Acoustic insulation device for an aircraft

Abstract

The invention relates to a sound insulation device, comprising at least one cavity (9), referred to as a quarter-wave cavity, a first joining of two walls (4-1, 5-1), respectively of the first strip (4) and the second strip (5), in contact with each other, such that a passage (10) is provided between said cavity (9) and another cavity (8), said other cavity (8), called a Helmholtz cavity, closed by a closing edge, a second joining of two walls (4-2, 5-2), respectively of the first strip (4) and the second strip (5), in contact with each other, each of the walls (4-1, 5-1; 4-2, 5-2) of said first and second joinings comprising a portion disposed along said closing edge of the Helmholtz cavity (8), referred to as a sacrificial portion and forming the end of the lining (1). Abstract figure: Figure 4

Description

Title of the invention: Acoustic insulation device for an aircraft. Technical field

[0001] The present invention relates to the field of acoustic insulation structures. It relates in particular to an acoustic insulation coating with a honeycomb structure. The coating of the invention may have applications, particularly in the aeronautical field, for example in aircraft propulsion unit nacelles. Previous technique

[0002] Coatings or panels with a honeycomb structure made up of cells or alveoli, i.e., juxtaposed hollow unit volumes, are used in many technical fields, particularly in aeronautics. They can exhibit high rigidity for a low mass. Coatings with a honeycomb structure having cells open on one face, or at least cells communicating with the outside of the panel, are used for their sound insulation properties. Such panels are sometimes called acoustic panels.

[0003] Honeycomb panels or cladding can be made of various materials, for example, plastics, composites, or metals. The cells can have various geometries. A well-known type of honeycomb structure has cells in the shape of right prisms with a hexagonal base. This type of hexagonal cell structure is often referred to as a "honeycomb" structure, but this expression is also used, somewhat loosely, to refer to honeycomb panels with other cell shapes.

[0004] Thus, a conventional acoustic panel or covering generally comprises a honeycomb core interposed between a perforated sheet or one comprising a metallic fabric permeable to acoustic waves forming a first face and a closing sheet, generally solid, sealing the cells and forming a second face of the covering.

[0005] The cells of acoustic panels act as small resonators, allowing the absorption of sound waves over a given frequency range. For a resonator to be effective, its absorption frequency range must include the frequency to which the panel is subjected. However, the relatively small cavities of acoustic panels correspond to high frequencies. It is therefore difficult to obtain an efficient honeycomb panel for certain applications subject to low frequencies.

[0006] For example, the propulsion systems of commercial aircraft comprise a turbomachinery engine and a nacelle that may include acoustic cladding to attenuate the noise generated during engine operation. However, the acoustic frequencies generated by an aircraft engine are relatively low and extend over a fairly wide range. The low frequencies that need to be attenuated are, for example, those below 2000 Hz, depending on the engine in question. The adoption of large-diameter propulsion systems tends to lower the frequencies of the acoustic waves they generate even further, particularly below 1000 Hz. However, the need for large-volume cells to absorb low frequencies leads to thick panels, which are not well-suited to an aeronautical application.

[0007] The object of the invention is to remedy at least partially these drawbacks. Summary

[0008] To this end, an acoustic insulation device is proposed, particularly for an aircraft, comprising a first perforated sheet, called the open sheet, permeable to acoustic waves, a second sheet, called the closing sheet, and an acoustic insulation coating disposed between said first and second sheets, the coating being formed by joining several honeycomb structures in a transverse direction, each of said honeycomb structures being formed by joining in the transverse direction a first longitudinal strip and a second longitudinal strip, the first and second strips forming a honeycomb structure being configured such that said honeycomb structure has, in a longitudinal direction orthogonal to the transverse direction: at least one cavity,open at the level of the first sheet and whose section gradually narrows between the first and second sheets until the closure of said cavity, called the quarter-wave cavity, a first joining of two walls, respectively of the first band and the second band, in contact with each other, so that a passage is provided between said cavity and another cavity, said other cavity, called the Helmholtz cavity, which has a progressively increasing cross-section between the first and second sheets and which is closed at the level of the first and second sheets by a closing edge, and a second joining of two walls, respectively of the first and second bands, in contact with each other, each of the walls of said first and second joinings comprising a portion disposed along said closing edge of the Helmholtz cavity, called the sacrificial portion.

[0009] Thus, the device according to the present invention allows for efficient acoustic treatment of low frequencies, while having good structural qualities and being able to be produced industrially, the sacrificial portion in particular avoiding piercing the Helmholtz cavity when the first sheet is pierced to make it permeable to acoustic waves.

