Method for manufacturing an acoustic panel having a capsular skin, and acoustic panel incorporating such a skin

Abstract

An acoustic panel comprising a cellular structure, such as a honeycomb structure, having cells that open at least onto a first frontal face of the structure. The panel comprises a capsular skin which is fastened to the first frontal face of the cellular structure next to a plurality of cells. The capsular skin including a continuous layer of material, in one piece, forming capsules that extend into the cellular structure. At least one channel is provided at the apex of each capsule for the passage of acoustic waves. Such a panel effectively attenuates the noise of aircraft engines, in particular, the low frequencies. It is extremely easy to manufacture industrially, the capsular skin being able to be obtained by molding with polymerization in situ, the polymerizable material then adhering to the cellular structure while it polymerizes.

Claims

1. An acoustic panel comprising: a cellular structure having a first frontal face and a second frontal face, between which there extend cells, said cells opening at least onto the first frontal face of the structure, a capsular skin fastened to the first frontal face of the cellular structure next to a plurality of cells of said cellular structure, said capsular skin comprising a continuous layer of material, in one piece, forming capsules that extend into the cellular structure, wherein the continuous layer of material comprises mutually independent wire cloth elements in an upper part of each capsule and does not have polymerizable material at the apex of the capsules, wherein the capsular skin incorporates a channel in a vicinity of the apex of each capsule formed by one or more meshes of the wire cloth elements, the capsular skin not having wire cloth away from the upper parts of the capsules, and a resistive skin fastened to the capsular skin, the capsular skin being obtained by molding the layer of material which includes a polymerizable material away from the apex in a mold comprising a plate and a plurality of raised elements connected to and protruding from the plate, each of the raised elements having a shape of the capsules, and the mold being provided with the layer of material arranged on the first frontal face of the cellular structure before the material is polymerized, the polymerization taking place in situ, wherein the capsular skin adheres directly to the first frontal face of the cellular structure.

2. The acoustic panel according to claim 1, wherein the at least one channel is a communication tube at the apex of each capsule.

3. A method for manufacturing an acoustic panel, comprising: providing a cellular structure having a first frontal face and a second frontal face, between which there extend cells, said cells opening at least onto the first frontal face of the structure, fastening a capsular skin to the first frontal face of the cellular structure next to a plurality of cells of said cellular structure, said capsular skin comprising a continuous layer of material, in one piece, forming capsules that extend into the cellular structure, providing at least one channel in a vicinity of an apex of each capsule for passage of acoustic waves, wherein the continuous layer of material comprises mutually independent wire cloth elements in an upper part of each capsule and does not have polymerizable material at the apex of the capsules formed by one or more meshes of the wire cloth element, the capsular skin not having wire cloth away from the upper parts of the capsules, obtaining the capsular skin, after forming the capsules, by molding the layer of material which includes a polymerizable material away from the apex in a mold comprising a plate having a plurality of raised elements connected to and protruding from the plate, each of the raised elements having a shape of the capsules, the polymerizable material being deposited on the mold, and arranging the mold on the first frontal face of the cellular structure, inserting each raised element into a cell of the cellular structure before the polarizable material of the layer of material is polymerized, and polymerizing the material in situ.

4. The method according to claim 3, including a step of withdrawing the mold after the material is polymerized, the layer of polymerized polymerizable material forming a capsular skin that adheres to the first frontal face of the cellular structure and forms capsules in the cells.

5. The method according to claim 3, further including a step of manufacturing the cellular structure in a flat state, and using a mold having a flat plate for the capsular skin, using a polymerizable material that maintains, after polymerization, sufficient flexibility to allow an assembly made up of the cellular structure and the capsular skin to deform, and shaping the assembly so as to give the panel a desired shape.

6. The method according to claim 3, wherein the polymerizable material is chosen from thermoplastic materials, elastomers, polyurethanes and epoxy resins.

7. The method according to claim 3, wherein the step of polymerizing comprises a step of heating at a temperature that is sufficiently low for the cellular structure not to be damaged.

8. An aircraft nacelle comprising acoustic panels according to claim 1.

9. An aircraft propulsion unit, comprising a nacelle according to claim 8.

10. An aircraft comprising at least one propulsion unit according to claim 9.

11. The method according to claim 3, wherein the resistive skin includes sound-absorbing holes in the form of micro-perforations.

