ACOUSTIC PANEL WITH AT LEAST TWO HONEYCOMB STRUCTURES NESTED INSIDE ONE ANOTHER, AIRCRAFT WITH AT LEAST ONE SUCH ACOUSTIC PANEL

Description

[0001] The present application relates to an acoustic panel comprising at least two cellular structures nested within each other and to an aircraft comprising at least one such acoustic panel.

[0002] According to one embodiment, an acoustic panel comprises first and second superimposed alveolar structures, positioned between a reflective layer (impermeable to acoustic waves) and a first acoustically resistive layer (porous to acoustic waves) in contact with an external environment in which acoustic waves propagate, a second porous acoustically resistive layer being interposed between the first and second alveolar structures.

[0003] According to one configuration, the first and second honeycomb structures are in the form of plates which comprise planar faces oriented towards each other.

[0004] Given this geometry, it is difficult to correctly position the first and second honeycomb structures relative to each other and maintain this position in order to obtain optimal operation of the acoustic treatment.

[0005] Document US 6,328,258 B1 describes an air intake structure for an aircraft engine, comprising an acoustic panel formed from two cellular materials arranged between two external layers.

[0006] Document US 2014 / 326536 A1 describes an acoustic panel comprising two adjacent honeycomb structures separated by a porous layer, and sandwiched between a porous layer and a reflective layer.

[0007] Document US 2010 / 148001 describes an aircraft cabin panel for sound absorption in an interior space, comprising two outer layers and a first honeycomb structure disposed between a recess of a second honeycomb structure.

[0008] The present invention aims to overcome all or part of the drawbacks of the prior art. To this end, the invention relates to an acoustic panel comprising a first longitudinal edge, a first acoustically resistive layer, a second reflective layer, at least first and second cellular structures interposed between the first and second layers and at least one third acoustically resistive layer interposed between the first and second cellular structures, the first acoustically resistive layer and the second reflective layer being joined at the first longitudinal edge.The first cellular structure has a first face, a second face opposite the first face and in contact with the second reflective layer as well as a first edge oriented towards the first longitudinal edge of the acoustic panel, the second cellular structure comprising a first face in contact with the first acoustically resistive layer and a second face opposite the first face as well as first and second edges connecting the first and second faces, the first edge of the second cellular structure being oriented towards the first longitudinal edge of the acoustic panel.

[0009] According to the invention, the first cellular structure comprises a step which extends from the first face towards the second face and forms a housing sized to house the second cellular structure and the third acoustically resistive layer, the second cellular structure being positioned in the housing so that the first faces of the first and second cellular structures are coplanar and in contact with the first acoustically resistive layer, the first edges of the first and second cellular structures are coplanar and the second edge of the second cellular structure is in contact with the step.

[0010] According to the invention, the first and second alveolar structures are nested within each other and correctly positioned relative to each other thanks to the offset, which contributes to optimizing the acoustic treatment.

[0011] According to another characteristic, the acoustic panel comprises at least one reinforcement inserted between the first acoustically resistive layer and the second reflective layer, between the first longitudinal edge of the acoustic panel and the first edges of the first and second cellular structures; the reinforcement having a first surface extending in a plane common to the first face of the second cellular structure, a second surface extending in a plane common to the second face of the first cellular structure, a third surface in contact with the first edges of the first and second cellular structures as well as a fourth inclined surface connecting the first and second surfaces.

[0012] According to another characteristic, the first surface has a transverse dimension greater than 1 cm and less than 5 cm.

[0013] According to another characteristic, the reinforcement is a honeycomb structure which has cells opening at the first and second surfaces of the reinforcement.

[0014] According to another characteristic, the cells of the reinforcement have a section smaller than that of the first and second alveolar structures.

[0015] According to another characteristic, the reinforcement cells have a width between 3 and 6 mm.

[0016] According to another feature, the second reflective layer comprises an extension which extends beyond the second surface of the reinforcement.

[0017] According to a first embodiment, the first layer extends continuously over the first and second honeycomb structures, the fourth surface of the reinforcement and the extension of the second reflective layer.