[0010] According to another aspect, the sacrificial portion has a height in a direction, called vertical, orthogonal to the longitudinal and transverse directions, of between 1% and 30% of the height in the vertical direction of the coating, preferably between 5% and 25%. According to another aspect, each sacrificial portion extends along the longitudinal and vertical directions.

[0011] According to another aspect, at least one alveolar structure has a pattern that repeats along at least one of the longitudinal or transverse directions.

[0012] According to another aspect, the motif comprises a succession of a set of a quarter-wave cavity and a Helmholtz cavity.

[0013] According to another aspect, the motif comprises a succession of a set of two quarter-wave cavities and a Helmholtz cavity.

[0014] According to another aspect, the motif comprises a succession of a set of two Helmholtz cavities and a quarter-wave cavity.

[0015] According to another aspect, at least one of the alveolar structures includes at least one water drainage conduit away from the coating.

[0016] According to another aspect, at least one of the honeycomb structures includes at least two water drainage channels out of the coating, each of the channels being at a given, distinct height along the vertical direction.

[0017] According to another aspect, the device comprises, between a Helmholtz cavity and a quarter-wave cavity, at least one cavity, called an intermediate cavity, which is closed.

[0018] The invention also relates to a nacelle for an aircraft engine, comprising a sound insulation device as described above.

[0019] The invention also relates to an aircraft comprising a sound insulation device as described above. Brief description of the drawings

[0020] Other features, details and advantages will become apparent from reading the detailed description below and from analyzing the accompanying drawings, in which: Fig. 1

[0021] [Fig.1] represents, according to a schematic three-dimensional view, an acoustic coating conforming to the state of the art. Fig. 2

[0022] [Fig.2] represents, according to a schematic three-dimensional view, elements constituents of the coating of the [Fig. 1]. Fig. 3

[0023] [Fig.3] represents, according to a schematic three-dimensional view, the elements of the [Fig.2] after assembly. Fig. 4

[0024] [Fig.4] is a schematic perspective view of a detail of a coating acoustic insulation of a soundproofing device according to a first embodiment of the invention. Fig. 5

[0025] [Fig.5] is a schematic front view of the detail of [Fig.4]. Fig. 6

[0026] [Fig.6] is a schematic side view of the detail of [Fig.4]. Fig. 7

[0027] [Fig.7] is a schematic perspective view of a detail of a coating acoustic insulation of a soundproofing device according to a second embodiment of the invention. Fig. 8

[0028] [Fig.8] is a schematic front view of the detail of [Fig.7]. Fig. 9

[0029] [Fig.9] is a schematic side view of the detail of [Fig.7]. Fig. 10

[0030] [Fig. 10] is a schematic perspective view of a detail of a coating acoustic insulation of a soundproofing device according to a third embodiment of the invention. Fig. 11

[0031] [Fig.11] is another schematic perspective view of the detail of [Fig.10]. Fig. 12

[0032] [Fig. 12] is a schematic front view of the detail of [Fig. 10]. Fig. 13

[0033] [Fig. 13] is a perspective view of the detail of [Fig. 10] according to a variant of realization. Fig. 14

[0034] [Fig. 14] schematically represents, in cross-section, a propulsion unit of an aircraft whose nacelle is equipped with a soundproofing device according to the present invention. Description of the implementation methods

[0035] The examples and associated conditions detailed herein are primarily intended to help the reader understand the principles of the present invention and not to limit its scope to these specific examples and conditions. It will be understood that a person skilled in the art can conceive of various arrangements which, although not explicitly described or illustrated herein, nevertheless embody the principles of the present invention and are included in its spirit and scope.

[0036] Furthermore, to facilitate understanding, the following description may describe relatively simplified implementations of the present invention. As a person skilled in the art will understand, other implementations of the present invention may be of greater complexity.

[0037] In some cases, examples of modifications to the present invention may also be shown. This is done simply to aid understanding and, again, not to define the scope or establish the limits of the present invention. These modifications are not an exhaustive list, and a person skilled in the art may make other modifications while remaining within the scope of the present invention.

[0038] Furthermore, all the following statements relating to the principles, aspects and implementations of the present invention, as well as specific examples thereof, are intended to encompass both the structural and functional equivalents thereof, whether currently known or developed in the future.

