Acoustic panel comprising acoustic elements with a constant cross-section

Abstract

Acoustic panel comprising acoustic elements with constant cross-section. The invention relates to an acoustic panel (1000) comprising acoustic cells (1) interposed between an acoustic skin (100) and a closing skin (300), the skins (100, 300) extending longitudinally along a first direction (D1) and transversely along a second direction (D2), a plurality of hollow acoustic elements (220) being arranged in the acoustic cells (1), the acoustic panel (1000) being characterized in that the cross-section of the acoustic elements (220) is identical in all planes perpendicular to the first direction (D1). Figure for the abstract: Fig. 1

Description

Title of the invention: Acoustic panel comprising acoustic elements with a constant cross-section technical field

[0001] The present invention relates to the general field of acoustic attenuation panels. More particularly, it relates to acoustic panels used to reduce noise produced in aircraft engines, such as turbines or exhaust systems, in the compressor section, the cowling, or the nacelle. It may also relate to acoustic panels used in ventilation systems. Previous technique

[0002] Acoustic attenuation panels typically consist of a plate or skin with an acoustic surface permeable to the acoustic waves to be attenuated and a solid reflective plate or skin, known as the "closing plate," with a multicellular body positioned between these two surfaces. The multicellular body is generally composed of a series of partitions, for example, honeycomb-shaped, delimiting a plurality of cells. As is well known, such panels form Helmholtz resonators that attenuate acoustic waves within a certain frequency range, the height of the cavities allowing the selection of the targeted frequency band. Acoustic attenuation panels of this type are described in particular in US patent 5,912,442 and GB patent 2,314,526. Thus, the lower the frequency bands to be attenuated, the greater the height of the cavities will be.

[0003] These acoustic attenuation panels, limited to simple cell shapes such as NIDA-type honeycomb cells, are not suitable for very low frequencies due to the required cavity height and resulting bulk. This is particularly true for acoustic attenuation panels in high-bypass turbojet engines, where the fundamental frequency of the fan to be absorbed is between 200 Hz and 400 Hz, and where the available space is limited.

[0004] One solution for handling low frequencies without using an excessively thick multicellular body is to place hollow acoustic elements extending between a base and an apex, for example open truncated cones, within the cells of the multicellular body. Such hollow acoustic elements are described in particular in documents FR 3 082 987, FR 3 127 713, FR 3 129 022 and FR 3 129 315.

[0005] However, such hollow acoustic elements are only effective for a restricted frequency band, and are difficult to manufacture. Description of the invention

[0006] The present invention aims to remedy the aforementioned drawbacks by providing a compact acoustic panel that is effective over a wide range of frequencies and easy to manufacture.

[0007] To this end, the invention proposes an acoustic panel comprising an acoustic skin and a closing skin extending longitudinally in a first direction and transversely in a second direction, the acoustic panel further comprising an acoustic component disposed between the acoustic skin and the closing skin, the acoustic component comprising a plurality of partitions extending in a third direction perpendicular to the first and second directions between a lower end and an upper end, the lower ends of the partitions being in contact with the closing skin, the acoustic panel defining a plurality of acoustic cells delimited in the second direction by two consecutive partitions of the acoustic component, the acoustic panel further comprising a plurality of hollow acoustic elements disposed in the acoustic cells,the acoustic panel being characterized in that each hollow acoustic element comprises a first edge and a second edge each extending in a plane defined by the first and second directions from the upper end of the partitions of one of the cells, and in that each hollow acoustic element comprises a third edge extending from a distal end of the first edge and a fourth edge extending from a distal end of the second edge, the third and fourth edges extending in the direction of the closing skin to a free end.

[0008] Thus, the acoustic panel as described treats a wide range of sound frequencies while remaining compact, thanks to its hollow acoustic elements. Their particular shape makes them very easy to manufacture. The overall structure of the acoustic component results in a robust and solid acoustic panel that is also easy to manufacture.

[0009] Preferably, the cross-section of each acoustic element is identical in all planes perpendicular to the first direction.

[0010] According to one possible aspect of the invention, the plurality of partitions of the acoustic component comprises first partitions extending lengthwise along the first direction and second partitions extending lengthwise along the second direction, the acoustic cells being delimited along the first direction by two consecutive second partitions of the acoustic component.

[0011] The second partitions allow the acoustic cells to be separated along the first direction. Such partitioning eliminates cavity modes along the first direction and provides locally responsive acoustic treatment. Thus, the acoustic treatment is better controlled, and therefore more efficient and optimal. Furthermore, the second partitions improve the mechanical strength of the acoustic component. When the acoustic component is assembled to form an acoustic panel, the second partitions allow the mechanical forces between the acoustic skin and the closing skin or wall to be transferred.

[0012] According to another possible aspect of the invention, the first, second, third and fourth edges of the hollow acoustic elements extend along the first direction from one of the second partitions of the acoustic component to the second consecutive partition of the acoustic component.