[0018] According to a second embodiment, the first layer comprises a first acoustically resistive part which extends over the first and second alveolar structures and at least partially over the first surface of the reinforcement as well as a second part which extends at least partially over the first surface of the reinforcement, over the fourth surface of the reinforcement and over the extension of the reflective layer, the first and second parts comprising an overlapping zone at right angles to the first surface of the reinforcement.

[0019] According to another characteristic, the first and second alveolar structures comprise alveoli having a width greater than or equal to 12.7 mm.

[0020] The invention also relates to an aircraft comprising at least one acoustic panel according to one of the preceding characteristics.

[0021] 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: There figure 1 is a cross-section of a portion of an acoustic panel illustrating one embodiment of the invention, The figure 2 is a cross-section of the different elements of the acoustic panel visible on the figure 1 , before its assembly, The figure 3 is a cross-section of an edge of an acoustic panel illustrating an embodiment of the invention, The figure 4 is a cross-section of a door of a thrust reverser of an aircraft illustrating an embodiment of the invention.

[0022] According to an embodiment visible on the figures 1 et 2 , an acoustic panel 10 comprises a first face 10.1 in contact with an environment in which acoustic waves propagate as well as a second face 10.2 opposite the first face 10.1. This acoustic panel 10 extends from a first longitudinal edge 12.1 to a second longitudinal edge 12.2.

[0023] According to one application, the acoustic panel 10 forms a door of a thrust reverser of a propulsion assembly of an aircraft. Of course, the invention is not limited to this application. Thus, the acoustic panel 10 can be used in different areas of an aircraft. Whatever the applications, an aircraft comprises at least one acoustic panel 10.

[0024] The acoustic panel 10 comprises at least first and second zones Z1, Z2. According to one configuration, the first zone Z1 is positioned between the first longitudinal edge 12.1 of the acoustic panel 10 and the second zone Z2. The second zone Z2 is positioned between the second longitudinal edge 12.2 of the acoustic panel 10 and the first zone Z1, the first and second zones Z1, Z2 being contiguous.

[0025] According to one embodiment, the acoustic panel 10 comprises a first acoustically resistive layer 14, porous to acoustic waves, which extends at least over the first and second zones Z1, Z2 and has an outer face 14.1 forming the first face 10.1 of the acoustic panel 10 as well as an inner face 14.2 opposite the outer face 14.1. The acoustic panel 10 also comprises a second reflective layer 16 which extends at least over the first and second zones Z1, Z2 and has an outer face 16.1 forming the second face 10.2 of the acoustic panel 10 as well as an inner face 16.2 opposite the outer face 16.1.

[0026] At the level of the second zone Z2, the acoustic panel 10 comprises, from the first face 10.1 of the acoustic panel 10, the first acoustically resistive layer 14, a first cellular structure 18 and the second reflective layer 16. At the level of this second zone Z2, the acoustic panel 10 comprises a single cellular structure 18. The first cellular structure 18 has a first face 18.1 in contact with the inner face 14.2 of the first acoustically resistive layer 14 as well as a second face 18.2 in contact with the inner face 16.2 of the second reflective layer 16.

[0027] At the level of the first zone Z1, the acoustic panel 10 comprises, from the first face 10.1, the first acoustically resistive layer 14, a second alveolar structure 20, at least one third acoustically resistive layer 22 (porous to acoustic waves), a third alveolar structure 24 and the second reflective layer 16.

[0028] The second alveolar structure 20 comprises a first face 20.1 in contact with the inner face 14.2 of the first acoustically resistive layer 14 as well as a second face 20.2 in contact with the third acoustically resistive layer 22. The second alveolar structure 20 has a thickness E20 corresponding to the distance separating the first and second faces 20.1, 20.2.

[0029] The second honeycomb structure 20 comprises a first edge 26.1 oriented towards the first longitudinal edge 12.1 of the acoustic panel 10 and a second edge 26.2 opposite the first edge 26.1, the first and second edges 26.1, 26.2 connecting the first and second faces 20.1, 20.2. The second honeycomb structure 20 has a transverse dimension L20 corresponding to the distance separating the first and second edges 26.1, 26.2.

[0030] According to a feature of the invention, the first and third alveolar structures 18, 24 form a single and same alveolar structure subsequently called the first alveolar structure 18. At the level of the first zone Z1, the second face 18.2 of the first alveolar structure 18 is also in contact with the reflective layer 18. This first alveolar structure 18 comprises a first edge 28.1 oriented towards the first longitudinal edge 12.1 of the acoustic panel 10.