[0039] Figure 1 schematically represents a sound insulation device comprising a sound-absorbing coating, known in the prior art. It comprises cells (or cavities) A1, A2, A3, etc., juxtaposed to one another in two directions orthogonal to each other so as to form a honeycomb structure. A first direction D1 of cell juxtaposition is called longitudinal, and a second direction D2 of cell juxtaposition, orthogonal to the first direction D1, is called transverse. A third direction D3, in which the thickness of the panel extends, is defined orthogonally to the first direction D1 and to the second direction D2. The third direction D3 can be conventionally called the vertical direction D3 (without prejudice to the orientation of the sound-absorbing coating).

[0040] As can be seen from [Fig. 1], on one face of the coating, the AL...A3 cells are open. A perforated sheet 2 covers them, forming a resistive surface allowing communication between the Al...A3 cells and the external environment, so that the first face is said to be open. The sheet 2 is called the opening sheet.

[0041] On a second face, the cells Al...A4 are closed by a closing sheet, 3, for example a solid sheet, obstructing the bottom of the cells.

[0042] In the prior art, as in the invention, the closing sheet is generally a solid sheet. However, it may also be a sheet with holes. Indeed, a solid sheet is used for simple acoustic treatments, known as SDOF (Single Degree of Freedom), and forms a reflective backing with respect to acoustic waves. A closing sheet with holes is used for acoustic treatments known as DDOF (Double Degree of Freedom), for which a stack of two layers of honeycomb structure is used, the layers being separated by an intermediate porous skin formed by said closing sheet.

[0043] Although not excluded, the stacking of two honeycomb structures such as those formed in the invention, and examples of which are described below with reference to the following figures, is of generally limited interest, because such a stacking of structures generally leads to a thick acoustic coating, whereas the structure developed in the invention makes it possible to limit the thickness of the structure compared to known structures allowing the treatment of similar acoustic frequencies.

[0044] In [Fig.1], the cells of the alveolar structure shown here are said to be hexagonal, in that their volume is that of a right prism with a hexagonal base extending between the first face and the second face of the soundproofing coating.

[0045] The hexagonal cells are arranged in a staggered pattern, with a longitudinal offset allowing them to interlock without dead volume.

[0046] Fig.2 represents two bands for forming the cellular structure of the coating of Fig.1, according to a technique known in the prior art on which the present invention is based.

[0047] In particular, a first band 4 has a corrugation formed by successive regular folds. Each corrugation forms half of a hexagonal cell. A second band 5 is identical to the first band 4.

[0048] The first band 4 and the second band 5 are joined to each other, so as to form a structure having a longitudinal succession of hexagonal cells A1, A2; between which walls 6 are in contact and linked together, for example by gluing or welding. By joining and fixing transversely (along the second direction D2) to the structure of [Fig. 3] another identical structure, and so on, the cellular structure of the coating of [Fig. 1] is obtained.

[0049] An acoustic insulation device D (also called a soundproofing device D) according to the present invention is now described, in particular for an aircraft engine nacelle, with reference to Figures 4 and following.

[0050] As can be seen from [Fig. 1], the device D comprises a sound-insulating coating, referred to as 1 in the figures. The device D also comprises a first sheet 2, called the opening sheet, and a second sheet 3, called the closing sheet, preferably solid, the coating 1 extending between the first and second sheets 2, 3, as already described in relation to Figures 1 to 3. The ends of the coating 1 in the plane (D1, D2) are called the first face and the second face. The first face opens onto the first sheet 2 and the second face opens onto the second sheet 3.

[0051] The invention is now described in relation to figures 4, 5 and 6.

[0052] Figure 4 represents elements, namely pairs of bands 4 and 5, constituting of the acoustic insulation coating 1. More specifically, [Fig.4] represents a small longitudinal portion (along the longitudinal direction) of the strips joined and fixed to each other transversely (along the transverse direction D2).

[0053] Each of the bands 4, 5 extends essentially along a plane P4, P5 itself extending along the longitudinal direction D1 and the vertical direction D3.

[0054] Each pair of bands 4 and 5 forms a first alveolar structure 11.

[0055] Each of the strips exhibits deformations, respectively in a single transverse direction. The deformations thus form hollows with respect to their respective planes.

[0056] According to their simplest form, each strip is metallic and shaped by a forming technique. Possible forming techniques include, for example, deep drawing and hydroforming.

[0057] Band 4 is described in detail.

[0058] As can be seen in Figures 4 to 6, the first band 4 comprises a succession of a set of motifs M which are repeated along the longitudinal direction DL. Each motif M comprises a first portion 4-1, and a second portion 4-2 arranged on either side of a first half-cavity 4-3. Each motif M also comprises a second half-cavity 4-4.