[0013] The manufacture of the acoustic panel is thus facilitated and its performance is improved.

[0014] According to another possible aspect of the invention, the acoustic panel further comprises support elements extending along the third direction from the upper edges of the partitions of the acoustic component to the acoustic skin so as to keep the acoustic skin away from the acoustic elements.

[0015] Such a spacing between the acoustic skin and the acoustic elements can accommodate an interposition layer.

[0016] Such spacing also allows for better control of the acoustic behavior of the acoustic panel, as it keeps the acoustic component away from the fluid flow in the channel. Furthermore, even without an interposed layer, the spacing between the acoustic skin and the acoustic component adds an extra degree of freedom to the acoustic panel, thus widening the attenuated frequency band.

[0017] According to another possible aspect of the invention, the acoustic panel further comprises an interposition layer disposed between the acoustic elements and the acoustic skin.

[0018] The interposition layer makes it possible to equalize the impedance over a wide frequency band. Thus, the acoustic panel can process and attenuate a wider range of sound frequencies.

[0019] According to another possible aspect of the invention, the interposition layer is a wire mesh, a lattice or a woven fibrous texture.

[0020] According to another possible aspect of the invention, for at least a portion of the hollow acoustic elements, the distance along the second direction between the distal ends of the first edge and the second edge is greater than or equal to the distance along the second direction between the free ends of the third edge and the fourth edge.

[0021] Thus, the hollow acoustic elements have a convergent shape. The distance along the second direction between the distal ends of the first edge and the second edge can be strictly greater than the distance along the second direction between the free ends of the third edge and the fourth edge.

[0022] According to another possible aspect of the invention, for at least a part of the hollow acoustic elements, the distance along the second direction between the distal ends of the first edge and the second edge is less than or equal to the distance along the second direction between the free ends of the third edge and the fourth edge.

[0023] Thus, the hollow acoustic elements have a divergent shape. The distance along the second direction between the distal ends of the first edge and the second edge can be strictly less than the distance along the second direction between the free ends of the third edge and the fourth edge.

[0024] According to another possible aspect of the invention, the third and fourth edges of at least a part of the hollow acoustic elements are curved.

[0025] According to another possible aspect of the invention, the third and fourth edges of at least a part of the hollow acoustic elements are straight.

[0026] The shape and spacing between the third and fourth edges define the mass of air set in motion between the third and fourth edges. This mass of air directly determines the resistance to the passage of the wave and the frequencies at which resonances will occur.

[0027] According to another possible aspect of the invention, a part of the acoustic cells of the acoustic component has a first height along the third direction and another part of the acoustic cells of the acoustic component has a second height along the third direction different from the first height.

[0028] Thus, the frequencies attenuated by the acoustic panel can be adapted locally.

[0029] Of course, the acoustic component may include other acoustic cells having different heights from the first and second heights. Each part of the acoustic cells may comprise a single acoustic cell.

[0030] According to another possible aspect of the invention, a part of the acoustic cells of the acoustic component includes third and fourth edges having a first shape and another part of the acoustic cells of the acoustic component includes third and fourth edges having a second shape different from the first shape.

[0031] Thus, the frequencies attenuated by the acoustic panel can be adapted locally.

[0032] Of course, the acoustic component may include other acoustic cells comprising third and fourth edges having shapes different from the first and second shapes. Each part of the acoustic cells may comprise a single acoustic cell. Brief description of the drawings

[0033] [Fig-1] Fig. 1 is a schematic exploded perspective view of a panel acoustics according to the invention.

[0034] [Fig.2] Fig.2 is a schematic cross-sectional view of the acoustic panel of the [Fig.l].

[0035] [Fig.3] Fig.3 is a schematic perspective view of an acoustic cell of the acoustic panel of figures 1 and 2.

[0036] [Fig.4] Fig.4 is a schematic perspective view of an acoustic cell according to one variant.

[0037] [Fig. 5] Fig. 5 is a schematic perspective view of an acoustic cell according to another variant.

[0038] [Fig. 6] Fig. 6 is a schematic perspective view of an acoustic cell according to one variant.

[0039] [Fig. 7] Fig. 7 is a schematic cross-sectional view of an acoustic component according to the invention comprising acoustic cells of different types and different heights.

[0040] [Fig.8] Fig.8 is a schematic cross-sectional view of the acoustic panel of the [Fig.l] comprising an interposition layer disposed in contact with the acoustic skin and the acoustic component.

[0041] [Fig.9] Fig.9 is a schematic cross-sectional view of the acoustic panel of the [Fig.l] comprising an interposition layer disposed in contact with the acoustic component and at a distance from the acoustic skin. Description of the implementation methods

[0042] Figures 1 and 2 illustrate an example of an acoustic panel 1000. The acoustic panel 1000 comprises an acoustic skin 100, an acoustic component 200 and a closing skin 300.

