Panel for acoustic treatment comprising a junction between two parts and process for the reparation of a panel for acoustic treatment

An acoustic treatment panel includes two portions with edges spaced in one direction, and from the outside to the inside, a first acoustically resistive layer, a first alveolar structure, and a reflective layer, and a block inserted between the two edges which includes, from the outside to the inside, a second acoustically resistive layer arranged at the first acoustically resistive layer and a second alveolar structure. The block includes at least one sector of alveolar structures with sloped pipes whose height is less than that of the first alveolar structure, whereby the pipes are sloped in a direction such that the ends of the pipes are close to one of the edges of the portions at the first acoustically resistive layer, and the opposite ends of the pipes are moved away from the edge and the reflective layer so as to house connecting elements between the block and the panel.

This invention relates to an acoustic treatment panel that comprises a junction, whereby said panel is more particularly designed to be placed at a wall of an aircraft nacelle. The invention also relates to a process for repair of an acoustic treatment panel.

The noise that is emitted by an aircraft propulsion system consists of, on the one hand, jet noise, produced outside of the pipes as a result of the mixing of various air flows and exhaust gases, and, on the other hand, noise generated by the inside parts, so-called internal noise, produced by the fan, the compressors, the turbines and the combustion that propagates inside the pipes.

To limit the impact of noise pollution close to airports, the international standards are increasingly restrictive as far as sound emissions are concerned.

Techniques have been developed for reducing the internal noise, in particular by arranging, at pipe walls, panels or coverings that are intended to absorb a portion of the sound energy, in particular by using the principle of quarter-wave resonators.

In a known manner, as illustrated inFIG. 1, an acoustic treatment panel, also called an acoustic panel or covering, comprises—from the outside to the inside—an acoustically resistive structure10, an alveolar structure12, and a reflective layer14.

Layer is defined as one or more layers that may or may not be of the same type.

According to one embodiment, the reflective layer14can be a non-perforated sheet or plate that is made of metal or composite material.

The alveolar structure12can comprise a large number of juxtaposed cavities, blocked at one end by the reflective layer14and partially blocked at the other end by the acoustically resistive layer10. The cavities of the alveolar structure are delimited by walls that are perpendicular to the reflective layer14or to the acoustically resistive layer10, whose ends are bonded against said reflective layer14and the acoustically resistive layer10.

According to one embodiment, the alveolar structure12comes in the form of a honeycomb that is made of metal or composite material.

The acoustically resistive structure10is a porous structure that plays a dissipative role, partially transforming the acoustic energy of the sound wave that passes through it into heat. It comprises so-called open zones that are able to allow acoustic waves to pass and other so-called closed or flat zones that do not allow the sound waves to pass but are designed to ensure the mechanical strength of said layer. This acoustically resistive layer is characterized in particular by an open surface ratio that varies essentially based on the engine, with components constituting said layer.

To cover a surface such as an air intake of an aircraft nacelle, several acoustic treatment panels can be juxtaposed and connected by splice plates. These splice plates do not have an acoustic function and should have an adequate width for obtaining a structure that has adequate mechanical characteristics. This assembly method does not make it possible to obtain an optimized acoustic treatment to the extent that the open surface ratio is not homogeneous over the entire surface because of the presence of splice plates.

To optimize the acoustic treatment, the applicant developed a particular technique called “O-splice plate,” described in the documents FR-2,844,304 or U.S. Pat. No. 6,772,857. According to this technique, the acoustically resistive layer consists of a large number of strips arranged in the direction of flow of the streams and connected to one another by a large number of splice plates ensuring the uptake of forces and having a reduced width relative to the width of the strips in such a way as to ensure the continuity of the homogeneous nature of the open surface ratio.

InFIG. 1, an acoustic treatment panel was shown whose surface that is in contact with the stream of air is damaged and comprises a concave deformation16because of, for example, an accidental impact during flight (bird, ice, . . . ) or during maintenance (dropped tools, . . . ).

This concave deformation16tends to produce aerodynamic disturbances at the flow of the air stream that is in contact with said panel, to alter the acoustic treatment, and it can reduce the structural strength of the panel. Also, it is necessary to repair the panel to at least limit the aerodynamic disturbances.

According to a first operating procedure that is described inFIGS. 2A and 2B, a resin18is injected into the damaged cells or pipes of the alveolar structure in such a way as to fill the concave deformation, and then a front plate20that covers the resin18and that extends beyond the damaged zone is optionally arranged on the damaged zone in such a way as to be connected by gluing, riveting, etc., with the acoustically resistive layer10.