[0059] We speak of half-cavities 4-3, 4-4 because the assembly of the band 4 to the band 5 forms "complete" cavities by juxtaposing the half-cavities 4-3, 4-4 with half-cavities of the band 5, as will be detailed later.

[0060] The first portion 4-1 comprises a wall 4-5, extending substantially in the plane P4, and extended by a half-passage 4-6 formed between the first half-cavity 4-3 and the second half-cavity 4-4 of the preceding motif M1. The half-passage 4-6 comprises a hemisphere integral with the rectangular wall 4-5.

[0061] The wall 4-5 has a general L-shape comprising essentially two rectangular parts around the first half-cavity 4-3. A first wall, called sacrificial half-wall, 4-5s, extends over a closing edge of the first half-cavity 4-3, forming an end (along the direction D3) of the coating 1, while a second wall, 4-5v, extends mainly along the direction D3.

[0062] The second portion 4-2 comprises a wall 4-7 extending substantially in the plane P4, and extended by a half-passage 4-8 formed between the first half-cavity 4-3 and the second half-cavity 4-4 of the motif M. The half-passage 4-8 comprises a hemisphere integral with the rectangular wall 4-5.

[0063] The wall 4-7 comprises two rectangular parts forming an L around the first half-cavity 4-3. A first wall, called the sacrificial half-wall, 4-7s, extends over a closing edge of the first half-cavity 4-3, forming the end (along the direction D3) of the coating 1, while a second wall, 4-7v, extends mainly along the direction D3.

[0064] The sacrificial half-wall 4-7s extends in line with the sacrificial half-wall 4-5s. The entire sacrificial half-wall 4-5s, 4-7s constitute a sacrificial wall 4-s of the pattern M of the strip 4. The dimension in the D3 direction of the sacrificial portion 4-s is advantageously between 0.1 mm and 1 cm, preferably between 0.5 mm and 3 mm. In other words, the sacrificial portion has a height (along D3) between 1% and 30% of the height (along D3) of the coating 1, preferably a height between 5% and 25% of the height (along D3) of the coating 1.

[0065] In Figures 4 to 6, the first half-cavity 4-3 is delimited by a trapezoid T4-3, a smaller base b4-3 and a larger base B4-3 of which extend along the direction DI. In Figures 4 to 6, the larger base B4-3 of motif M is positioned above the smaller base b4-3. Two substantially triangular walls 4-9, 4-10, in a plane (D2, D3), connect one end of the larger base B4-3 to one end of the smaller base b4-3 and, respectively, to the first portion 4-1 and the second portion 4-2.

[0066] In Figures 4 to 6, the second half-cavity 4-4 is delimited by a trapezoid T4-4, a small base b4-4 and a large base B4-4 of which extend along the direction DI. In Figures 4 to 6, the small base b4-4 of motif M is positioned above the large base B4-3. Two substantially triangular walls, 4-11, 4-12, in a plane (D2, D3), connect one end of the large base B4-4 to one end of the small base b4-4 and, respectively, to the second portion 4-2 and the first portion 4-1 of the following motif M+1.

[0067] In the example shown here, the first band 4 and the second band 5 are of similar shapes, mirroring each other, so that they are symmetrical to each other, when joined together, with respect to their joining plane.

[0068] The first strip 4 and the second strip 5 are joined and assembled, namely that the plane P4 is brought into contact with the plane P5. The strips are fixed together, for example by gluing or welding their contact areas, in particular between their respective first portions 4-1,5-1 and between their respective second portions 4-2, 5-2. The first half-cavity 4-3 of the first band 4 is placed opposite the first half-cavity 5-3 of the second band 5, thus forming a first cavity 8. The large bases B4-3 and B5-3 are brought into contact with each other and form the closing edge of the cavity 8. The second half-cavity 4-4 of the first band 4 is placed opposite the second half-cavity 5-4 of the second band 5, thus forming a second cavity 9. The small bases b4-4, b5-4 are brought into contact with each other and form the bottom of the coating 1 (in the horizontal position of the aircraft).The half-passages of the first band 4 are placed opposite the second half-passages of the second band 5, thus forming a passage 10 between the first cavity 8 and the second cavity 9. .

[0069] The sacrificial walls 4-s, 5-s are also brought into contact when the bands 4 and 5 are placed side by side.