[0043] The acoustic skin 100 has the function of allowing the sound waves to be attenuated to pass through the acoustic component 200. For this purpose, the acoustic skin 100 comprises a plurality of perforations 111, as illustrated in Figures 1 and 2. The acoustic skin 100 can have a thickness of between 1 mm and 5 mm, for example 2 mm.

[0044] The closing skin 300 corresponds to a solid surface designed to reflect sound waves entering the acoustic component 200. The closing skin 300 may correspond to a surface of an object, for example, an aircraft engine. In the latter case, the acoustic panel is formed by mounting the acoustic skin 100 and the acoustic component 200 onto said object.

[0045] The acoustic skin 100 and the closing skin 300 can extend parallel to each other. The acoustic skin 100 extends longitudinally along a first direction Di and transversely along a second direction D2 perpendicular to the first direction Di. The closing skin 300 extends longitudinally along the first direction Di and transversely along the second direction D2.

[0046] The acoustic skin 100 and the closing skin 300 can be flat, i.e., the first and second directions Di and D2 are straight. The acoustic skin 100 and the closing skin 300 can be curved. Thus, the first direction Di and / or the second direction D2 can be curved. In particular, the first direction Di can be straight and the second direction D2 can be curved. Conversely, the first direction Di can be curved and the second direction D2 can be straight. The first direction Di and the second direction D2 can be curved.

[0047] The acoustic component 200 comprises a plurality of partitions 210. The partitions 210 extend vertically along a third direction D3 perpendicular to the first and second directions Di and D2. The third direction D3 is rectilinear. The partitions 210 extend along the third direction D3 between an upper end 210a and a lower end 210b. The lower ends 210b of the partitions 210 of the acoustic component 200 are in contact with the closing skin 300.

[0048] The plurality of partitions 210 includes first partitions 211 which extend lengthwise along the first direction Db. The plurality of partitions 210 may include second partitions 212 which extend lengthwise along the second direction D2.

[0049] The acoustic component 200 defines acoustic cells 1. [Fig.3] illustrates an example of an acoustic cell 1 of the acoustic component 200.

[0050] The acoustic cells 1 extend along the second direction D2 between two consecutive partitions 211. The acoustic cells 1 extend along the second direction D2 over a second non-zero distance Li2. The non-zero distance Li2 can be a curvilinear length if the second direction D2 is curved.

[0051] If the acoustic component 200 includes second partitions 212, the acoustic cells 1 extend along the first direction Di between two consecutive second partitions 212. The acoustic cells 1 extend along the first direction Di over a first non-zero distance Lu. The non-zero distance Lu can be a curvilinear length if the first direction Di is curved.

[0052] The acoustic cells 1 extend along the third direction D3 between a bottom and an upper end. The bottom of the acoustic cells 1 is formed by a portion of the closing skin 300. The upper end of the acoustic cells 1 is open and allows sound waves to pass through. The upper end of the acoustic cells 1 is at the level of the upper ends 210a of the partitions 210 of the acoustic component 120. The acoustic cells 1 extend along the third direction D3 over a third non-zero distance Ln.

[0053] The acoustic cells 1 are preferably open only at their upper end. In particular, sound waves can enter and exit the acoustic cells 1 only through the upper end of said acoustic cells 1. Thus, the partitions 210 of the acoustic component 200 are free of through-holes. The partitions 210 of the acoustic component 200 are impermeable to fluids. Thus, no opening interferes with the processing of sound waves. The closing skin 300 is free of through-holes. The closing skin 300 is impermeable to fluids. Thus, no opening interferes with the processing of sound waves.

[0054] The acoustic component 200 further comprises a plurality of acoustic elements 220. Each acoustic element 220 is arranged in an acoustic cell 1. Each acoustic element 220 is formed by a first edge 221, a second edge 222, a third edge 223 and a fourth edge 224.

[0055] The first edge 221 and the second edge 222 extend in a plane defined by the first and second directions Di and D2. The first edge 221 and the second edge 222 are parallel. The first edge 221 and the second edge 222 extend lengthwise parallel to each other along the first direction Db. The first and second edges 221, 222 extend along the second direction D2 from the upper end 210a of one of the partitions 210. In particular, the first and second edges 221, 222 extend along the second direction D2 from the upper end 210a of one of the first partitions 211. The first edge 221 and the second edge 222 belonging to the same acoustic element 220 extend along the second direction D2 from the upper end 210a of two consecutive partitions 210.In particular, the first edge 221 and the second edge 222 belonging to the same acoustic element 220 extend along the second direction D2 from the upper end 210a of two consecutive first partitions 211. Thus, the first edge 221 extends from the upper end 210a of a partition 210 and the second edge 222 extends from the upper end 210a. of another partition 210. The first and second edges 221 and 222 of the same acoustic element 210 extend towards each other along the second direction D2.

