodiment shown, the honeycomb structure 52 is defined by a plurality of walls. For example... Figure 10 As depicted, each cell 60 is part of a honeycomb structure defined by six generally rectangular dividers 58 and has a hexagonal cross-section with six identical sides. Each hexagonal cell 60 is inscribed in a circle with a cell diameter D60. The cell diameter is between 9.6 mm and 19.1 mm. Each cell 60 has a cell height H60, which corresponds to the distance separating the first face 52.1 and the second face 52.2. The cell height H60 is between 30 mm and 70 mm. Each rectangular divider 58 has a length equal to the cell height H60, between 30 mm and 70 mm, and a width between approximately 5 mm and 12 mm.

[0049] Of course, the invention is not limited to this embodiment of unit 60. Each unit is open at the level of a first end and a second end, which are respectively blocked by the acoustic blocking layer 54 and the reflective layer 56. Each unit 60 is defined by at least one separator 58 parallel to the separation direction DL, which is substantially perpendicular to the acoustic blocking layer 54 and / or the reflective layer 56.

[0050] like Figure 4 , Figures 9 to 11 As depicted, the honeycomb structure 52 includes a system of at least one partition positioned within cells 60 of the honeycomb structure 52 and configured to divide the cells 60 of the honeycomb structure 52 into a plurality of chambers. The system of partitions includes partition enclosures 62 positioned within the cells 60. In one configuration, the honeycomb structure 52 includes a plurality of partition enclosures 62, each partition enclosure 62 being positioned within a cell 60. In one arrangement, in at least one region of the honeycomb structure 52, the honeycomb structure 52 includes a partition enclosure 62 in each cell 60.

[0051] Each partition enclosure 62 includes: at least one tubular wall 64 extending generally parallel to the partition direction DL, the tubular wall 64 extending between a first end 64.1 and a second end 64.2; a first transverse wall 66 connected to the tubular wall 64 at the level of the first end 64.1; and at least one second transverse wall 68 connected to the tubular wall 64 at the level of the second end 64.2. The tubular wall 64, the first transverse wall 66, and the second transverse wall 68 are fluid-tightly connected to each other to separate the inner region ZI and the outer region ZE. The first transverse wall 66 and the second transverse wall 68 are generally parallel to each other and generally parallel to the acoustic barrier layer 54 and / or the reflective layer 56, and are spaced apart from the acoustic barrier layer 54 and the reflective layer 56. Therefore, the partition enclosure 62 is located at a distance from the acoustic barrier layer 54 and the reflective layer 56.

[0052] The tubular wall 64 has a constant external cross-section (in a plane parallel to the acoustic barrier layer 54 and / or reflective layer 56) between the first transverse wall 66 and the second transverse wall 68. The first transverse wall 66 and the second transverse wall 68 are substantially perpendicular to the tubular wall 64. The external cross-section of the tubular wall 64 is smaller than and greater than or equal to 75% of the internal cross-section of the unit 60 in which the partition enclosure 62 is positioned. This configuration allows for a reduced passage between the partition enclosure 62 and the partition 58 of the unit 60, thereby enabling the first chamber CH1 and the second chamber CH2 to be defined on corresponding opposite sides of the partition enclosure 62.

[0053] The partition enclosure 62 includes at least one through-hole 70 located at the level of the tubular wall 64, the first transverse wall 66, or the second transverse wall 68. In one embodiment, the through-hole 70 is located at the level of the first transverse wall 66 and is substantially centered relative to the tubular wall 64.

[0054] In one configuration, the partition enclosure 62 includes a tube 72 having a first end 72.1 connected to a first transverse wall 66 around a through-hole 70 and a second end 72.2 located at a distance from the first transverse wall 66. The tube 72 is generally parallel to the partition direction DL and is generally centered relative to the tubular wall 64. The tube 72 has an inner diameter that is generally equal to the inner diameter of the through-hole 70.