[0070] In other words, when the bands 4 and 5 are joined together, the wall 4-1 is in contact with the wall 5-1 (forming a first joining) on ​​one side and, on the other side, the wall 4-2 is in contact with the wall 5-2 (forming a second joining), each of the first and second joinings comprising a sacrificial portion, respectively 4-5s, 5-5s; 4-7s, 5-7s.

[0071] The assembly of the first strip 4 with the second strip 5 thus forms a three-dimensional structure 11, extending essentially along the longitudinal direction Dl, and represented in figures 4 to 6.

[0072] As can be seen from the figures, the second cavity 9 is open on one face in a plane (D1, D2), this face corresponding to the first face 2 of the coating 1. The opening of the second cavity 2 has a hexagonal cross-section. The cross-section of the first cavity 9 gradually narrows towards the bottom F of the second cavity 9. In the example shown here, the cross-section narrows until it becomes zero and takes the form of a straight line at the junction of the first strip 4 with the second strip 5 forming the bottom of the second cavity 9, at the midpoint of a median of the hexagon formed by the opening of the second cavity 9. The bottom can be located at the level of the second sheet 3, as in the example shown here, or between the first face 2 and the second face 3.Thus, in the example shown here, at the bottom level, that is to say at the level of the second face 3 of the soundproofing coating once the latter has been formed (with the exception of the closing sheet, of thin thickness, namely here a solid sheet, closing said second face 3), the first strip 4 is in contact with the second strip 5. .

[0073] As can also be seen from the figures, the first cavity 8, which advantageously extends over the entire height (dimensions along the third direction D3) of the structure 11, will be closed once the coating is formed at both the first face 2 and the second face 3. Indeed, the second cavity 8 has an identical shape to the second cavity 9, but with an opposite orientation along the third direction D3. Thus, at or near the first face, the first strip 4 is in contact with the second strip 5, which closes said first cavity 8 at said first face 2 of the coating 1. In particular, the contact between the first strip 4 and the second strip 5 can take the form of a straight line perpendicular to a median of the hexagon formed by the cross-section of the first cavity 8 at the second face 3.Thus, at the level of the second face 3, where the first cavity 8 of the structure 11 is open according to a hexagonal section, said first cavity 8 is closed once the coating constituted by the closure sheet forming the second face 3. .

[0074] The configuration shown here maximizes the height of the second cavities 9, while maximizing the volume of the first cavities 8 (which allows for the processing of lower frequencies than with smaller cavities), without any loss of acoustic surface area. It does not exhibit any breaks in slope in the height of the walls, which would lead to a solution that would be difficult to manufacture.

[0075] It is noted that each second cavity 9 forms a quarter-wave resonator. The assembly comprising the passage 10 and the cavity 8 forms a Helmholtz resonator whose throat is formed by the passage 10. The quarter-wave resonator and the Helmholtz resonator are therefore coupled in series at the entrance of the passage 10. Hereafter, the cavities 8 are called "Helmholtz cavities" and the cavities 9 "quarter-wave cavities".

[0076] As can be seen from the figures, the coating 1 comprises two transversely adjacent structures 11 mounted in a staggered arrangement, that is to say, each first cavity 8 of a structure 11 is adjacent, in the transverse direction D2, to two second cavities 9 of neighboring structures, and each second cavity 9 of a structure 11 is adjacent, in the transverse direction D2, to two first cavities 8 of neighboring structures. In other words, staggered does not mean alternation or succession but an offset over two rows.

[0077] Such a staggered configuration can be obtained by alternating the arrangement of structures 11 rotated 180° relative to their neighbors, or by assembling them with a longitudinal offset of every other structure 11. However, the solution using a longitudinal offset presents the technical difficulty that the structures exhibit after assembly of the offset longitudinal ends, which necessitates special treatment of the longitudinal edges of the cladding (cutting, or filling this offset, etc.).

[0078] Due to the respective section restrictions of the first cavities 8 and the second cavities 9, said first cavities 8 and second cavities 9 are interlocked with each other transversely, so that the walls limiting said first cavities and second cavities in the transverse direction D2 come into contact with each other.

[0079] It is noteworthy that the joining of two structures 11 further forms intermediate cavities 12. The intermediate cavities 12 are located in longitudinal intervals between the first and second cavities of two transversely adjacent structures 11. The intermediate cavities 12 have a substantially parallelogram-shaped cross-section at the first face 1. The intermediate cavities 12 extend transversely between the walls 4-2, 4-11, 5-2, 5-11 of the first and second strips joined together to form the structures 11. The intermediate cavities 12 are closed at the second face 3 by the closing sheet installed at said second face 3 of the soundproofing covering.The cross-section of the intermediate cavities 12 evolves within the thickness of the soundproofing coating (in the third direction D3), because this cross-section depends on the cross-sections of the Helmholtz cavities 8 and quarter-wave cavities 9 delimited around the intermediate cavity 12.

