Sound absorption structure comprising a honeycomb structure and at least one partition enclosure positioned in a cell of the honeycomb structure

Abstract

Acoustic absorption structure comprising a honeycomb structure and at least one partitioning enclosure positioned in a cell of the honeycomb structure The invention relates to an acoustic absorption structure comprising at least one honeycomb structure (52) which comprises at least one partitioning enclosure (62) positioned in one of the cells (60) of the honeycomb structure (52) and connected to at least one partition (58) delimiting said cell (60), said partitioning enclosure (62) separating an interior zone (ZI) located inside the partitioning enclosure (62) and an exterior zone (ZE) located in the cell (60) and outside the partitioning enclosure (62), said partitioning enclosure (62) comprising at least one through-orifice (70) configured to communicate the interior and exterior zones (ZE, ZI).This configuration makes it possible to simply delimit several zones in the same cell, helping to increase the frequency spectrum of the attenuated acoustic waves. The invention also relates to an aircraft comprising at least one such acoustic absorption structure. Figure 10.

Description

Title of the invention: Sound absorption structure comprising a honeycomb structure and at least one partitioning enclosure positioned in a cell of the honeycomb structure

[0001] The present application relates to a sound absorption structure comprising a honeycomb structure and at least one partitioning enclosure positioned in a cell of the honeycomb structure as well as to an aircraft comprising at least one such sound absorption structure.

[0002] According to an embodiment of the prior art, an aircraft propulsion assembly comprises a nacelle and a dual-flow turbomachine, positioned inside the nacelle, which has, at the rear, a primary exhaust duct through which the burnt gases resulting from the combustion are evacuated. This primary exhaust duct comprises, at its skin, an acoustic absorption structure to attenuate noise over several frequency bands, such as noises linked to combustion (300-1000 Hz) and those linked to the operation of the turbine (greater than or equal to 4000 Hz) for example.

[0003] According to a first embodiment, an acoustic absorption structure comprises at least one alveolar structure positioned between an acoustically resistive layer in contact with a medium in which acoustic waves propagate and a reflective layer. This embodiment makes it possible to obtain a wave resonator suitable for attenuating sound waves with high frequencies. According to this embodiment, the frequency range of the attenuated sound waves depends on the height of the cells of the alveolar structure.

[0004] According to a second embodiment visible in [Fig.l] and described in the document FR3094668, an acoustic absorption structure 10 comprises first and second alveolar structures 12, 14 positioned between an acoustically resistive layer 16 in contact with a medium in which acoustic waves propagate and a reflective layer 18. This acoustic absorption structure 10 comprises a separation layer 20 interposed between the first and second alveolar structures 12, 14, the first alveolar structure 12 being interposed between the acoustically resistive layer 16 and the separation layer 20, the second alveolar structure 14 being interposed between the reflective layer 18 and the separation layer 20.

[0005] According to this second embodiment, the separation layer 20 comprises orifices 22 allowing the cells of the first structure to communicate. alveolar 12 with those of the second alveolar structure 14, each orifice 22 being extended by a tube 24 positioned in the second alveolar structure 14.

[0006] The acoustic absorption structure 10 makes it possible to obtain two types of resonators, a first Helmholtz type resonator at the level of the cells of the first alveolar structure 12, adapted to attenuate low-frequency sound waves, as well as a second wave % type resonator at the level of the cells of the second alveolar structure 14, adapted to attenuate high-frequency sound waves.

[0007] According to this second embodiment, each tube 24 is connected by a connection 24.1 to the separation layer and then the first and second alveolar structures 12, 14 are connected by connections 12.1, 14.1 to the separation layer 20. The cells of the first and second alveolar structures 12, 14 must be perfectly aligned so that each cell of the first alveolar structure 12 communicates with only one cell of the second alveolar structure 14.

[0008] Even if this second embodiment makes it possible to attenuate the sound waves over wider frequency ranges, it is not fully satisfactory because the large number of connections leads to an increase in the mass of the sound absorption structure 10 and to a complication of its manufacturing process. The latter is all the more complex to implement since the cells of the first and second alveolar structures must be perfectly aligned to obtain optimal operation. Finally, shaping the sound absorption structure 10 according to a curved profile proves difficult given the connections 12.1, 14.1 which connect the ends of the walls delimiting the cells of the first and second alveolar walls 12, 14 with the separation layer 20.

[0009] The present invention aims to remedy all or part of the drawbacks of the prior art.

