FR2912780A1 - Acoustic lining i.e. acoustic panel, for nacelle of aircraft, has series of longitudinal bands intersecting series of transversal bands so as to delimit duct between two adjacent longitudinal bands and two adjacent transversal bands - Google Patents

Abstract

The lining has a honeycomb structure (30) delimited by imaginary surfaces (34, 36) on which a reflective layer and an acoustic resistive porous layer are respectively fixed. The structure has a set of ducts emerging at the level of the imaginary surfaces. The structure has a series of longitudinal bands (38) and a series of transversal bands (40) that are spaced from each other and not intersected with each other. The longitudinal bands intersect the transversal bands so as to delimit a duct between two adjacent longitudinal bands and two adjacent transversal bands. An independent claim is also included for a method of forming a lining for acoustic treatment.

Description

COATING FOR ACOUSTIC TREATMENT INCORPORATING A STRUCTURE

ALVEOLAIRE WITH A COMPLEX SHAPE

  The present invention relates to a coating for acoustic treatment incorporating a honeycomb structure with a complex shape, said coating being more particularly adapted to cover a leading edge of an aircraft, in particular an air inlet of a nacelle.

  To limit the impact of noise pollution near airports, international standards are becoming more stringent in terms of noise emissions. Techniques have been developed for reducing the noise emitted by an aircraft, and in particular the noise emitted by a propulsion unit, by arranging, at the level of the walls of the ducts, coatings intended to absorb a part of the sound energy, in particular by using the principle of Helmholtz resonators. In known manner, a coating for acoustic treatment, also called acoustic panel, comprises from the outside to the inside an acoustically resistive porous layer, at least one cellular structure and a reflective or impermeable layer. By layer is meant one or more layers of the same nature or not. The acoustically resistive porous layer is a porous structure having a dissipative role, partially transforming the acoustic energy of the sound wave passing through it into heat. It includes so-called open areas capable of passing acoustic waves and other so-called closed or full not allowing sound waves to pass but designed to ensure the mechanical strength of said layer. This acoustically resistive layer is characterized in particular by an open surface area which varies essentially according to the engine, the components constituting said layer. The honeycomb structure is delimited by a first imaginary surface at which the acoustically resistive porous layer is directly or indirectly reportable and by a second imaginary surface at which the reflective layer can be directly or indirectly reported. and comprises a plurality of ducts opening on the one hand at the first surface and secondly on the second surface. These ducts are closed by the acoustically resistive porous layer on the one hand and the reflective layer on the other hand so as to form a cell. A honeycomb structure is used to form the honeycomb structure of a coating for acoustic treatment. Different types of materials can be used to form the honeycomb.

  According to one embodiment, a honeycomb is obtained from strips disposed in a vertical plane extending in a first direction, each strip being alternately connected to the adjacent strips with a spacing between each bonding zone. Thus, when all the assembled strips are expanded in a direction perpendicular to the first direction, a honeycomb panel is obtained, the strips forming the side walls of the hexagonal section ducts. This structure makes it possible to obtain high mechanical strengths during compression and bending. In the case of a coating for acoustic treatment, the complex is made flat, namely the acoustically resistive and reflective porous layers are connected to the cellular structure in a planar configuration. Subsequently, the complex is shaped at the surface to be treated. In the case of a flat wall or a cylindrical wall of a nacelle of large diameter, this shaping can be performed. It is different for small diameter pipes or complex surfaces, for example with two radii of curvature as an air inlet of a nacelle. These difficulties of formatting derive first and foremost from the very nature of the cellular panel which has a high resistance to bending. Thus, when the honeycomb structure is curved according to a first radius of curvature oriented upwards and disposed in a first plane, this tends to cause a radius of curvature oriented downwards and arranged in a plane substantially perpendicular to the first, the honeycomb structure in the form of a horse saddle or a hyperbolic paraboloid.