[0080] The formation of a honeycomb structure of soundproofing coating by joining structures of complementary geometries, allowing them to interlock by forming the desired cavities between them, also makes it possible to avoid the joining of multiple walls in the honeycomb structure, which optimizes the mass of the coating.

[0081] It is noted that the second cavities 9 and the intermediate cavities 12 open onto the first face 1 in a regular and perfectly interlocking manner. It is also noteworthy that the first cavities 8, with their hexagonal openings, and the intermediate cavities 12, with their parallelogram-shaped openings, open onto the second face 3.

[0082] The intermediate cavities 12 form resonators capable of processing different (a priori higher) acoustic frequency ranges than those processed by the first and second cavities forming the coupling of the Helmholtz and quarter-wave resonators.

[0083] Thus, the acoustic coating has an alveolar structure with three types and dimensions of cavities, which allows a very wide frequency range to be treated compared to a coating with a single cell geometry.

[0084] The honeycomb structure obtained by transversely joining structures 11, themselves obtained by transversely joining shaped strips 4, 5, is thus relatively simple to produce and implement. Furthermore, it is possible to impart a curvature, particularly a transverse one, to this honeycomb structure.

[0085] As already indicated, the soundproofing device D is obtained by adding a closing sheet, typically a solid sheet, to one of the surfaces of the honeycomb structure, thus forming a closed face, and a resistive sheet (for example a metal or carbon sheet with multiple perforations or a sheet comprising a metallic fabric permeable to acoustic waves) to the other face which thus remains open.

[0086] It should be noted that the sacrificial walls 4-s, 5-s ensure that, during the drilling of the aperture sheet 2, no Helmholtz cavities 8 are breached, which would render them ineffective for absorbing acoustic waves. Thus, it is possible that the walls 4-s, 5-s may be affected during drilling, but their height (in the direction D3) ensures that the Helmholtz cavities themselves remain intact.

[0087] As can be seen particularly in [Fig. 6], the device D also includes drainage channels. These are the passages 10 (formed by two half-passages in each of the bands 4, 5) which extend along the entire length of the alveolar structure 11.

[0088] The drainage channels 10 thus allow the evacuation of water which could penetrate or form by condensation in the alveolar structure of the coating.

[0089] In other words, drainage consists of connecting the cavities to each other by means of small-section passages allowing the water present in the structure to flow by gravity to one or more drainage points. In the illustrated embodiments, the passages 10 (formed by two half-passages in each of the strips 4, 5) extend along the entire length of the alveolar structure 11, that is to say, not only between the cavities 8, 9 but also in the intermediate cavities 12.

[0090] With regard to the first and second cavities 8, 9, drainage must be provided at the level of the second face 3, which is closed. To this end, in addition to the passage 10 formed between a first cavity 8 and an adjacent second cavity 9, a similar or smaller passage 10 is formed (by a half-passage formed in the second band 5 and a corresponding half-passage formed in the first band 4) to the other adjacent second cavity 8. Thus, in a structure 11, water can flow along the entire length of the structure between the first and second cavities, at the level of the second face 3, until the lining is typically drained away at a low point on it.

[0091] Regarding the intermediate cavities, closed at the level of the second surface, they are connected to each other by a drain, for example a longitudinal notch, formed at the level of the second face 3.

[0092] As can be seen from figures 4 to 6, the passages 10 are arranged at the level of the bottom of the coating 1, which simplifies the evacuation of water.

[0093] The second embodiment of the invention is now described, in relation to figures 7, 8, and 9.

[0094] The soundproofing device D according to this second embodiment is identical to the soundproofing device D according to the first embodiment, except that it includes an additional level of drainage ducts 10'.

[0095] As can be seen from figures 7 to 9, the passages 10' extend in the coating 1 into the cavities 8, 9 and 12, and into the vertical walls 4-5v, 4-7v, substantially halfway up the trapezoids and the vertical walls 4-5v (5-5v) and 4-7v (5-7v).

[0096] The passages 10' extend parallel to the passages 10 in figures 7 to 9.

[0097] This embodiment allows for more efficient drainage of condensate, since it allows the water evacuation flow rate to be doubled, and also allows the water to be evacuated more easily, depending on the position of the aircraft.