[0010] To this end, the invention relates to an acoustic absorption structure comprising at least one alveolar structure interposed between an acoustically resistive layer and a reflective layer, the alveolar structure comprising a first face in contact with the acoustically resistive layer, a second face in contact with the reflective layer as well as a multitude of cells each opening at the level of the first and second faces, each cell being delimited by at least one partition.

[0011] According to the invention, the cellular structure comprises at least one partitioning enclosure positioned in one of the cells of the cellular structure and connected to at least one partition delimiting the cell, said partitioning enclosure separating an interior zone located inside the partitioning enclosure and an exterior zone located in the cell and outside the partitioning enclosure, said partition enclosure comprising at least one through-hole configured to connect the interior and exterior zones.

[0012] This solution makes it possible to create, in a simple manner, several zones in a cell, each of which forms a resonator configured to attenuate acoustic waves having frequencies included in a given frequency range, thus contributing to acoustic attenuation over a wide frequency spectrum.

[0013] According to another characteristic, each partition enclosure comprises: a. at least one tubular wall substantially parallel to the partition direction, connected to at least one partition delimiting the cell, which extends between first and second ends, b. a first transverse wall tightly connected to the tubular wall at the first end, c. at least one second transverse wall tightly connected to the tubular wall at the second end, d. the through-hole being located at the first transverse wall, the first and second transverse walls being spaced from the acoustically resistive layer and the resistive layer.

[0014] According to another characteristic, the tubular wall has an external cross-section less than the internal cross-section of the cell and greater than or equal to 75% of the internal cross-section of said cell.

[0015] According to another characteristic, the partitioning enclosure comprises a conduit which has a first end connected to the first transverse wall around the through-orifice as well as a second end distant from the first transverse wall, the conduit comprising an internal diameter substantially equal to that of the through-orifice.

[0016] According to another characteristic, the conduit and the through orifice have a passage section less than or equal to 25% of the internal cross section of the tubular wall.

[0017] According to another characteristic, each cell is delimited by several partitions, the partitioning enclosure being connected to at most two partitions delimiting the cell.

[0018] According to another characteristic, the tubular wall comprises at least one flat configured to be pressed against a partition of the cellular structure and connected to the latter.

[0019] According to another characteristic, the tubular wall has a constant external cross-section between the first and second transverse walls and comprises a curved main part which has a section approximately in the shape of an arc of a circle, a main flat as well as two secondary flats positioned on either side of the main flat, connecting the latter to the curved main part.

[0020] According to another characteristic, the cells each have a hexagonal section inscribed in a circle of cell diameter. In addition, the curved main part and the two secondary flats are spaced from the partitions of the cell by a spacing of between 5 and 50% of the cell diameter.

[0021] According to another characteristic, the first and second transverse walls are oriented respectively towards the reflective layer and the acoustically resistive layer.

[0022] According to another characteristic, the first and second transverse walls are oriented respectively towards the acoustically resistive layer and the reflective layer.

[0023] The invention also relates to an aircraft comprising at least one acoustic absorption structure according to one of the preceding characteristics.

[0024] Other characteristics and advantages will emerge from the description of the invention which follows, a description given by way of example only, with reference to the appended drawings, among which:

[0025] [Fig.l] is a schematic section of an acoustic absorption structure illustrating an embodiment of the prior art,

[0026] [Fig.2] is a side view of an aircraft,

[0027] [Fig.3] is a longitudinal section of a part of a propulsion assembly aircraft,

[0028] [Fig.4] is a top view of a portion of a honeycomb structure illustrating a embodiment of the invention,

[0029] [Fig.5] is a perspective view from a first viewing angle of an enclosure partitioning positioned in a mold illustrating an embodiment of the invention,

[0030] [Fig.6] is a perspective view from a second viewing angle of the enclosure of partitioning and the mold visible in [Fig.5],

[0031] [Fig.7] is a section of a partitioning enclosure illustrating a method of realization of the invention,

[0032] [Fig.8] is a perspective view of a partitioning enclosure illustrating a embodiment of the invention,

[0033] [Fig.9] is a schematic representation of the different stages of assembly of a partition enclosure in a cell of a honeycomb structure illustrating an embodiment of the invention,

[0034] [Fig. 10] is a section of an acoustic absorption structure illustrating a first embodiment of the invention,

[0035] [Fig. 11] is a section of an acoustic absorption structure illustrating a second embodiment of the invention.