  These difficulties of formatting also arise from the nature of the connection between the honeycomb structure and the layers which is not elastic. Thus, the honeycomb being made flat under stress, its shaping weakens it. In all cases, the shaping of the complex used as a coating for the acoustic treatment requires complex and expensive tools and requires a long cycle time. According to another problem, even if it was possible to bend the complex, the existing solution would not be satisfactory because the shaping causes random deformation of the side walls of the ducts of the honeycomb structure so that it is difficult to determine the positioning said side walls of the ducts, the latter being hidden by the reflective and acoustically resistive layers. Given the difficulties in shaping the complex, the extent of acoustically treated surfaces is limited inside the ducts of the nacelle, said treated surfaces not extending at the lip of the entrance of the nacelle. air of a nacelle. Also, the present invention aims at overcoming the drawbacks of the prior art, by proposing a coating for the acoustic treatment incorporating a honeycomb structure enabling said coating to be shaped according to a complex surface without altering its mechanical characteristics, said coating having simple design and manufacturing costs adapted to the market. To this end, the invention ob ob jet a coating for acoustic treatment reported at a surface of an aircraft, particularly at a leading edge such as an air inlet of a nacelle of aircraft, said coating comprising a honeycomb structure delimited on the one hand by a first imaginary surface on which a reflective layer is attached, and on the other hand by a second imaginary surface on which is reported an acoustically resistive porous layer, said structure honeycomb comprising a plurality of ducts opening on the one hand at the first imaginary surface, and secondly on the second imaginary surface, characterized in that the honeycomb structure comprises a series of first non-intersecting bands between them and spaced apart from each other, and at least a second series of second non-intersecting strips spaced apart and in that the first strips are s with the second strips so as to delimit a duct between two adjacent first strips and second two adjacent strips. Other features and advantages will become apparent from the following description of the invention, a description given by way of example only, with reference to the appended drawings in which: FIG. 1 is a perspective view of a propulsion unit FIG. 2 is a longitudinal section illustrating an air inlet of a nacelle comprising a coating for the acoustic treatment according to the invention, FIG. 3 is an elevational view illustrating a longitudinal strip arranged. in a radial plane; FIG. 4A is an elevational view illustrating a first transverse band disposed along a first secant surface at radial planes; FIG. 4B is a perspective view illustrating the first band illustrated in FIG. 4A; FIG. 5A is an elevational view illustrating a second transverse strip disposed along a second secant surface at radial planes, said second surface following the portion s Figure 5B is a perspective view illustrating the second band illustrated in Figure 5A which can be bent to interlock in the first bands, Figure 6B is a perspective view illustrating the second band illustrated in Figure 5A which can be bent to interlock in the first bands; a perspective view illustrating a honeycomb structure according to the invention adapted to be adapted to an angular sector of an air inlet, and FIG. 7 is a perspective view illustrating in detail the connection between a longitudinal strip and a transverse band. The present invention is now described applied to an air intake of a propulsion unit of an aircraft. However, it can be applied to the different leading edges of an aircraft or to the different surfaces of an aircraft at which an acoustic treatment is performed. FIG. 1 shows a propulsion unit 10 of an aircraft connected under the wing by means of a mast 12. However, this propulsion unit could be connected to other zones of the aircraft.

  This propulsion unit comprises a nacelle 14 in which is disposed in a substantially concentric manner an engine driving a fan mounted on its shaft 16. The longitudinal axis of the nacelle is referenced 18.

  The nacelle 14 comprises an inner wall 20 delimiting a duct with an air inlet 22 at the front, a first part of the incoming air flow, called primary flow, passing through the engine to participate in the combustion, the second part of the air flow, called secondary flow, being driven by the fan and flowing in an annular conduit defined by the inner wall 20 of the nacelle and the outer wall of the engine. The upper part 24 of the air inlet 22 describes a substantially circular shape which extends in a plane which may be substantially perpendicular to the longitudinal axis 18, as shown in FIG. 2, or not perpendicular, with the portion summit at 12 o'clock slightly advanced. However, other forms of air intake can be envisaged. For the rest of the description, aerodynamic surface means the envelope of the aircraft in contact with the aerodynamic flow. To limit the impact of nuisances, a coating 26 to absorb some of the sound energy, including using the principle of Helmholtz resonators is provided in particular at the aerodynamic surfaces. In known manner, this acoustic coating, also called acoustic panel, comprises from inside to outside a reflective layer 28, a honeycomb structure 30 and an acoustically resistive layer 32.