[0056] The first edge 221 extends along the second direction D2 from the upper end 210a of one of the partitions 210 to a distal end. The second edge 222 extends along the second direction D2 from the upper end 210a of one of the partitions 210 to a distal end. The distal ends of the first edge 221 and the second edge 222, belonging to the same acoustic element 220, are positioned opposite each other. The distal ends of the first edge 221 and the second edge 222, belonging to the same acoustic element 220, are separated by a non-zero fourth distance Wn along the second direction D2. The first edge 221 is not in contact with the second edge 222.

[0057] If the acoustic component 200 comprises second partitions 212, the first and second edges 221 and 222 can extend along the first direction Di between two consecutive second partitions 212. In particular, the first and second edges 221 and 222 can extend along the third direction D3 from one second partition 212 to the next second partition 212.

[0058] The first and second edges 221 and 222 partially delimit the upper end of the acoustic cells 1. Thus, the only opening in the acoustic cells 1 is the space between the distal ends of the first and second edges 221 and 222. In particular, sound waves can enter and exit the acoustic cells 1 only through the space between the distal ends of the first and second edges 221 and 222. Thus, the first and second edges 221 and 222 of the hollow acoustic elements 220 are devoid of through-holes. The first and second edges 221 and 222 of the hollow acoustic elements 220 are impermeable to fluids. Thus, no opening interferes with the processing of sound waves.

[0059] Preferably, the first and second edges 221 and 222 are symmetrical with respect to each other along a plane of symmetry defined by the first and third directions Di and D3.

[0060] The third edge 223 extends from the distal end of the first edge 221 to a free end. The fourth edge 224 extends from the distal end of the second edge 222 to a free end. The third edge 223 and the fourth edge 224 extend in the direction of the closing skin 300. Thus, the free ends of the third and fourth edges 223 and 224 are present in the acoustic cell 1. The third edge 223 and the fourth edge 224 are arranged opposite each other. The third and fourth edges 223 and 224 extend along the third direction D3 over a non-zero height Hh

[0061] The third and fourth edges 223 and 224 of the same acoustic element 220 are opposite each other along the second direction D2. The free ends of the third and fourth edges 223 and 224 belonging to the same acoustic element 220 are separated by a non-zero fifth distance Wi2 along the second direction D2. The third edge 223 is not in contact with the fourth edge 224.

[0062] The third and fourth edges 223 and 224 extend lengthwise parallel to each other along the first direction Dp. If the acoustic component 200 includes second partitions 212, the third and fourth edges 223 and 224 can extend along the first direction Di between two consecutive second partitions 212. In particular, the third and fourth edges 223 and 224 can extend along the third direction D3 from one second partition 212 to the next second partition 212.

[0063] Thus, sound waves can enter and exit the acoustic cells 1 only by crossing the space between the third and fourth edges 223 and 224 of the acoustic elements 220.

[0064] The third and fourth edges 223 and 224 of the hollow acoustic elements 220 are free of through-holes. The third and fourth edges 223 and 224 of the hollow acoustic elements 220 are impermeable to fluids. Thus, no opening interferes with the processing of sound waves.

[0065] Preferably, the third and fourth edges 223 and 224 are symmetrical with respect to each other along a plane of symmetry defined by the first and third directions Di and D3. Thus, the hollow acoustic elements 220 each exhibit symmetry along a plane of symmetry defined by the first and third directions Di and D3. Said plane of symmetry is situated between, on the one hand, the first and third edges 221 and 223 and, on the other hand, the second and fourth edges 222 and 224.

[0066] The geometry of the hollow acoustic elements 220 is defined so that the cross-section of the acoustic elements is identical in all planes perpendicular to the first direction Dh, i.e., in all planes including the second and third directions D2 and D3. Thus, the first, second, third and fourth edges 221, 222, 223, 224 of the acoustic elements 220 are free of orifices extending along the second or third directions D2 and D3, or more generally along any direction intersecting the first direction Db. Thus, no orifice interferes with the processing of sound waves.

[0067] Preferably, the first distance Lu and the second distance L[2] are close so as to obtain an acoustic cell 1 with a square or almost square cross-section. In particular, the first distance Lu can correspond to between 50% and 200% of the second distance Li2, or even to between 80% and 120% of the second distance L12.

[0068] Preferably, the first distance Lu is strictly less than the ratio of the speed of sound to twice the maximum frequency of the sound wave to be attenuated. Similarly, the second distance Li2 is preferably strictly less than the ratio of the speed of sound to twice the maximum frequency of the sound wave to be attenuated. This maximum frequency may be lower than the cutoff frequency so as to avoid higher modes.

[0069] The first distance Lu can be less than or equal to 50 mm. The second distance L12 can be less than or equal to 50 mm. These values ​​are particularly suitable for a turbojet application, especially for an application in an aircraft turbojet nacelle. These values ​​are particularly suitable for frequencies less than or equal to 1000 Hz.