[0036] In [Fig.2], an aircraft 30 is shown which has a fuselage 32, two wings 34, arranged on either side of the fuselage 32, and propulsion units 36 fixed under the wings 34. Each propulsion unit 36 ​​comprises a nacelle 38 and a turbomachine 40 positioned inside the nacelle 38.

[0037] According to an embodiment visible in [Fig. 3], the turbomachine 40 comprises, at the rear, a primary ejection duct 42, through which burnt gases escape in the turbomachine 40, which is delimited on the outside by an outer wall 44 and on the inside by an inner wall 46 extended by a nozzle cone 48.

[0038] According to one configuration, the outer and inner walls 44, 46 each comprise at least one acoustic absorption structure 50.

[0039] Each acoustic absorption structure 50 comprises an outer surface SE in contact with a medium in which acoustic waves propagate and an inner surface SI opposite the outer surface SE.

[0040] Although described as applied to a primary ejection duct 42, the invention is not limited to this application. Thus, the acoustic absorption structure 50 can be positioned at walls which have an outer surface SE in contact with a medium in which sound waves propagate.

[0041] As illustrated in Figures 3, 10 and 11, each sound absorption structure 50 comprises at least one alveolar structure 52 interposed between an acoustically resistive layer 54 permeable to sound waves and a reflective layer 56 impermeable to sound waves. The acoustically resistive layer 54 has a first face 54.1 corresponding to the outer surface SE as well as a second face 54.2 oriented towards the alveolar structure 52 and connected to the latter. The reflective layer 56 has a first face 56.1 corresponding to the inner surface SI and a second face 56.2 oriented towards the alveolar structure 52 and connected to the latter.

[0042] The acoustically resistive layer 54, the reflective layer 56, the connection between the acoustically resistive layer 54 and the honeycomb structure 52 as well as the connection between the reflective layer 56 and the honeycomb structure 52 are not described further because they may be identical to those of the prior art.

[0043] The cellular structure 52 extends between a first face 52.1 in contact with the acoustically resistive layer 54 and a second face 52.2 in contact with the reflective layer 56 and comprises a multitude of partitions 58 which each have first and second edges positioned respectively at the level of the first and second faces 52.1, 52.2. The partitions 58 are connected to each other so as to delimit cells 60 opening at the level of the first and second faces 52.1, 52.2.

[0044] According to an embodiment visible in Figures 4 and 9, the cellular structure 52 is delimited by several walls. As illustrated in [Fig. 10], each cell 60 is a honeycomb structure delimited by six substantially rectangular partitions 58 and has a hexagonal section with six identical sides. Each hexagonal cell 60 is inscribed in a circle of cell diameter D60. The cell diameter is between 9.6 and 19.1 mm. Each cell 60 has a cell height H60 which corresponds to the distance separating the first and second faces 52.1, 52.2. The cell height H60 is between 30 and 70 mm. Each rectangular partition 58 has a length equal to the cell height H60, between 30 and 70 mm, and a width between approximately 5 and 12 mm.

[0045] Of course, the invention is not limited to this embodiment for the cells 60. Each of them opens at the level of first and second ends closed respectively by the acoustically resistive layer 54 and the reflective layer 56. Each cell 60 is delimited by at least one partition 58 parallel to a partition direction DL substantially perpendicular to the acoustically resistive layer 54 and / or to the reflective layer 56.

[0046] As illustrated in Figures 4, 9 to 11, the cellular structure 52 comprises at least one partitioning system positioned in a cell 60 of the cellular structure 52 and configured to divide it into several chambers. This partitioning system comprises a partitioning enclosure 62 positioned in a cell 60. According to one configuration, the cellular structure 52 comprises several partitioning enclosures 62 each positioned in a cell 60. According to one arrangement, in at least one zone of the cellular structure 52, the latter comprises a partitioning enclosure 62 in each cell 60.

[0047] Each partition enclosure 62 comprises at least one tubular wall 64, substantially parallel to the partition direction DL, which extends between first and second ends 64.1, 64.2, a first transverse wall 66 connected to the tubular wall 64 at the first end 64.1 and at least one second transverse wall 68 connected to the tubular wall 64 at the second end 64.2. The tubular wall 64 and the first and second transverse walls 66, 68 are connected to each other in a sealed manner in order to separate an interior zone ZI and an exterior zone ZE. The first and second transverse walls 66, 68 are substantially parallel to each other and to the acoustically resistive layer 54 and / or to the reflective layer 56, the first and second transverse walls 66, 68 being spaced from the acoustically resistive layer 54 and the resistive layer 56.Thus, the partitioning enclosure 62 is distant from the acoustically resistive layer 54 and the reflective layer 56.