  Alternatively, the acoustic coating may comprise a plurality of cellular structures 30 separated by acoustically resistive layers called septum. By layer is meant one or more layers of the same nature or not. According to one embodiment, the reflective layer 28 may be in the form of a metal sheet or a skin consisting of at least one layer of woven or non-woven fibers embedded in a resin matrix. The acoustically resistive layer 32 may be in the form of at least one layer of woven or non-woven fibers, the fibers preferably being coated with a resin to ensure the recovery of forces in the different directions of the fibers. According to another embodiment, the acoustically resistive structure 32 comprises at least one porous layer in the form of, for example, a metallic or non-metallic fabric such as a Wiremesh and at least one structural layer, for example a metal or composite sheet with oblong holes or microperforations. The reflective layer and the acoustically resistive layer are not more detailed because they are known to those skilled in the art.

  The honeycomb structure 30 corresponds to a volume defined on the one hand by a first imaginary surface 34 on which the reflective layer 28 is attached, and on the other hand by a second imaginary surface 36 on which the acoustically resistive layer 32 is attached, such as illustrated in Figure 6.

  The distance between the first imaginary surface 34 and the second imaginary surface 36 may not be constant. Thus this distance may be greater at the lip of the air inlet to give said structure a greater resistance including compression. The honeycomb structure 30 comprises on the one hand a plurality of first strips 38 called longitudinal strips corresponding to the intersection of the volume with radial planes incorporating the longitudinal axis 18, and secondly, a plurality of second bands 40 called strips. cross-sections corresponding to the intersection of the volume with secant surfaces at radial planes. Preferably, at each point of intersection with the second imaginary surface 36, each transverse strip 40 is substantially perpendicular to the tangent to the second imaginary surface 36 at the considered point. Preferably, at each point of intersection with the transverse bands 40, each longitudinal band 38 is substantially perpendicular to the tangent of each transverse strip 40 at the point in question. Secant surface means a plane or surface that is intersecting with the first imaginary surface 34 and the second imaginary surface 36.

  More generally, the honeycomb structure comprises a series of first strips 38 disposed at intersecting surfaces, said first strips 38 being non-intersecting and spaced apart from each other, and at least a second series of second strips 40 arranged at the level of intersecting surfaces, said second strips 40 being non-intersecting and spaced apart from each other. The first bands 38 are intersecting with the second bands so as to delimit a duct between two adjacent first strips and second two adjacent strips. We can envisage more than two series of bands. However, in order to simplify the design, two sets of 15 bands are chosen. Thus, ducts with four side faces are obtained. Similarly, to simplify the design, we will have the first bands in radial planes containing the longitudinal axis of the nacelle. To obtain a more rigid structure, the second strips will be arranged so that they are substantially perpendicular to the first strips 20 in order to obtain ducts with square, rectangular sections. This solution also simplifies the design. However, one could consider other forms of section, for example rhombus. At the level of the curved zones, the sections of the conduits are evolutionary. Thus, they vary between a large section at the second imaginary surface 36 and a smaller section at the first imaginary surface 34.

  To assemble the bands of the different intersecting series, first cutouts 42 are provided at the level of the longitudinal strips 38 which cooperate with second cuts 44 at the level of the transverse strips 40. The first and second cuts 42 and 44 do not extend. not from one edge to another to facilitate assembly. The length of the first blanks 42 and the second blanks 44 are adjusted so that the edges of the longitudinal and transverse strips are arranged at the imaginary surfaces 34 and 36. According to one embodiment, the first blanks 42 extend. from the edge of the longitudinal strips disposed at the second imaginary surface 36. In addition, the second cutouts 44 extend from the edge of the transverse strips disposed at the first imaginary surface 34. According to one embodiment, the shape of the alveolar structure 30 that it will have when it is in place at the level of the surface to be treated is digitized. The longitudinal and transverse strips are then positioned virtually in order to define for each of them their geometries. We can discretize the surface using the same method as the mesh software. The surface is discretized by projection of the geometries.