[0070] To facilitate the manufacture of the acoustic panel and limit its mass, the first distance Lu can be greater than or equal to 10 mm. For the same reasons, the second distance Ln can be greater than or equal to 10 mm. For the same reasons, the third distance Lu can be greater than or equal to 5 mm.

[0071] Preferably, at least the fourth distance Wn or the fifth distance W[2 is greater than 1 mm. More generally, the spacing between the third edge 223 and the fourth edge 224 along the second direction D2 is preferably greater than 1 mm over the entire height Hi of said third and fourth edges 223 and 224. Thus, manufacturing tolerances are easier to control. Furthermore, too small a spacing between the third and fourth edges results in excessively high acoustic resistance. There is then a risk that the acoustic waves will no longer be attenuated by the acoustic panel, but reflected.

[0072] In order to improve the performance of the acoustic cells 1, the fourth distance Wn and the fifth distance W[2 can be strictly less than the second direction Li2 minus 2 mm, i.e., max(Wn ;Wi2) < L[2 - 2 mm. Indeed, it is preferable that the third and fourth edges 223 and 224 not be too close to the first partitions 211 to allow good propagation of sound waves inside the acoustic cell.

[0073] It is preferable to avoid a slope of the third and fourth edges 223 and 224 that is too steep. Therefore, it is preferable to verify the following relationship:

[0074] [Math.l] arctan

[0075] Figures 1 to 3 illustrate a particular example of acoustic cells 1. The invention is of course not limited to this particular example of an acoustic cell. Figures 4 to 6 illustrate other examples of acoustic cells 2, 3 and 4 which have the same characteristics as those indicated previously for acoustic cells 1.

[0076] Figure 4 illustrates an example of an acoustic cell 2 comprising an acoustic element 320. As defined previously, the acoustic element 320 comprises a first edge 321, a second edge 322, a third edge 323, and a fourth edge 324. The distal ends of the first and second edges 321 and 322 are separated by a non-zero distance W2i along the second direction D2. The free ends of the third and fourth edges 323 and 324 are separated by a non-zero distance W22 along the second direction D2. The third and fourth edges 323 and 324 extend along the third direction D3 over a non-zero height H2.

[0077] Figure 5 illustrates an example of an acoustic cell 3 comprising an acoustic element 420. As defined previously, the acoustic element 420 comprises a first edge 421, a second edge 422, a third edge 423, and a fourth edge 424. The distal ends of the first and second edges 421 and 422 are separated by a non-zero distance W3 along the second direction D2. The free ends of the third and fourth edges 423 and 424 are separated by a non-zero distance W32 along the second direction D2. The third and fourth edges 423 and 424 extend along the third direction D3 over a non-zero height H3.

[0078] Figure 6 illustrates an example of an acoustic cell 4 comprising an acoustic element 520. As defined previously, the acoustic element 520 comprises a first edge 521, a second edge 522, a third edge 523, and a fourth edge 524. The distal ends of the first and second edges 521 and 522 are separated by a non-zero distance W4i along the second direction D2. The free ends of the third and fourth edges 523 and 524 are separated by a non-zero distance W42 along the second direction D2. The third and fourth edges 523 and 524 extend along the third direction D3 over a non-zero height H4.

[0079] The third and fourth edges can follow a straight trajectory in the planes perpendicular to the first direction Db, that is to say in the planes defined by the second and third directions D2 and D3. This is the case for the acoustic elements 220 and 320 illustrated in Figures 3 and 4.

[0080] On the contrary, the third and fourth edges can follow a non-rectilinear trajectory in planes perpendicular to the first direction Db, that is, in the planes defined by the second and third directions D2 and D3. In particular, the third and fourth edges can follow a curved trajectory in the planes perpendicular to the first direction Dh, that is to say in the planes defined by the second and third directions D2 and D3. This is the case for the acoustic elements 420 and 520 illustrated in figures 5 and 6.

[0081] Acoustic elements may have a convergent geometry. This is the case for acoustic elements 220 and 520 illustrated in Figures 3 and 6. The fourth distance Wn or W4[ is then greater than the fifth distance W[2 or W42.

[0082] On the contrary, the acoustic elements may have a divergent geometry. This is the case for the acoustic elements 320 and 420 illustrated in Figures 4 and 5. The fourth distance W2i or W3i is then less than the fifth distance W22 or W32.

[0083] We do not, of course, depart from the scope of the invention if the fourth distance is equal to the fifth distance (not shown). In this case, the spacing along the second direction D2 between the third and fourth edges can be constant along the third direction D3. Conversely, the spacing along the second direction D2 between the third and fourth edges can be variable along the third direction D3.

[0084] We do not, of course, depart from the scope of the invention if the third and fourth edges have more complex shapes than those illustrated in the figures.

[0085] It is of course not beyond the scope of the invention if the acoustic component has several different types of acoustic cells. For example, the acoustic component according to the invention may have acoustic cells 1 and acoustic cells 2. Figure 7 illustrates an example of an acoustic component 200bis comprising two types of acoustic cells, in particular acoustic cells 3 and acoustic cells 4. The acoustic component may, on the contrary, comprise only identical acoustic cells, as illustrated in Figures 1, 2, 8 and 9.