12. The acoustic panel according to claim 1, wherein the resistive skin includes sound-absorbing holes in the form of micro-perforations.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention, according to one exemplary embodiment, will be understood better and the advantages thereof will become more clearly apparent from reading the following detailed description, which is given by way of entirely non-limiting illustration, with reference to the appended drawings, in which:

(2) FIG. 1 is a perspective view of an aircraft of the prior art, but which can be equipped with acoustic panels according to the invention.

(3) FIG. 2 is an exploded perspective view of an air intake of an aircraft nacelle of the prior art, but which can be equipped with acoustic panels according to the invention.

(4) FIG. 3 is a view in cross section of a portion of a mold and of a cellular structure for manufacturing an acoustic panel according to the invention, at different stages of this manufacture.

(5) FIG. 4 is a view in cross section of a portion of an acoustic panel according to the invention.

(6) FIG. 5 is a view in cross section of a portion of a mold for manufacturing a capsular skin according to the invention.

(7) FIG. 6 is a view in cross section of a portion of another mold for manufacturing a capsular skin according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) FIG. 1 shows a two-engine aircraft, the two nacelles 200 of which have an air intake that is able to be equipped with panels according to the invention.

(9) An aircraft nacelle air intake, such as the one illustrated in the appended FIG. 2, usually comprises structural elements such as a front frame 101 and a rear frame 104, and, from the front to the rear of the nacelle, a lip 100 carried by the front frame 101, external panels 102 that continue the lip on the outside of the nacelle, internal panels 103 that continue the lip on the inside of the nacelle and delimit an interior duct for channeling the air in the direction of the engine, the external panels 102 and internal panels 103 being supported by the front frame 101 and the rear frame 104.

(10) The invention proposes novel acoustic panels that can be used as internal panels 103 in a conventional air intake such as the one illustrated in FIG. 2. The invention also proposes a simple industrial method for manufacturing these panels. FIGS. 3 and 4 illustrate the different steps in a preferred embodiment of this method.

(11) The method according to the invention comprises the provision of a cellular structure 2 (see FIG. 3), which has cells 21 that extend transversely between a first frontal face 22 and a second frontal face 23. In the example illustrated, these cells open onto both the frontal faces of the structure. To produce the invention, it is sufficient, however, for the cells to open onto one of the frontal faces, known as the first frontal face.

(12) Preferably, this cellular structure 2 is a honeycomb structure, made of synthetic fibers known under the trade name Nomex?. This material, which is well known to a person skilled in the art, is easily deformable (compressible, extensible and able to be curved) in a direction W; it is more rigid in a direction Y (orthogonal to W) while remaining able to be curved in this direction.

(13) According to a preferred embodiment of the invention, use is also made of a mold 60 comprising a plate 62 which, in this case, is flat, and a plurality of raised elements 61 protruding from this plate.

(14) A layer of polymerizable material 33 is deposited on the mold 60, this material being able to be a thermoplastic or an elastomer, in particular, a polyurethane.

(15) While the polymerizable material is still fresh, the mold is turned over and pressed against the first frontal face 22 of the cellular (honeycomb) structure 2, each raised element 61 of the mold being inserted into a cell 21 of the structure.

(16) The whole is cured at a low temperature, the curing temperature needing to allow the polymerization of the layer of polymerizable material 33 without deforming or damaging the cellular structure.

(17) The mold is then removed, the layer of polymerized polymerizable material 33 forming a capsular skin 3 that adheres to the first frontal face 22 of the cellular structure and forms capsules 31 in the cells 21 of the cellular structure. The capsular skin 3 can be seen in the right-hand part of FIG. 3. Each capsule 31 thus divides a cell 21 into two acoustic pockets 34, 35 intended to damp waves of different frequencies, one of the acoustic pockets forming a ? wave resonator while the other acoustic pocket forms a Helmholtz resonator.

(18) Holes are then pierced at the apex of the capsules 31 by any appropriate means in order to create channels 32 for the passage of acoustic waves between the two acoustic pockets of the cells.

(19) Throughout the description, an apex of a capsule is understood as being the point of the capsule that is furthest away from the first frontal face of the cellular structure. If the end of the capsule that extends inside the cell is a flat face parallel to the first frontal face of the cellular structure as illustrated in the appended figures, the apex corresponds to the central point of this flat face and the channel can be provided at any location in this flat face, preferably at the middle (that is to say, exactly at the apex) but not necessarily (i.e., in the vicinity of the apex). If the end of the capsule that is situated inside the cell is not a flat surface but, for example, a spherical cap, the apex is the central peak of this cap, and the channel can be provided at this peak (that is to say, exactly at the apex) or in the vicinity of the apex, for example at any point on the spherical cap forming the end of the capsule.