  Thus, as illustrated in FIG. 3, in the case of an air intake, the longitudinal strips 38 have a C shape with a first edge 46 likely to correspond with the first imaginary surface 34 and a second edge 48 capable of correspond to the second imaginary surface 36. According to the variants, the distance between the edges 46 and 48 may vary from one band to another or along the profile of the same band. The longitudinal strips 38 are cut in substantially flat plates. This flat cut simplifies manufacturing. Moreover, the shapes of the imaginary surfaces 34 and 36 are derived from the shapes of the edges 46 and 48 which are generated by cutting and not by deformation which guarantees a greater dimensional accuracy of said imaginary surfaces. Insofar as the longitudinal strips 38 are arranged in radial planes, they are not curved during assembly with the transverse strips 40. As illustrated in FIGS. 4A, 4B, 5A and 5B, in the case of In one air inlet, the transverse strips 40 have ring shapes with a first edge 50 capable of corresponding with the first imaginary surface 34 and a second edge 52 capable of corresponding with the second imaginary surface 36. The edges 50 and 52 have a radius of curvature that can vary progressively as a function of the distance from the top portion 24, from a value R substantially corresponding to the radius of curvature of the duct forming the nacelle for the transverse strips 40, as illustrated in FIG. 4A, and an infinite radius, the edges 50 and 52 being substantially rectilinear, for the transverse band 40 disposed at the top portion 24 of the air inlet, as illustrated in FIG. 5A. The transverse strips 40 are cut in substantially flat plates. An advantage of the invention lies in the fact that the transverse and longitudinal strips are cut flat which contributes to simplification of manufacture and they do not undergo any forming operation which guarantees the adjustment of the cells on the reflective layer. and the acoustically resistive layer. The transverse bands, depending on their position, are sufficiently flexible to be optionally curved so as to nest in the longitudinal strips. As illustrated in Figure 4B, the transverse strips 40 disposed in areas of the honeycomb structure having a single radius of curvature, including substantially cylindrical portions, are arranged in planes once assembled.

  Most of the transverse strips 40 are sufficiently flexible to be optionally curved along a radius of curvature r perpendicular to the surface of the strips, as shown in FIG. 5B, as a function of their position at the level of the cellular structure. Thus, the transverse bands 40 remote from the summit portion 24 are not curved, which corresponds to a radius of curvature r infinite, the transverse strips 40 having a radius of curvature r which decreases gradually depending on the distance separating the transverse band considered from the top portion 24 to a radius r substantially equal to the radius of the top portion for the transverse strip 40, shown in Figures 5A and 5B, disposed at the top portion 24. According to a significant advantage of the In the invention, the strips are no longer deformed once assembled or when the reflective or acoustically resistive layers are put in place. The acoustic coating thus formed having shapes adapted to those of the surface to be treated, it is no longer deformed when it is placed at the level of said surface to be treated. Therefore, unlike the prior art, the connection between the honeycomb structure and the reflective layer or the acoustically resistive layer is no longer likely to be damaged and the position of the walls of the ducts that correspond to the strips is perfectly known and corresponds to the desired position when scanning. According to one embodiment, the strips 38 and 40 may be made of cardboard, metal (titanium, aluminum alloy steel), composite (glass fibers for example). The materials used can be mixed, for example using glass fibers for the longitudinal strips and titanium for the transverse strips. Advantageously, the metal will be chosen to give the structure good impact resistance, in particular impact to the bird. According to the variants, the assembly of the strips can be manual or robotic.

  As illustrated in FIG. 7, the longitudinal strips 38 and the transverse strips 40 are assembled and then joined together by welding, for example a solder 54, or by gluing. However, other solutions to provide a link between the bands can be envisaged.