[0086] Thus, a single acoustic component may comprise some acoustic cells having a third and fourth edge of a first shape and other acoustic cells having a third and fourth edge of a second shape different from the first shape. In particular, a single acoustic component may comprise acoustic cells of different types along the second direction. A single acoustic component may also comprise acoustic cells of different types along the first direction.

[0087] In the example illustrated in Figures 1, 2, 8 and 9, all the acoustic cells of the acoustic component have the same height L[3 along the third direction D3. However, it does not depart from the scope of the invention if the acoustic cells of the same acoustic component have different heights along the third direction D3. In particular, a first plurality of acoustic cells of an acoustic component according to the invention may have a first height along the third direction D3 that differs from a second height along the third direction D3 exhibited by a second plurality of acoustic cells of the same acoustic component. Figure 7 illustrates an example of an acoustic component 200bis comprising a first plurality Pi of acoustic cells 3, 4 having a first height LP1 along the third direction D3 and a second plurality P2 of acoustic cells 3, 4 having a second height LP2 along the third direction D3 that differs from the first height LP1.

[0088] In particular, a single acoustic component may comprise acoustic cells of different heights along the second direction. A single acoustic component may also comprise acoustic cells of different heights along the first direction.

[0089] Preferably, even when the acoustic component 200bis of an acoustic panel has acoustic cells of different heights, the distance between the acoustic skin and the closing skin or wall remains constant. This constant distance between the acoustic skin and the closing skin or wall can then be achieved by means of support elements 230bis such as those described below.

[0090] The acoustic skin 100 can rest on the first and second edges 221, 222 of the acoustic elements 120. Thus, the acoustic skin 100 is in contact with the acoustic cells 1.

[0091] However, the acoustic skin 100 is preferably positioned at a distance from the acoustic cells 1, as illustrated in Figures 1 and 2. Thus, the acoustic skin 100 is spaced from the acoustic cells 1 by a non-zero distance along the third direction D3. The acoustic skin 100 is then spaced from the first and second edges 221 and 222 of the acoustic elements 220 by a non-zero distance along the third direction D3. This distance is preferably greater than 5 mm. Such a distance can add an additional degree of freedom to the acoustic panel, and thus broaden the attenuated frequency band. The acoustic component is also less affected by the flow of external fluids grazing the acoustic panel.

[0092] In order to ensure spacing between the acoustic cells 1 and the acoustic skin 100, support elements 230 can be interposed between the acoustic cells 1 and the skin 100. In particular, the support elements 230 extend from the acoustic cells 1 to the acoustic skin 100. The height of the support elements 230 along the third direction D3 is preferably greater than 5 mm, in order to facilitate the manufacture of said support elements.

[0093] The support elements 230 can take the form of partitions extending along the third direction D3 to the acoustic skin 100. The support elements 230 can include first support elements 231 extending lengthwise along the first direction Db as illustrated in Figures 1 and 2. The support elements 230 can include second support elements 232 extending lengthwise along the second direction D2, as illustrated in [Fig. 1]. The support elements 230 can form a network of partitions.

[0094] The support elements 230 extend along the third direction D3 between an upper end and a lower end. The lower ends of the support elements 230 are in contact with the acoustic cells 1, and the upper ends of the support elements 230 are in contact with the acoustic skin 100. The lower ends of the support elements 230 may be in contact with the upper ends of the partitions 220 of the acoustic component 200. The lower ends of the support elements 230 may only be in contact with the upper ends of the partitions 220 of the acoustic component 200. Such a configuration facilitates the manufacture of the acoustic panel and improves its mechanical strength.

[0095] Preferably, the support elements 230 cover only a part of the upper ends of the partitions 210 of the acoustic component 200.

[0096] The support elements 230 can delimit closed spaces along the first and second directions Di and D2.

[0097] The support elements 230 can be part of the acoustic component 200.

[0098] An interposition layer 400, 500 can be interposed between the acoustic skin 100 and the acoustic cells 1, as illustrated in the acoustic panel 2000 of [Fig. 8] or in the acoustic panel 3000 of [Fig. 9]. The interposition layer 400, 500 can be in the form of several distinct interposition layer portions. In particular, if the support elements 230 delimit enclosed spaces as described above, an interposition layer portion can be present in each enclosed space.

[0099] The interposition layer 400, 500 may be present even if the acoustic panel does not include support elements 230. It is then the interposition layer which makes it possible to keep the acoustic skin 100 away from the acoustic cells 1.