[0098] It is noted that the height of the passages 10' can vary, according to constraints of propagation of acoustic waves in the coating 1 and / or according to manufacturing constraints.

[0099] It is also noted that the passages 10' can be inclined, or even convergent, with the passages 10, depending on the path that we want the water to take in the coating 1.

[0100] It is noted that, as an alternative, passages 10' can be substituted for passages 10.

[0101] The embodiment of figures 7 to 9 is not described further and reference will be made to the description of the first embodiment for more details.

[0102] The third embodiment is now described, with reference to Figures 10, 11 and 12.

[0103] This embodiment is similar to the first two embodiments described, in that the soundproofing device D comprises a succession of quarter-wave cavities 8, Helmholtz 9 and intermediate 12. The device D also includes sacrificial portions associated with each Helmholtz cavity 8. The device D also includes drainage passages 10 located at the bottom of the coating 1.

[0104] The soundproofing device D according to this third embodiment differs from the two previous embodiments by the reasons M.

[0105] As can be seen in Figures 10 to 12, a first pair of bands 4, 5, comprises, on either side of each Helmholtz cavity 8, two successive quarter-wave cavities 9. In the detail of [Fig. 10], one observes successively two quarter-wave cavities 9, then a Helmholtz cavity 8, then two quarter-wave cavities 9.

[0106] A second pair of bands 4', 5' comprises, on either side of each quarter-wave cavity 9, two successive Helmholtz cavities 8. In the detail of [Fig. 10], one observes successively two Helmholtz cavities 8, then a quarter-wave cavity 9, then two Helmholtz cavities 8.

[0107] This succession of several Helmholtz cavities 9 makes it possible to broaden the bandwidth of the frequencies acoustically treated by the device D and to center the bandwidth at lower frequencies, for example from 1000 Hz to 3000 Hz.

[0108] According to this embodiment, the intermediate cavities 12 between a Helmholtz cavity 8 and a quarter-wave cavity 9 are hexagonal, as already described in relation to the first two embodiments. The intermediate cavities 12 between two Helmholtz cavities 8 or two quarter-wave cavities have a different shape, with a cross-section delimited by a U-shaped edge and a straight edge, in a plane orthogonal to the contact plane P4, P5.

[0109] As is already apparent from the preceding description, for each of the illustrated embodiments, the sacrificial walls guarantee the integrity of the Helmholtz cavities, which makes the soundproofing device D particularly effective.

[0110] In [Fig. 12], drilling holes O in sheet 2 are shown to illustrate that the cavities 8 remain intact after this step.

[0111] Moreover, according to the patterns of the three embodiments, it is possible to choose the frequencies to be absorbed preferentially.

[0112] It is added that passages 10, 10' ensure rapid evacuation of any condensate which could damage device D.

[0113] The invention is now described with reference to [Fig.13].

[0114] As can be seen from this figure, this is a variant of the embodiment already described in relation to figures 10 to 12.

[0115] According to this embodiment, at least one intermediate cavity, referenced 12b, is closed, for example by bonding. Preferably, the intermediate cavities 12b are regularly distributed in the coating 1. For example, a row (along direction D2, for example) of intermediate cavities is closed at a given frequency. In [Fig. 13], the frequency is one row out of three. The invention is not limited to this frequency, and a frequency between one row out of ten and one row out of two, advantageously one row out of three or one row out of four, can be considered. Along direction D1, there is an alternation of two open cavities and one closed cavity in Figures 10 to 12.

[0116] Alternatively, the intermediate cavities 12b are distributed irregularly in the coating 1.

[0117] Alternatively, the intermediate cavities are filled with material.

[0118] Blocking certain intermediate cavities makes it possible to further widen the bandwidth of the frequencies acoustically treated by the device D and to center the bandwidth at lower frequencies, for example from 500 Hz to 3500 Hz.

[0119] The invention finds a preferential application in the formation of a sound-absorbing panel for the nacelle of an aircraft propulsion unit. A propulsion unit The aircraft is schematically represented in cross-section in [Fig. 14]. It comprises an engine 15 with a turbomachine equipped with a fan 16, which is installed in a nacelle 17. The cladding 18 can be installed in various locations particularly exposed to acoustic waves, in the nacelle and more generally in the propulsion unit. The sound-absorbing cladding 18, according to one embodiment of the invention, can be installed so as to form, at least in part, the inner face of the front part of the aircraft propulsion unit nacelle. The cladding 18 can be installed in a mid-area of ​​the inner face of the nacelle, behind the fan 16. The cladding 18 can also be installed on an inner face of the rear part of the nacelle. The cladding 18 can also be installed on a casing of the engine 15.