This front plate can be metal or composite material.

As illustrated inFIG. 3B, the front plate20is a flat surface and consequently has a zero open surface ratio although at the covered zone, the acoustic treatment is completely eliminated.

The object of another operating procedure described inFIGS. 3A to 3Dis to limit the impact of the repair on the acoustic treatment. According to this operating procedure, the alveolar structure12and the acoustically resistive layer10are removed at the concave deformation16in such a way as to obtain a recess22that is delimited by edges perpendicular to the reflective layer14, as illustrated inFIG. 3A.

A block24is cut out with shapes that are adapted to the recess22, whereby this block comprises an alveolar structure12′ that is covered by an acoustically resistive layer10′, with said shapes being identical to the alveolar structure12and the acoustically resistive layer10of the acoustic treatment panel to be repaired. This block24is introduced into the recess22, as illustrated inFIG. 3B.

To ensure the connection between the block24and the rest of the panel for the acoustic treatment, a splice plate26is used at the border separating the block24and the rest of the panel, arranged astride said border and connected to the block24and to the rest of the panel by gluing, riveting, etc., as illustrated inFIG. 3C. This splice plate26can come in the form of folds embedded in a resin.

Like the front plate20of the first operating procedure, the splice plate26has a zero open surface ratio although at the zone that is covered by said splice plate26, the acoustic treatment is completely eliminated. Contrary to the first operating procedure, the latter limits the impact of the repair on the acoustic treatment to the extent that the surface of the block24that is not covered by the splice plate26ensures an acoustic treatment.

Thus, the known repair operating procedures all lead to losses of surfaces treated on the acoustic level and produce discontinuities in the acoustic treatment.

This invention proposes an acoustic treatment panel with a junction zone that limits the discontinuities in the acoustic treatment.

For this purpose, the invention has as its object an acoustic treatment panel that comprises, on the one hand, at least two portions with edges that are spaced in at least one direction and with—from the outside to the inside—an acoustically resistive layer, at least one alveolar structure, and a reflective layer, and, on the other hand, a block that is inserted between the two edges that comprise—from the outside to the inside—an acoustically resistive layer that is arranged at said acoustically resistive layer of the two portions and at least one alveolar structure, characterized in that the block comprises at least one sector of alveolar structures with sloped pipes whose height h is less than the height H of the alveolar structure of the panel for the acoustic treatment, whereby said pipes are sloped in a direction such that the ends of the pipes are close to one of the edges of the portions at the acoustically resistive layer, and the opposite ends of said pipes are moved away from said edge and the reflective layer of the two portions in such a way as to house connecting means between said block and said panel.

According to another objective, the invention proposes a process for repair of an acoustic treatment panel whose purpose is to limit the impact of said repair on the acoustic treatment.

FIG. 4shows in a cutaway an acoustic treatment panel50whose so-called aerodynamic surface can be in contact with an air stream referenced by the arrow52.

This acoustic treatment panel comprises—from the outside to the inside—an acoustically resistive layer54of which one surface is in contact with the air stream52, at least one alveolar structure56, and a reflective layer58.

By way of example, an acoustic treatment panel can be arranged in a pipe of an aircraft nacelle.

According to the applications, the acoustic treatment panel can comprise several superposed alveolar structures56that are separated by an acoustically resistive layer.

Layer is defined as one or more layers that may or may not be of the same type.

According to one embodiment, the reflective layer58can be a non-perforated sheet or plate that is made of metal or composite material.

The alveolar structure56can comprise a large number of juxtaposed pipes that are blocked or partially blocked at each end. Each pipe is delimited by at least one wall that is essentially perpendicular to the reflective layer58and/or to the acoustically resistive layer54. Thus, the alveolar structure56comprises straight pipes.

According to one embodiment, the alveolar structure56comes in the form of a honeycomb that is made of metal or composite material.

However, the invention is not limited to these embodiments for the reflective layer and the alveolar structure.

According to the variants, the acoustically resistive layer54can comprise a layer or several layers that are mounted adjacent to one another.

According to one embodiment, the acoustically resistive layer54comes in the form of a plate with openings.

According to another variant, the acoustically resistive layer54comprises at least one porous layer and at least one reinforcement structure. In this case, the porous layer is a metal material, in particular a stainless steel mesh that is known to one skilled in the art. The reinforcement structure is a plate with openings. According to all of the variants, the acoustically resistive layer54comprises openings that make it possible to link the zones that are arranged on both sides of said acoustically resistive layer54.