[0100] The interposition layer may be in contact with the acoustic skin 100 and at a non-zero distance from the acoustic cells 1, in particular at a non-zero distance from the first and second edges 221 and 222 of the hollow acoustic elements 220. Conversely, as in the example illustrated in [Fig. 9], the interposition layer 500 may be at a non-zero distance from the acoustic skin 100 and in contact with the acoustic cells 1, in particular be in contact with the first and second edges 221 and 222 of the hollow acoustic elements 220. The interposition layer 400 can also be simultaneously in contact with the acoustic skin 100 and the acoustic cells 1, in particular in contact with the first and second edges 221 and 222 of the hollow acoustic elements 220, as in the example illustrated in [Fig.8].

[0101] The interposition layer 400, 500 may, for example, be a wire mesh or lattice, for example made of metal. The interposition layer 400, 500 may, for example, be a woven fibrous texture, for example made of Kevlar fibers. The interposition layer 400, 500 may be a fabric made of an organic material, for example polyaryletherketone (PAEK), polyetherketoneketone (PEKK), polyetherimide (PEI), polyphenylene sulfide (PPS), or polyethersulfone (PESU). The interposition layer 400, 500 preferably withstands temperatures up to at least 80°C, or even up to at least 120°C. The interposition layer 400, 500 is preferably made of a material that is not very sensitive to moisture.

[0102] The 400, 500 interposition layer is an acoustically resistive layer. Such a 400, 500 interposition layer allows for impedance uniformity over a wide frequency band. Thus, the 2000, 3000 acoustic panel can process and attenuate a wider range of sound frequencies.

[0103] Figures 1, 2, 8 and 9 illustrate only four rows of acoustic cells by way of illustration. It is of course not outside the scope of the invention if the acoustic panel comprises more or less than four rows of acoustic cells.

[0104] Several materials and processes are possible for producing the acoustic panel of the invention.

[0105] The acoustic skin 100 can be produced in a well-known manner by stamping, by automated fiber placement (AFP), or by automated tape laying (ATL). Other processes can also be used to manufacture the acoustic skin 100, such as manual laying.

[0106] The acoustic skin 100 can be made of a composite material comprising fibers, for example, a composite material comprising fibers impregnated with a thermoplastic or thermosetting resin. The fibers can be made of carbon, glass, or aramid. The acoustic skin 100 may not comprise fibers. The thermoplastic matrix can be made, for example, of polyaryletherketone (PAEK), polyetherketoneketone (PEKK), polyetherimide (PEI), polyphenylene sulfide (PPS), polyethersulfone (PESU), or polycarbonate (PC).

[0107] The closure skin 300 can be produced in a well-known manner by stamping, by automatic fiber placement called "AFP" for "Automated Fiber Placement", or by automatic tape draping called "ATL" for "Automated Tape Lying". Other processes can also be used to manufacture the closure skin 300. For example, the closure skin can be pre-baked and then bonded to the acoustic component 200, or it can be formed and baked directly onto the acoustic component 200.

[0108] The closing skin 300 may be made of a composite material comprising fibers, for example, a composite material based on carbon fibers impregnated with a thermoplastic or thermosetting resin. The closing skin 300 may not comprise fibers. The closing skin 300 may comprise all the fiber types and all the matrix types described previously for the acoustic skin 100. The closing skin 300 may also comprise other fiber types and matrix types than those described previously.

[0109] The acoustic component 200 can be produced in a well-known manner by additive manufacturing, injection, extrusion or stamping.

[0110] The acoustic component 200 can be manufactured using a well-known injection-compression process with a thermoplastic material. Injection-compression involves injecting the material into a partially open mold. Thus, even though the material solidifies rapidly upon contact with the mold due to the significant temperature difference between the tooling and the molten material, the mold cavity becomes less obstructed, and the pressure required for injecting the material remains acceptable. Once the entire volume of material is injected into the cavity and generally distributed throughout the mold, the mold is completely closed by a closing force to force the material into the most complex areas and return to the correct dimensions. This allows for thinner wall thicknesses for acoustic components than with a conventional injection molding process.

[0111] The acoustic component 200 can be produced in a well-known manner by injection molding with temperature control of the molding from a thermoplastic material. Injection molding with temperature control of the molding consists of controlling the temperature of the molding or the mold by means of a mold temperature control system, for example with a heat transfer fluid or with air.

[0112] The acoustic component 200 is preferably made of a thermoplastic material to facilitate its manufacture. The acoustic component 200 is preferably made of an amorphous thermoplastic material to facilitate its shaping. The acoustic component 200 can, for example, be made of polyetherimide (PEI) or polyethersulfone (PESU) to facilitate its manufacture and shaping after fabrication.

[0113] The acoustic component 200 and the closing skin 300 can be formed in one piece, for example by additive manufacturing or injection molding. Otherwise, the component Acoustic 200 and closing skin 300 can be assembled in a well-known manner by gluing, welding or simultaneously by gluing and welding.

[0114] The acoustic component 200 and the support elements 230 can be formed as a single piece, for example by additive manufacturing, injection molding, or stamping. Alternatively, the acoustic component 200 and the support elements 230 can be assembled in a well-known manner by bonding, welding, or simultaneously by bonding and welding.