  According to one advantage of the invention, it is possible to vary the thickness of the honeycomb structure. Thus, the portions of the honeycomb structure disposed in line with the lip have a thickness greater than the parts of the honeycomb structure remote from said lip. According to the variants, the edges of the strips may have more complex shapes and comprise several radii of curvature in order to obtain more complex surfaces. Depending on the case, it is possible to vary the spacing between the bands of the same series. Thus, the first consecutive cutouts 42 'and 42 "may have a smaller gap to obtain a small gap between the consecutive transverse strips 40' and 40" as shown in FIG. 6. Likewise, the second cutouts 44 ' and 44 "consecutive may have a smaller gap to obtain a small gap between the longitudinal strips 38, 38" consecutive as shown in Figure 6. This arrangement provides cells with variable sections. According to another improvement, the strips 38 and 40 may comprise cutouts 56 for making certain cells communicate with each other and obtain a network of conduits. This solution makes it possible to generate a network of ducts, provided between the closely spaced adjacent strips 38 and 40, used to convey hot air and to obtain the frost treatment function. The non-communicating cells are used for the function of the acoustic treatment.

  This configuration makes it possible to make the functions of frost treatment and acoustic treatment compatible, some cells of the cladding, those which do not communicate with each other, being intended exclusively for acoustic treatment and others which communicate with each other exclusively for the purpose of acoustic treatment. Frost treatment.

Claims (8)

  A coating for acoustic treatment reported at the level of a surface of an aircraft, in particular at a leading edge such as an air intake of an aircraft nacelle, said coating comprising at least one cellular structure (30) bounded on the one hand by a first imaginary surface (34) to which a reflective layer (28) is attached, and on the other hand by a second imaginary surface (36) to which is attached an acoustically porous layer resistive device (32), said cellular structure (30) comprising a plurality of conduits opening on the one hand at the first imaginary surface (34), and secondly on the second imaginary surface (36), characterized in that the honeycomb structure (30) comprises a series of first strips (38) which are non-intersecting and spaced apart from one another, and at least one second series of second strips (40) which are non-intersecting and spaced apart from one another and that first strips (38) are intersecting with the second strips (40) so as to delimit a duct between two adjacent first strips (38) and two adjacent second strips (40).   2. Coating for acoustic treatment according to claim 1, disposed at an air inlet of an aircraft nacelle, characterized in that the first so-called longitudinal strips are arranged in radial planes containing the longitudinal axis. (18) of the nacelle.   3. coating for acoustic treatment according to claim 1 or 2, characterized in that each second strip (40) said transverse strip is substantially perpendicular to the tangent to the second imaginary surface (36).   4. Coating for acoustic treatment according to claims 2 and 3, characterized in that each longitudinal strip (38) is substantially perpendicular to the tangent of each transverse strip (40).   5. Coating for acoustic treatment according to any one of the preceding claims, characterized in that the longitudinal strips (38) comprise first cutouts (42) which cooperate with second cutouts (44) provided at the level of the transverse strips (40). ).   6. Coating for acoustic treatment according to any one of the preceding claims, characterized in that the first so-called longitudinal strips (38) and the second so-called transverse strips (40) comprise cutouts or orifices (56) for communicating certain conduits. between them so as to obtain a network of ducts provided for the treatment of frost, the non-communicating ducts being provided for the acoustic treatment.   An aircraft nacelle incorporating a coating for acoustic treatment according to any one of the preceding claims.   8. A method of producing a coating for acoustic treatment reported at the level of a surface to be treated of an aircraft, particularly at a leading edge such as an air inlet of a nacelle. aircraft, said coating for acoustic treatment having from inside to outside a reflective layer (28), a honeycomb structure (30) and an acoustically resistive layer (32), characterized in that it consists in: - digitizing the shape of the honeycomb structure (30) it will have when it is placed at the level of the surface to be treated, - virtual position to define their geometries, a first series of first strips (38) no intersecting between them and spaced apart from each other, and at least a second series of second strips (40) non-intersecting and spaced apart from each other, the first strips (38) being decanting with the second strips (40) so as to delimit a duct on the one hand, two adjacent first bands (38) and on the other hand two adjacent second strips (40), -cutting each strip (38, 40) according to their previously defined geometries, -assembling the strips (38, 40) in order to obtain a honeycomb structure having shapes adapted to the surface to be treated, and - to set up the reflective layer (28) and the acoustically resistive layer (32).