[0031] This first alveolar structure 18 comprises a recess 30 which extends from the first face 18.1 towards the second face 18.2 and forms a housing 32 sized to house the second alveolar structure 20 and the third acoustically resistive layer 22.

[0032] Thus, the housing 32 has a first dimension, taken perpendicular to the first acoustically resistive layer 14, substantially equal to the sum of the thickness of the third acoustically resistive layer 22 and the thickness E20 of the second cellular structure 20 so that the first face 20.1 of the second cellular structure 20 is substantially coplanar with the first face 18.1 of the first cellular structure 18.

[0033] The housing 32 has a second dimension, taken parallel to the first acoustically resistive layer 14 and perpendicular to the first longitudinal edge 12.1 of the acoustic panel 10, substantially equal to the transverse dimension L20 of the second cellular structure 20 so that the first edges 26.1, 28.1 of the first and second cellular structures 18, 20 are substantially coplanar when the second edge 26.2 of the second cellular structure 20 is in contact with the recess 30.

[0034] According to the invention, the first and second alveolar structures 18, 20 are nested within each other and correctly positioned relative to each other thanks to the recess 30, which contributes to optimizing the acoustic treatment, the cells of the first alveolar structure 18 being substantially aligned with those of the second alveolar structure 20. According to one operating mode, the first alveolar structure 18 is machined by ultrasound to obtain the recess 30 and the housing 32.

[0035] According to one embodiment, each of the first and second cellular structures 18, 20 has cells with a large cross-section. For the present application, a cell has a large cross-section if its diameter or if the smallest distance separating two opposite faces of a cell, called width, is greater than or equal to 12.7 mm. According to one configuration, the cells of the first and second cellular structures 18, 20 have a width of the order of 19 mm. The cells of the first and second cellular structures 18, 20 have substantially the same cross-section.

[0036] According to a first arrangement visible on the figure 1 , the first and second faces 10.1, 10.2, 18.1, 18.2, 20.1, 20.2 of the acoustic panel 10 as well as of the first and second alveolar structures 18, 20 are flat.

[0037] According to a second arrangement visible on the figure 4 , the first and second faces 10.1, 10.2, 18.1, 18.2, 20.1, 20.2 of the acoustic panel 10 as well as of the first and second alveolar structures 18, 20 are curved.

[0038] According to one embodiment, the first acoustically resistive layer 14 and the second reflective layer 16 are joined at each of the first and second longitudinal edges 12.1, 12.2 of the acoustic panel 10.

[0039] According to one embodiment, at the second longitudinal edge 12.2 of the acoustic panel 10, the first and second faces of the first cellular structure 18 are not parallel to each other, but form an angle of less than 45° between them.

[0040] According to one embodiment, the acoustic panel 10 comprises at least one reinforcement 34 interposed between the first acoustically resistive layer 14 and the second reflective layer 16, between the first longitudinal edge 12.1 of the acoustic panel 10 and the first and second cellular structures 18, 20. This reinforcement 34 has a first surface 34.1 located approximately in the extension of the first face 20.1 of the second cellular structure 20, a second surface 34.2 located in the extension of the second face 18.2 of the first cellular structure 18, a third surface 34.3 in contact with the first edges 26.1, 28.1 of the first and second cellular structures 18, 20 as well as a fourth inclined surface 34.4 connecting the first and second surfaces 34.1, 34.2. The first surface 34.1 has a transverse dimension smaller than that of the second surface 34.2.

[0041] In the presence of a reinforcement 34, the first and second cellular structures 18, 20 do not need to have inclined edges 26.1, 28.1, which helps to avoid losses of acoustic treatment. In addition, the second cellular structure 20 is perfectly immobilized relative to the first cellular structure 18, between the recess 30 and the reinforcement 34. Thus, the first and second cellular structures 18, 20 are correctly positioned relative to each other and maintain this positioning, which helps to optimize the acoustic treatment.

[0042] The first surface 34.1 has a transverse dimension greater than 1 cm, less than 5 cm. This first surface 34.1 must have the smallest possible transverse dimension so as not to excessively alter the acoustic treatment and must be sufficiently wide to avoid a phenomenon of crushing the first and second alveolar structures 18, 20 with large alveoli.