[0048] The tubular wall 64 has an external cross-section (positioned in a plane parallel to the acoustically resistive layer 54 and / or to the reflective layer 56) which is constant between the first and second transverse walls 66, 68. The latter are substantially perpendicular to the tubular wall 64. The external cross-section of the tubular wall 64 is less than the internal cross-section of the cell 60 in which the partitioning enclosure 62 is positioned and greater than or equal to 75% of the internal cross-section of said cell 60. This configuration makes it possible to obtain between the partitioning enclosure 62 and the partitions 58 of the cell 60 a reduction in passage making it possible to delimit first and second chambers CH1, CH2 on either side of the partitioning enclosure 62.

[0049] The partition enclosure 62 comprises at least one through-orifice 70 located at the level of the tubular wall 64, the first transverse wall 66 or the second transverse wall 68. According to one embodiment, the through-orifice 70 is located at the level of the first transverse wall 66 and substantially centered relative to the tubular wall 64.

[0050] According to one configuration, the partition enclosure 62 comprises a conduit 72 which has a first end 72.1 connected to the first transverse wall 66 around the through-orifice 70 as well as a second end 72.2 distant from the first transverse wall 66. The conduit 72 is substantially parallel to the partition direction DL and approximately centered relative to the tubular wall 64. The conduit 72 comprises an internal diameter substantially equal to that of the through-orifice 70.

[0051] The conduit 72 and the through-orifice 70 have a passage section less than or equal to 25% of the internal cross-section of the tubular wall 64. The conduit 72 has a constant cylindrical section between its two ends. The conduit 72 is substantially perpendicular to the first transverse wall 66. To give an order of magnitude, the conduit 72 has an internal diameter of between 0.5 and 5 mm and a height (distance between its ends) of between 1 and 15 mm.

[0052] Each partition enclosure 62 is produced in a single piece, the first and second transverse walls 66, 68, the tubular wall 64 and the conduit 72 being produced during the same manufacturing step.

[0053] According to one embodiment, the partition enclosure 62 is made of plastic material.

[0054] According to one method of operation, each partition enclosure 62 is obtained by an extrusion blow molding process using a mold 74 which has internal shapes identical to the external shapes of the partition enclosure 62.

[0055] This extrusion blow molding process makes it possible to produce partition enclosures 62 at high production rates. This process also makes it possible to easily modify the section and / or the height of the tubular wall 64 by adjusting the shapes of the mold 74.

[0056] Of course, the invention is not limited to this operating mode. For example, the partitioning enclosure 62 could be produced by an injection process or any other process.

[0057] For each partitioning enclosure 62, the cellular structure 52 comprises at least one connection 76 connecting the tubular wall 64 of the partitioning enclosure 62 and at least one partition 58 delimiting the cell 60 in which the partitioning enclosure 62 is positioned. This connection 76 can be obtained by gluing, stapling, welding or other means.

[0058] According to one embodiment, the tubular wall 64 comprises at least one flat 78 configured to be pressed against a partition 58 of the cellular structure 52 and connected to the latter by the connection 76. According to one configuration, each flat 78 extends over the entire height of the tubular wall 64 (dimension taken from one transverse wall 66, 68 to the other).

[0059] Connecting the tubular wall 64 to a single partition 58 of the cellular structure 52 makes it possible to maintain a high degree of flexibility at the level of the cellular structure 52. Alternatively, the partitioning enclosure 62 could comprise two flats connected to two partitions. To maintain a certain flexibility, the partitioning enclosure 62 is connected to at most two partitions 58 of the cell 60.

[0060] In addition, the tubular wall 64 has a curved main part 80 which has a section approximately in the shape of an arc of a circle which extends over the entire height of the tubular wall 64 (dimension taken from one transverse wall 66, 68 to the other).

[0061] In the case of cells 60 of hexagonal section, the tubular wall 64 comprises a main flat 78 as well as two secondary flats 82.1, 82.2 positioned on either side of the main flat 78, connecting the latter to the curved main part 80. This solution makes it possible, when the main flat 78 is fixed on one of the partitions 58 of the hexagonal cell 60, to provide a spacing between, on the one hand, the other partitions 58 of the cell 60 and, on the other hand, the curved main part 80 and the secondary flats 82.1, 82.2 of the tubular wall 64.