(20) In a preferred (but optional) version, in order to terminate the acoustic panel according to the invention, a resistive skin 4, which is perforated or micro-perforated with sound-absorption holes 41, and an intact structural skin 5 are fastened, by adhesive bonding or by ultrasonic welding, to an assembly made up of the cellular structure and the capsular skin 3.

(21) As shown in FIG. 3, the capsular skin 3 incorporates a woven element 24 in the upper part of each capsule 31 and does not have polymerizable material at the apex of the capsules and in the vicinity of the apex; the channel 32 or channels provided at the apex of each capsule are then formed by one or more meshes of the woven element. The woven elements 24 are preferably made of wire cloth, for example made of titanium, stainless steel or the like. The woven elements 24 may be parts of a woven layer 25 that extends over the entire surface of the capsular skin 3 or mutually independent elements, the capsular skin then not having cloth away from the upper parts of the capsules 31.

(22) In the example illustrated in FIG. 4, the resistive skin 4 is positioned at the first face 22 of the cellular structure, against the capsular skin 3, while the structural skin 5 is positioned against the second frontal face 23 of the cellular structure. The opposite is also possible. It should be noted that, for the sake of clarity, a small space has been left in the drawing between the skins 3 and 4; this space no longer exists once the skin 4 has been fastened to the skin 3. In the same way, the skin 5 appears to be detached from the cellular structure 2 in the drawing, this not being the case in the finished panel.

(23) The distances between the apex of a capsule and the frontal faces of the cellular structure depend on the acoustic frequencies intended to be damped, the objective being to cover a range of low frequencies and a range of high frequencies by combining a ? wave resonator (the pocket of which has a height of several tens of mm) and a Helmholtz resonator (volume in mm3).

(24) Depending on its destination, the panel needs to have one or more curves in one or more directions. In the case of an air intake internal panel (such as the panels 103 in FIG. 2), the desired shape for the panel is curved in the axial direction X of the air intake (meaning that a cross section of the panel through a plane comprising the central axis X of the air intake is a curved line); the panel is also curved in the transverse direction Y of the air intake or in the direction Z of gravity (in this case, a cross section of the panel through any plane YZ orthogonal to the central axis X of the air intake is preferably a circular arc). The panel therefore needs to be shaped.

(25) Preferably, forming for obtaining the curve(s) of the panel takes place in the final part of the method for the manufacture thereof, after the production and assembly of the capsular skin 3 and the cellular structure 2. In this case, as illustrated in FIG. 3, use is made of a mold 60 (or the mold 70 or 80 in FIGS. 5 and 6), the plate 62 (or 72 or 82) of which is flat, and the assembly made up of the cellular structure 2 and the capsular skin 3 is flat. The forming can then be carried out, before or after the resistive skin 4 and structural skin 5 have been fastened. This forming is easier if the capsular skin 3 has been polymerized in situ as explained above, with a polymer material that maintains relative flexibility after polymerization.

(26) In a variant, the resistive skin 4 and structural skin 5, for the one part, and the assembly made up of the cellular structure 2 and the capsular skin 3, for the other part, are formed before the skins are fastened to the assembly. In this case, the cellular structure and the capsular skin themselves can even be individually formed before being assembled. Such a method requires a high degree of precision, however, and appears to be more complex to implement.

(27) FIG. 5 shows a mold 70 having a flat plate 72 and in which the raised elements 71 forming the capsules are surmounted by a conical tip 73 on which the polymerizable material is not deposited or held. After demolding, each conical tip 73 leaves a hole in the capsular skin at the apex of each capsule, for the passage of acoustic waves between the two acoustic pockets of the cell 21. The mold 80 in FIG. 6 comprises, at the apex of each of these raised elements, not just a conical tip 84, the function of which is the same as the tip 73 of the mold in FIG. 5, but also a cylindrical peg of circular section 83 on which polymerizable material is deposited and which makes it possible to obtain, after polymerization, at the apex of each capsule, a communication tube between the two acoustic pockets 34, 35, the tube forming a Helmholtz resonator with the pocket 35.

(28) The invention extends to all the variants within the competence of a person skilled in the art that are covered by the scope of the appended claims.

(29) While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.