[0115] The acoustic skin 100 can be assembled by gluing, welding or simultaneously by gluing and welding.

[0116] The acoustic panel can, for example, be used for sound attenuation in an aircraft nacelle or engine, for a blade platform, or for an aircraft sleeve. The acoustic panel can also be used for sound attenuation in a ventilation and / or air conditioning system.

[0117] The expression "between ... and ..." should be understood as including the boundaries.

Claims

Demands

1. Acoustic panel (1000) comprising an acoustic skin (100) and a closing skin (300) extending longitudinally along a first direction (Di) and transversely along a second direction (D2), the acoustic panel (1000) further comprising an acoustic component (200) disposed between the acoustic skin (100) and the closing skin (300), the acoustic component (200) comprising a plurality of partitions (210) extending along a third direction (D3) perpendicular to the first and second directions (DB D2) between a lower end (210b) and an upper end (210a), the lower ends (210b) of the partitions (210) being in contact with the closing skin (300), the acoustic panel (1000) defining a plurality of acoustic cells (1) delimited along the second direction (D2) by two consecutive partitions (210) of the acoustic component (200),the acoustic panel (1000) further comprising a plurality of hollow acoustic elements (220) arranged in the acoustic cells (1), the acoustic panel (1000) being characterized in that each hollow acoustic element (220) comprises a first edge (221) and a second edge (222) each extending in a plane defined by the first and second directions (DB D2) from the upper end (210a) of the partitions (210) of one of the cells (1), and in that each hollow acoustic element (220) comprises a third edge (223) extending from a distal end of the first edge (221) and a fourth edge (221) extending from a distal end of the second edge (222), the third and fourth edges (223, 224) extending in the direction of the closing skin (300) to a free end.

2. Acoustic panel (1000) according to claim 1, wherein the plurality of partitions (210) of the acoustic component (200) comprises first partitions (211) extending lengthwise along the first direction (DJ) and second partitions (212) extending lengthwise along the second direction (D2), the acoustic cells (220) being delimited along the first direction (Di) by two consecutive second partitions (212) of the acoustic component (200).

3. Acoustic panel (1000) according to claim 2, wherein the first, second, third and fourth edges (221, 222, 223, 224) of the hollow acoustic elements (220) extend along the first direction (DJ) from one of the second partitions (212) of the acoustic component (200) to the second consecutive partition (212).

4. Acoustic panel (1000) according to any one of claims 1 to 3, the acoustic panel (1000) further comprising support elements (230) extending along the third direction (D3) from the upper edges (210a) of the partitions (210) of the acoustic component (200) to the acoustic skin (100) so as to keep the acoustic skin (100) away from the acoustic elements (220).

5. Acoustic panel (2000) according to any one of claims 1 to 4, the acoustic panel (100) further comprising an interposition layer (400) disposed between the acoustic elements (220) and the acoustic skin (100).

6. Acoustic panel (2000) according to claim 5, wherein the interposition layer (400) is a wire mesh, lattice or woven fibrous texture.

7. Acoustic panel (1000) according to any one of claims 1 to 6, wherein, for at least a portion of the hollow acoustic elements (220; 520), the distance (Wn; W4[ ) along the second direction (D2) between the distal ends of the first edge and the second edge (221, 222; 521, 522) is greater than or equal to the distance (W[2; W42) along the second direction (D2) between the free ends of the third edge and the fourth edge (223, 224; 523, 524).

8. Acoustic panel (1000) according to any one of claims 1 to 7, wherein, for at least a portion of the hollow acoustic elements (320; 420), the distance (W2 i; W31) along the second direction (D2) between the distal ends of the first edge and the second edge (321, 322; 421, 422) is less than or equal to the distance (W2 2; W3 2) along the second direction (D2 ) between the free ends of the third edge and the fourth edge (323, 324; 423, 424).

9. Acoustic panel (1000) according to any one of claims 1 to 8, wherein the third and fourth edges (423, 424; 523, 524) of at least a portion of the hollow acoustic elements (420; 520) are curved.

10. Acoustic panel according to any one of claims 1 to 9, wherein the third and fourth edges (223, 224; 323, 324) of at least a portion of the hollow acoustic elements (220; 320) are straight.

11. Acoustic panel according to any one of claims 1 to 10, wherein a first part (PJ) of the acoustic cells (3, 4) of the acoustic component (200bis) has a first height (Lpi) along the third direction (D3) and a second part (P2) of the acoustic cells (3, 4) of the acoustic component (200bis) has a second height (LP2) along the third direction (D3) different from the first height (LPi).

12. Acoustic panel according to any one of claims 1 to 11, wherein a first part of the acoustic cells (3) of the acoustic component (200bis) comprises third and fourth edges having a first shape and a second part of the acoustic cells (4) of the acoustic component (200bis) comprises third and fourth edges having a second shape different from the first shape.

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