[0043] The reinforcement 34 is a third cellular structure which has cells opening at the first and second surfaces 34.1, 34.2. The cells of the reinforcement 34 have a section smaller than that of the first and second cellular structures 18, 20. The cells of the reinforcement 34 have a width less than 11 mm. According to one configuration, the cells of the cellular structure of the reinforcement 34 have a width of between 3 and 6 mm.

[0044] In the presence of a reinforcement 34 in the form of a honeycomb structure, the acoustic panel 10 comprises a third zone Z3 at the right of the reinforcement 34. This zone Z3 can provide acoustic treatment if the first layer 14 is, at the right of the reinforcement 34, acoustically resistive and configured to allow acoustic waves to pass through.

[0045] According to one embodiment, the second reflective layer 16 is shaped like the second face 10.2 of the acoustic panel 10. In the presence of a reinforcement 34, the second reflective layer 16 comprises an extension 36 which extends beyond the second surface 34.2 of the reinforcement 34.

[0046] According to a first embodiment visible on the figure 1 , the first layer 14 extends continuously over the first and second honeycomb structures 18, 20, the fourth surface 34.4 of the reinforcement 34 and the extension 36 of the second reflective layer 16.

[0047] According to a second embodiment visible on the figure 3, the first layer 14 comprises a first part 38 acoustically resistive and porous to acoustic waves which extends over the first and second alveolar structures 18, 20 and at least partially over the first surface 34.1 of the reinforcement 34 as well as a second part 40, which may be non-porous, which extends at least partially over the first surface 34.1 of the reinforcement, over the fourth surface 34.4 of the reinforcement 34 and over the extension 36 of the reflective layer 16, the first and second parts 38, 40 comprising an overlapping zone 42 at the right of the first surface 34.1 of the reinforcement 34 where they are closely connected. Thus, the second part 40 ensures the junction between the first acoustically resistive part 38 and the second reflective layer 16.

[0048] According to the invention, the first and second cellular structures 18, 20 have simple shapes. The reinforcement 34 matches the shapes of the first and second cellular structures as well as the first and second layers 14, 16. The reinforcement 34 has all the complexities of the end of the panel (in terms of curvature, cutouts, slopes). Thus, the reinforcement 34 concentrates the complex shapes and singularities of the acoustic panel 10.

[0049] According to one method of operation, the first and second alveolar structures 18, 20 as well as the reinforcement 34 are produced independently of each other. The first alveolar structure 18 and the reinforcement 34 are machined by ultrasound to the final dimensions then the first and second alveolar structures 18, 20, the reinforcement 34 as well as the third acoustically resistive layer 22 are assembled in order to obtain a structure on which the second reflective layer 16 and the first acoustically resistive layer 14 are attached.

[0050] According to another operating method, the first and second alveolar structures 18, 20, the reinforcement 34 as well as the third acoustically resistive layer 22 are assembled then machined by ultrasound to the final dimensions once assembled.

[0051] Whatever the operating mode, the first acoustically resistive layer 14 and the second reflective layer 16 are positioned after the assembly of the first and second alveolar structures 18, 20, the reinforcement 34 as well as the third acoustically resistive layer 22.

[0052] The second reflective layer 16 can be obtained by draping or by a technique of placing fibers on the assembly of the first and second honeycomb structures 18, 20, the reinforcement 34 as well as the third acoustically resistive layer 22.

[0053] According to the first embodiment, the entire first layer 14 is obtained by draping or by a technique of placing fibers on the assembly of the first and second cellular structures 18, 20, the reinforcement 34 as well as the third acoustically resistive layer 22.

[0054] According to the second embodiment, the first portion 38 of the first acoustically resistive layer 14 is obtained by draping or by a fiber placement technique on the assembly of the first and second cellular structures 18, 20, the reinforcement 34 as well as the third acoustically resistive layer 22. The second portion 40 of the first layer 14 is produced by draping or by a fiber placement technique. It is then attached to the assembly of the first and second cellular structures 18, 20, the reinforcement 34 as well as the third acoustically resistive layer 22, then connected to the extension 36 of the second reflective layer 16 and to the first portion 38 of the first acoustically resistive layer 14 at the overlap zone 42.