[0062] To give an order of magnitude, the secondary flats 82.1, 82.2 form an angle between them of between 40 and 140°. This angle is determined so that each of the secondary flats 82.1, 82.2 is substantially parallel to one of the partitions 58 of the cell 60. Furthermore, apart from the main flat 78 which is pressed against one of the partitions 58 of the cell 60, the curved main part 80 and the two secondary flats 82.1, 82.2 are spaced from the partitions 58 of the cell 60 by a spacing of between 5 and 50% of the diameter D60 of the cell 60.

[0063] According to one arrangement, the first or second transverse wall 66, 68 closest to the acoustically resistive layer 54 is spaced from the latter by a distance of between 5 mm and 70% of the height H60 of the cell 60. For a cell height H60 of between 30 and 70 mm, the tubular wall 64 has a height (distance between the first and second transverse walls 66, 68) of between 10 and 40 mm.

[0064] Of course, the invention is not limited to this embodiment. Whatever the embodiment, the cellular structure 52 comprises at least one partitioning enclosure 62 positioned in a cell 60 of the cellular structure 52 and connected to at least one partition 58 delimiting the cell 60, said partitioning enclosure 62 separating an interior zone ZI located inside the partitioning enclosure 62 and an exterior zone ZE located in the cell 60 and outside the partitioning enclosure 62, said partitioning enclosure 62 comprising at least one through-orifice 70 configured to communicate the interior and exterior zones ZE, ZI.

[0065] According to a first embodiment visible in [Fig. 10], the first transverse wall 66 is oriented towards the reflective layer 56 and the second transverse wall 68 is oriented towards the acoustically resistive layer 54. In this case, the conduit 72 opens towards the reflective layer 56.

[0066] According to a second embodiment visible in [Fig. 1 1], the first transverse wall 66 is oriented towards the acoustically resistive layer 54 and the second transverse wall 68 is oriented towards the reflective layer 56. In this case, the conduit 72 opens towards the acoustically resistive layer 54.

[0067] According to these two embodiments and in a preferred manner, the partitioning enclosure 62 is distant from the acoustically resistive layer 54 and from the reflective layer 56 and slightly spaced from the partitions 58 of the cell 60 in which the partitioning enclosure 62 is positioned. Consequently, the partitioning enclosure 62 makes it possible to split the cell 60 into a first chamber CH1 located between the acoustically resistive layer 54 and the partitioning enclosure 62, a second chamber CH2 located between the reflective layer 56 and the partitioning enclosure 62 and a third chamber CH3 located inside the partitioning enclosure 62. This solution makes it possible to obtain three resonators configured to absorb acoustic waves over a wide spectrum.

[0068] According to the first embodiment visible in [Fig. 10], the acoustic waves pass through the acoustically resistive layer 54 and enter the first chamber CH1 which forms a first resonator configured to absorb waves acoustic waves having frequencies included in a first range. The unabsorbed acoustic waves pass between the partitions 58 of the cell 60 and the partitioning enclosure 62 and enter the second chamber CH2 which forms a second resonator configured to absorb acoustic waves having frequencies included in a second range. The unabsorbed acoustic waves then enter, via the conduit 72, the partitioning enclosure 62 which forms a third resonator configured to absorb acoustic waves having frequencies included in a third range.

[0069] According to the second embodiment visible in [Fig.l 1], the acoustic waves pass through the acoustically resistive layer 54 and enter the first chamber CH1 which forms a first resonator configured to absorb acoustic waves having frequencies included in a first range. Some unabsorbed acoustic waves pass between the partitions 58 of the cell 60 and the partitioning enclosure 62 and enter the second chamber CH2 which forms a second resonator configured to absorb acoustic waves having frequencies included in a second range. Other unabsorbed acoustic waves enter via the conduit 72 into the partitioning enclosure 62 which forms a third resonator configured to absorb acoustic waves having frequencies included in a third range.

[0070] According to a production method, a method for manufacturing an acoustic absorption structure comprises a step of producing a honeycomb structure 52 comprising first and second planar faces 52.1, 52.2, a step of inserting each partitioning enclosure 62 into a cell 60, a step of fixing the partitioning enclosure 62 inserted into the cell 60 to at least one partition 58 of the cell 60, a step of forming the honeycomb structure 52 as well as steps of placing an acoustically resistive layer 54 and a reflective layer 56 carried out after the step of fixing the partitioning enclosures 62 in the cells 60 of the honeycomb structure 52.

[0071] The step of inserting the partitioning enclosures 62 can be done individually, partitioning enclosure after partitioning enclosure, or in groups, several partitioning enclosures being inserted simultaneously.