[0055] The tube 72 and the through-hole 70 have a channel cross-section less than or equal to 25% of the internal cross-section of the tubular wall 64. The tube 72 has a constant cylindrical cross-section between its two ends. The tube 72 is approximately perpendicular to the first transverse wall 66. To give an order of magnitude, the tube 72 has an inner diameter between 0.5 mm and 5 mm and a height between 1 mm and 15 mm (the distance between the ends of the tube 72).

[0056] Each partition enclosure 62 is made into a single piece, with the first transverse wall 66 and the second transverse wall 68, the tubular wall 64 and the tube 72 produced in the same production steps.

[0057] In one embodiment, the partition enclosure 62 is made of plastic material.

[0058] In one operating mode, each partition enclosure 62 is produced using a mold 74 via a blow molding-extrusion-molding process, the mold 74 having an internal shape identical to the external shape of the partition enclosure 62.

[0059] This blow molding-extrusion-molding process enables the high-productivity production of the partition enclosure 62. The process also allows for easy modification of the cross-section and / or height of the tubular wall 64 by adjusting the shape of the mold 74.

[0060] Of course, the present invention is not limited to this mode of operation. By way of example, the partition 62 can be manufactured by injection molding or any other process.

[0061] The honeycomb structure 52, including each partition enclosure 62, includes at least one connector 76 connecting the tubular walls 64 of the partition enclosure 62 and at least one partition 58 defining the cells 60 in which the partition enclosure 62 are positioned. The connector 76 may be obtained by gluing, clamping, welding or other means.

[0062] In one embodiment, the tubular wall 64 includes at least one flat portion 78 configured to press against the divider 58 of the honeycomb structure 52 and connected to the divider 58 via a connector 76. In one configuration, each flat portion 78 extends the entire height of the tubular wall 64 (the dimension from one transverse wall 66, 68 to another transverse wall).

[0063] Connecting the tubular wall 64 to only one separator 58 of the honeycomb structure 52 allows for considerable flexibility at the horizontal level of the honeycomb structure 52. Alternatively, the separator enclosure 62 may include two flat portions connected to two separators. To maintain some flexibility, the separator enclosure 62 may be connected to at most two separators 58 of the unit 60.

[0064] Additionally, the tubular wall 64 has a curved main portion 80 with a generally arcuate cross section that extends the entire height of the tubular wall 64 (the dimension from one transverse wall 66, 68 to another transverse wall).

[0065] In the case of the hexagonal cross-section unit 60, the tubular wall 64 includes a main flat portion 78 and two secondary flat portions 82.1, 82.2, which are positioned on corresponding opposite sides of the main flat portion 78, thereby connecting the main flat portion 78 to the curved main portion 80. This solution allows for the provision of gaps between the other gaps 58 of one side of the unit 60 and the curved main portion 80 and the secondary flat portions 82.1, 82.2 of the tubular wall 64, when the main flat portion 78 is fixed to one of the partitions 58 of the hexagonal unit 60.

[0066] To give an order of magnitude, the sub-flat portions 82.1 and 82.2 form an angle between 40° and 140° with each other. This angle is determined such that each of the sub-flat portions 82.1 and 82.2 is approximately parallel to one of the spacers 58 of unit 60. Furthermore, outside the main flat portion 78 that presses against one of the spacers 58 of unit 60, the curved main portion 80 and the two sub-flat portions 82.1 and 82.2 are separated from the spacers 58 of unit 60 by a distance between 5% and 50% of the diameter D60 of unit 60.

[0067] In one arrangement, the first transverse wall 66 or the second transverse wall 68 closest to the acoustic resistive layer 54 is separated from the acoustic resistive layer 54 by a distance of 5 mm and 70% of the height H60 of the unit 60. For a unit height H60 between 30 mm and 70 mm, the tubular wall 64 has a height between 10 mm and 40 mm (the dimension from one transverse wall 66, 68 to the other transverse wall).