Claims

1. Acoustic panel comprising a first longitudinal edge (12.1), a first acoustically resistive layer (14), a second reflective layer (16), at least first and second cellular structures (18, 20) interposed between the first and second layers (14, 16), and at least a third acoustically resistive layer (22) interposed between the first and second cellular structures (18, 20), the first acoustically resistive layer (14) and the second reflective layer (16) being contiguous at the first longitudinal edge (12.1), the first cellular structure having a first face (18.1), a second face (18.2) that is opposite to the first face (18.1) and that is in contact with the second reflective layer (16), and a first edge face (28.1) oriented toward the first longitudinal edge (12.1) of the acoustic panel (10), the second cellular structure (20) comprising a first face (20.1) in contact with the first acoustically resistive layer (14) and a second face (20.2) opposite to the first face (20.1), and also first and second edge faces (26.1, 26.2) connecting the first and second faces (20.1, 20.2), the first edge face (26.1) of the second cellular structure (20) being oriented toward the first longitudinal edge (12.1) of the acoustic panel (10); wherein the first cellular structure (18) comprises a set-back portion (30) which extends from the first face (18.1) in the direction of the second face (18.2) and which forms a recess (32) dimensioned to accommodate the second cellular structure (20) and the third acoustically resistive layer (22), the second cellular structure (20) being positioned in the recess (32) in such a way that the first faces (18.1, 20.1) of the first and second cellular structures (18, 20) are coplanar and in contact with the first acoustically resistive layer (14), that the first edge faces (26.1, 28.1) of the first and second cellular structures (18, 20) are coplanar and that the second edge face (26.2) of the second cellular structure (20) is in contact with the set-back portion (30).

2. Acoustic panel as claimed in claim 1, wherein the acoustic panel comprises at least one reinforcement (34) interposed between the first acoustically resistive layer (14) and the second reflective layer (16), between the first longitudinal edge (12.1) of the acoustic panel (10) and the first edge faces (26.1, 28.1) of the first and second cellular structures (18, 20), the reinforcement (34) having a first surface (34.1) extending in a plane common to the first face (20.1) of the second cellular structure (20), a second surface (34.2) extending in a plane common to the second face (18.2) of the first cellular structure (18), a third surface (34.3) in contact with the first edge faces (26.1, 28.1) of the first and second cellular structures (18, 20), and a fourth inclined surface (34.4) connecting the first and second surfaces (34.1, 34.2).

3. Acoustic panel as claimed in the preceding claim, wherein the first surface (34.1) has a transverse dimension greater than 1 cm and smaller than 5 cm.

4. Acoustic panel as claimed in claim 2 or 3, wherein the reinforcement (34) is a cellular structure which has cells opening out at the first and second surfaces (34.1, 34.2) of the reinforcement (34).

5. Acoustic panel as claimed in the preceding claim, wherein the cells of the reinforcement (34) have a cross section smaller than that of the first and second cellular structures (18, 20).

6. Acoustic panel as claimed in the preceding claim, wherein the cells of the reinforcement (34) have a width of between 3 and 6 mm.

7. Acoustic panel as claimed in one of claims 2 to 6, wherein the second, reflective layer (16) comprises an extension (36) which extends beyond the second surface (34.2) of the reinforcement (34).

8. Acoustic panel as claimed in the preceding claim, wherein the first layer (14) extends continuously over the first and second cellular structures (18, 20), the fourth surface (34.4) of the reinforcement (34) and the extension (36) of the second, reflective layer (16).

9. Acoustic panel as claimed in claim 7, wherein the first layer (14) comprises a first acoustically resistive part (38) which extends over the first and second cellular structures (18, 20) and at least partially over the first surface (34.1) of the reinforcement (34), and a second part (40) which extends at least partially over the first surface (34.1) of the reinforcement (34), over the fourth surface (34.4) of the reinforcement (34) and over the extension (36) of the reflective layer (16), the first and second parts (38, 40) having a zone of overlap (42) in line with the first surface (34.1) of the reinforcement (34).

10. Acoustic panel as claimed in one of the preceding claims, wherein the first and second cellular structures (18, 20) have cells having a width greater than or equal to 12.7 mm.

11. Aircraft comprising at least one acoustic panel as claimed in one of the preceding claims.