[0072] The step of inserting the partitioning enclosures 62 can be mechanized and / or carried out before or after the forming step.

[0073] As illustrated in [Fig.4], the partitioning enclosures 62 can be connected to partitions 58 of the honeycomb structure 52 parallel to each other.

[0074] Of course, the invention is not limited to this method of producing the sound absorption structure.50.

Claims

Claims

1. Acoustic absorption structure comprising at least one alveolar structure (52) interposed between an acoustically resistive layer (54) and a reflective layer (56), the alveolar structure (52) comprising a first face (52.1) in contact with the acoustically resistive layer (54), a second face (52.2) in contact with the reflective layer (56) as well as a multitude of cells (60) each opening at the level of the first and second faces (52.1, 52.2), each cell (60) being delimited by at least one partition (58); characterized in that the cellular structure (52) comprises at least one partitioning enclosure (62) positioned in one of the cells (60) of the cellular structure (52) and connected to at least one partition (58) delimiting the cell (60), said partitioning enclosure (62) separating an interior zone (ZI) located inside the partitioning enclosure (62) and an exterior zone (ZE) located in the cell (60) and outside the partitioning enclosure (62), said partitioning enclosure (62) comprising at least one through-orifice (70) configured to communicate the interior and exterior zones (ZE, ZI).

2. Sound absorption structure according to the preceding claim, characterized in that the partitions (58) delimiting the cells (60) are oriented in a partition direction (DL), in that each partition enclosure (62) comprises at least one tubular wall (64) substantially parallel to the partition direction (DL), connected to at least one partition (58) delimiting the cell (60), which extends between first and second ends (64.1, 64.2), a first transverse wall (66) connected in a sealed manner to the tubular wall (64) at the first end (64.1) as well as at least one second transverse wall (68) connected in a sealed manner to the tubular wall (64) at the second end (64.2), the through-orifice (70) being located at the first transverse wall (66), and in that the first and second transverse walls (66, 68) are spaced from the acoustically resistive layer (54) and the resistive layer (56).

3. Sound absorption structure according to the preceding claim, characterized in that the cell (60) in which the partition enclosure (62) is positioned has a cross section interior and in that the tubular wall (64) has an exterior cross-section less than the interior cross-section of the cell (60) and greater than or equal to 75% of the interior cross-section of said cell (60).

4. Sound absorption structure according to one of claims 2 to 3, characterized in that the partition enclosure (62) comprises a conduit (72) which has a first end (72.1) connected to the first transverse wall (66) around the through-orifice (70) as well as a second end (72.2) distant from the first transverse wall (66), the conduit (72) comprising an internal diameter substantially equal to that of the through-orifice (70).

5. Sound absorption structure according to the preceding claim, characterized in that the tubular wall (64) has an internal cross-section and in that the conduit (72) and the through-orifice (70) have a passage section less than or equal to 25% of the internal cross-section of the tubular wall (64).

6. Acoustic absorption structure according to one of claims 2 to 5, characterized in that each cell (60) is delimited by several partitions (58) and in that the partitioning enclosure (62) is connected to at most two partitions (58) delimiting the cell (60).

7. Sound absorption structure according to the preceding claim, characterized in that the tubular wall (64) comprises at least one flat (78) configured to be pressed against a partition (58) of the cellular structure (52) and connected to the latter.

8. Sound absorption structure according to the preceding claim, characterized in that the tubular wall (64) has a constant external cross-section between the first and second transverse walls (66, 68) and comprises a curved main part (80) which has a cross-section approximately in the shape of an arc of a circle, a main flat (78) as well as two secondary flats (82.1, 82.2) positioned on either side of the main flat (78), connecting the latter to the curved main part (80).

9. Sound absorption structure according to the preceding claim, characterized in that the cells (60) each have a hexagonal section inscribed in a circle of cell diameter (D60) and in that the curved main part (80) and the two secondary flats (82.1, 82.2) are spaced from the partitions (58) of the cell (60) with a spacing between 5 and 50% of the cell diameter (D60).

10. Acoustic absorption structure according to one of claims 2 to 9, characterized in that the first and second transverse walls (66, 68) are oriented respectively towards the reflective layer (56) and the acoustically resistive layer (54).

11. Acoustic absorption structure according to one of claims 2 to 9, characterized in that the first and second transverse walls (66, 68) are oriented respectively towards the acoustically resistive layer (54) and the reflective layer (56).

12. Aircraft comprising at least one acoustic absorption structure according to one of the preceding claims.