[0068] Of course, the present invention is not limited to this embodiment. Regardless of the embodiment, the honeycomb structure 52 includes at least one partition enclosure 62, which is positioned in a cell 60 of the honeycomb structure 52 and connected to at least one partition 58 defining the cell 60. The partition enclosure 62 separates an inner region ZI located inside the partition enclosure 62 and an outer region ZE located in the cell 60 and outside the partition enclosure 62. The partition enclosure 62 includes at least one through-hole 70 configured to communicate between the inner region ZI and the outer region ZE.

[0069] exist Figure 10 In the first embodiment seen in the diagram, the first transverse wall 66 is oriented toward the reflective layer 56, and the second transverse wall 68 is oriented toward the acoustic barrier layer 54. In this case, the tube 72 is open in the direction of the reflective layer 56.

[0070] exist Figure 11In the second embodiment seen in the diagram, the first transverse wall 66 is oriented toward the acoustic barrier layer 54, and the second transverse wall 68 is oriented toward the reflective layer 56. In this case, the tube 72 is open in the direction of the acoustic barrier layer 54.

[0071] In both embodiments, the partition enclosure 62 is preferably located at a distance from the acoustic resistive layer 54 and the reflective layer 56, and is very close to the partition 58 of the unit 60 in which the partition enclosure 62 is located. Therefore, the partition enclosure 62 allows the unit 60 to be divided into a first chamber CH1 located between the acoustic resistive layer 54 and the partition enclosure 62, a second chamber CH2 located between the reflective layer 56 and the partition enclosure 62, and a third chamber CH3 located inside the partition enclosure 62. This solution allows for the acquisition of three resonators configured to absorb a wide spectrum of sound waves.

[0072] exist Figure 10 In the first embodiment seen herein, sound waves pass through the acoustic barrier layer 54 and enter the first chamber CH1, which forms a first resonator configured to absorb sound waves at frequencies within a first range. Unabsorbed sound waves pass between the separator 58 and the partition enclosure 62 of unit 60 and enter the second chamber CH2, which forms a second resonator configured to absorb sound waves at frequencies within a second range. Unabsorbed sound waves enter the partition enclosure 62 via the tube 72, thereby forming a third resonator configured to absorb sound waves at frequencies within a third range.

[0073] exist Figure 11 In the second embodiment seen in the diagram, sound waves pass through the acoustic barrier layer 54 and enter the first chamber CH1, which forms a first resonator configured to absorb sound waves at frequencies within a first range. Some unabsorbed sound waves pass between the separator 58 and the partition enclosure 62 of unit 60 and enter the second chamber CH2, which forms a second resonator configured to absorb sound waves at frequencies within a second range. Other unabsorbed sound waves enter the partition enclosure 62 via the tube 72, thereby forming a third resonator configured to absorb sound waves at frequencies within a third range.

[0074] In one production mode, the method of producing a sound-absorbing structure includes the steps of producing a honeycomb structure 52 comprising a first plane 52.1 and a second plane 52.2, inserting each partition enclosure 62 into a unit 60, fixing the partition enclosure 62 inserted into the unit 60 to at least one partition 58 of the unit 60, forming the honeycomb structure 52, and fitting the sound-resistant layer 54 and the reflective layer 56 produced after the step of fixing the partition enclosure 62 into the unit 60 of the honeycomb structure 52.

[0075] The partition enclosure 62 can be inserted one after another, one partition enclosure can be inserted after another partition enclosure is inserted, or more than one partition enclosure can be inserted at once, or multiple partition enclosures can be inserted simultaneously.

[0076] The step of inserting the partition enclosure 62 can be mechanized and / or performed before or after the forming step.

[0077] like Figure 4 As depicted, the partition enclosure 62 can be connected to the parallel partitions 58 of the honeycomb structure 52.

[0078] Of course, the present invention is not limited to this method of producing the sound-absorbing structure 50.