[0120] The invention thus developed offers an acoustic coating suitable for treating low frequencies compared to coatings of the same thickness known in the prior art. In addition, thanks to the presence of cavities of three different sizes and shapes, namely first and second cavities communicating with each other to form Helmholtz resonators for treating low frequencies and intermediate cavities for treating higher frequencies, the frequency range treated by the coating is not only shifted compared to a conventional acoustic panel, but also broadened.

[0121] Forming the coating, particularly its honeycomb structure, using structures with complementary geometries avoids the bonding of multiple walls, thus optimizing the coating's mass. This coating can be obtained through conventional industrial forming processes that ensure the resonator cavities are not damaged. It is easy to implement. Drainage of water present in the honeycomb structure can be readily managed. The invention is compatible with the formation of a curved sound-absorbing coating. The coating thus finds a preferred application in aircraft propulsion unit nacelles, the surfaces of which have one or two radii of curvature.

[0122] Modifications and improvements to the above-described implementations of the present invention may be apparent to those skilled in the art. In particular, the described embodiments may be combined as long as they are not incompatible. The above description is illustrative by way of examples rather than exhaustive. The scope of the present invention is therefore limited only by the scope of the claims below.

Claims

Demands

1. Acoustic insulation device, particularly for an aircraft, comprising a first sheet (2), perforated with holes, referred to as the opening sheet, permeable to acoustic waves, a second sheet (3), referred to as the closing sheet, and an acoustic insulation coating (1) disposed between said first sheet (2) and second sheet (3), the coating (1) being formed by joining along a direction referred to as the transverse direction (D2) several honeycomb structures (11), each of said honeycomb structures (11) being formed by joining in the transverse direction (D2) a first longitudinal strip (4) and a second longitudinal strip (5), the first strip (4) and the second strip (5) forming a honeycomb structure (11) being configured such that said honeycomb structure (11) has in a longitudinal direction (D1), orthogonal to the transverse direction: at least one cavity (9),open at the level of the first sheet (2) and whose cross-section gradually narrows between the first sheet (2) and the second sheet (3) until the closure of said cavity (9), called the quarter-wave cavity, a first joining of two walls (4-1, 5-1), respectively of the first band (4) and the second band (5), in contact with each other, a passage (10) being provided between said cavity (9) and another cavity (8), said other cavity (8), called the Helmholtz cavity, which has a progressively increasing cross-section between the first sheet (2) and the second sheet (3) and which is closed at the level of the first sheet (2) by a closing edge, a second joining of two walls (4-2, 5-2), respectively of the first band (4) and the second band (5), in contact with each other, each of the walls (4-1, 5-1; 4-2, 5-2) of said first and second adhesions comprising a portion disposed along said closing edge of the Helmholtz cavity (8),said sacrificial portion and forming the end of the coating (1).

2. Device according to claim 1, wherein the sacrificial portion has a height in a direction, called vertical (D3), orthogonal to the longitudinal direction (D1) and to the transverse direction (D2), of between 1% and 30% of the height in the vertical direction (D3) of the coating (1), preferably of between 5% and 25%.

3. Device according to any one of the preceding claims, wherein each sacrificial portion extends along the longitudinal direction (D1) and the vertical direction (D3).

4. Device according to any one of the preceding claims, wherein at least one alveolar structure has a pattern that repeats along at least one of the longitudinal (D1) or transverse (D2) directions.

5. Device according to the preceding claim, wherein the motif comprises a succession of a set of a quarter-wave cavity and a Helmholtz cavity.

6. Device according to any one of the preceding claims, wherein the motif comprises a succession of a set of two quarter-wave cavities and a Helmholtz cavity.

7. Device according to any one of the preceding claims, wherein the motif comprises a succession of a set of two Helmholtz cavities and a quarter-wave cavity.

8. Device according to any one of the preceding claims, wherein at least one of the honeycomb structures (11) comprises at least one water drainage conduit away from the coating (1).

9. Device according to the preceding claim, wherein at least one of the honeycomb structures (11) comprises at least two water drainage conduits out of the coating (1), each of the conduits being at a given, distinct height along the vertical direction (D3).

10. Device according to any one of the preceding claims, comprising between a Helmholtz cavity and a quarter-wave cavity at least one cavity, called an intermediate cavity, which is closed.

11. Nacelle for an aircraft engine, comprising a sound insulation device according to any one of the preceding claims.

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