Claims

1. A sound-absorbing structure comprising at least one honeycomb structure (52) located between a sound-resistant layer (54) and a reflective layer (56), the honeycomb structure (52) comprising a first surface (52.1) in contact with the sound-resistant layer (54), a second surface (52.2) in contact with the reflective layer (56), and a plurality of units (60), each of the plurality of units (60) being open at the level of the first surface (52.1) and at the level of the second surface (52.2), each unit (60) being defined by at least one separator (58), characterized in that, The honeycomb structure (52) includes at least one partition enclosure (62) positioned in one of the cells (60) of the honeycomb structure (52) and connected to at least one partition (58) defining the cell (60). The partition enclosure (62) separates an inner region (ZI) inside the partition enclosure (62) from an outer region (ZE) located in the cell (60) and outside the partition enclosure (62). The partition enclosure (62) includes at least one through-hole (70) configured to communicate between the inner region (ZI) and the outer region (ZE).

2. The sound-absorbing structure according to the preceding claim, characterized in that, The partitions (58) defining the unit (60) are oriented in a partition direction (DL), and each partition enclosure (62) includes: at least one tubular wall (64) that is generally parallel to the partition direction (DL), connected to at least one partition (58) defining the unit (60) and extending between a first end (64.1) and a second end (64.2); a first transverse wall (66) that is fluid-tightly connected to the tubular wall (64) at the level of the first end (64.1); and at least one second transverse wall (68) that is fluid-tightly connected to the tubular wall (64) at the level of the second end (64.2), the through-hole (70) being located at the level of the first transverse wall (66), and the first transverse wall (66) and the second transverse wall (68) being spaced apart from the acoustic barrier layer (54) and the reflective layer (56).

3. The sound-absorbing structure according to the preceding claim, characterized in that, The unit (60) in which the partition enclosure (62) is positioned has an internal cross-section, and the tubular wall (64) has an external cross-section that is smaller than the internal cross-section of the unit (60) and greater than or equal to 75% of the internal cross-section of the unit (60).

4. The sound-absorbing structure according to any one of claims 2 or 3, characterized in that, The partition enclosure (62) includes a tube (72) having a first end (72.1) connected to the first transverse wall (66) around the through opening (70) and a second end (72.2) located at a distance from the first transverse wall (66), the tube (72) having an inner diameter substantially equal to the inner diameter of the through opening (70).

5. The sound-absorbing structure according to the preceding claim, characterized in that, The tubular wall (64) has an internal cross-section, and the tube (72) and the through-hole (70) have a channel cross-section that is less than or equal to 25% of the internal cross-section of the tubular wall (64).

6. The sound-absorbing structure according to any one of claims 2 to 5, characterized in that, Each unit (60) is defined by a plurality of partitions (58), and the partition enclosure (62) is connected to at most two partitions (58) that define the unit (60).

7. The sound-absorbing structure according to the preceding claim, characterized in that, The tubular wall (64) includes at least one flat portion (78) configured to press against and connect to the separator (58) of the honeycomb structure (52).

8. The sound-absorbing structure according to the preceding claim, characterized in that, The tubular wall (64) has a constant external cross-section between the first transverse wall (66) and the second transverse wall (68) and includes a curved main portion (80) with an arcuate cross-section, a main flat portion (78) and two secondary flat portions (82.1, 82.2) positioned on corresponding opposite sides of the main flat portion (78) to connect the main flat portion (78) to the curved main portion (80).

9. The sound-absorbing structure according to the preceding claim, characterized in that, Each unit (60) has a hexagonal cross section inscribed in a circle having a unit diameter (D60), and the curved main portion (80) and the two sub-flat portions (82.1, 82.2) are separated from the spacer (58) of the unit (60) by a distance between 5% and 50% of the unit diameter (D60).

10. The sound-absorbing structure according to any one of claims 2 to 9, characterized in that, The first transverse wall (66) and the second transverse wall (68) are oriented toward the reflective layer (56) and the acoustic barrier layer (54), respectively.

11. The sound-absorbing structure according to any one of claims 2 to 9, characterized in that, The first transverse wall (66) and the second transverse wall (68) are oriented toward the acoustic resist layer (54) and the reflective layer (56), respectively.

12. An aircraft comprising at least one sound-absorbing structure according to any one of the preceding claims.

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