According to an embodiment that is described in the documents FR-2,844,304 or U.S. Pat. No. 6,772,857, the acoustically resistive layer54consists of a large number of strips arranged in the direction of flow of the streams and connected to one another by a large number of splice plates ensuring the uptake of forces and having a reduced width relative to the width of the strips in such a way as to ensure the continuity of the homogeneous nature of the open surface ratio.

The repair process comprises a first stage that is described inFIG. 5, consisting in removing a portion of the alveolar structure56and the acoustically resistive layer56at the concave deformation60in such a way as to obtain a recess62that is delimited by at least one side wall64that is essentially perpendicular to the reflective layer58and/or the acoustically resistive layer54.

The second stage that is illustrated inFIG. 6consists in producing a block66that comprises—from the outside to the inside—an acoustically resistive structure68that defines a front surface and at least one alveolar structure70. The front face of the block66has a contour72whose shapes are adapted to those of the recess62when the acoustically resistive layer68of the block66is arranged at the acoustically resistive layer54of the panel50.

Thus, the side wall64and the contour72form a junction zone between two acoustic treatment panels, namely between the acoustic treatment panel50that is to be repaired and the one that is formed by the connected block66.

According to the invention, the alveolar structure70of the block66comprises sloped pipes74, whose height h is less than the height H of the alveolar structure56of the acoustic treatment panel.

The pipes74are sloped in such a way that, over at least a portion of the contour of the recess62, said pipes are contiguous with the side wall64of the recess62at the acoustically resistive layer54and moved away from the side wall64of the recess62close to the reflective layer58. This slope makes it possible to obtain a so-called junction space76between, on the one hand, the alveolar structure70of the block, and, on the other hand, the alveolar structure56and the reflective layer58of the acoustic treatment panel50.

The sloped pipes74provide the same acoustic response as the straight pipes while being lower in height, and the junction space76makes it possible to house connecting means78between the connected block66and the acoustic treatment panel50.

To limit the impact of repair on the acoustic treatment, the play between the contour72and the side wall64of the recess is to be the smallest possible. Preferably, the sloped pipes74are blocked at their ends opposite to the acoustically resistive layer68.

According to one embodiment, the block66can comprise a reflective layer that is flattened against the surface of the alveolar structure opposite to the one against which the acoustically resistive layer is applied.

According to another embodiment that is illustrated inFIGS. 6 and 7, the block66comprises a packing structure80that is made integral with the alveolar structure70whose outside shapes are adapted to those of the recess62and that blocks the pipes74at their ends that are opposite to the acoustically resistive layer68. Thus, the block66comprises a rear surface82that can be flattened against the reflective layer58and at least one side wall84that can be mounted adjacent to the side wall64of the recess62when the block66is installed.

Advantageously, the block66is attached to the reflective layer58using connecting means78such as gluing, riveting, etc., for example.

Advantageously, the pipes74of the alveolar structure70have cross-sections that are similar to those of the straight pipes of the alveolar structure of the panel50. However, the cross-sections could be different but impart the same response on the acoustic level.

Advantageously, the pipes form a non-zero angle to the normal to the acoustically resistive layer that varies on the order of 10 to 30°.

Preferably, the pipes form an angle α to the normal to the acoustically resistive layer on the order of 30°.

According to a first variant that is illustrated inFIG. 8, the block66can comprise several sectors86of alveolar structures, each sector having a suitable slope direction that is oriented in such a way that the ends of the pipes that are oriented in the direction of the reflective layer58are directed toward the center of the block.

In the case of a rectangular or square recess62, the block66comprises four sectors86that are delimited by the diagonals of the square or rectangle with a hollow pyramidal shape88in the central part under the acoustically resistive layer68. Even if it does not offer the same response on the acoustic level as the sloped pipes74, this hollow central shape88is active on the acoustic treatment level.

According to another variant that is illustrated inFIG. 9, the block66comprises two sectors of alveolar structures, with the two sectors having opposite slope directions, the ends of the sloped pipes74of the first sector being oriented in a first direction and the ends of the sloped pipes74of the second sector being oriented in a second direction that is opposite to the first.

In this case, the block66comprises a hollow central shape90that extends perpendicularly to the inclination plane with a triangular cross-section. According to this variant, the junction zones that are perpendicular to the inclination plane can be reinforced with splice plates92. Even in this case, the surface area that is covered by the splice plates92is smaller than the one that is covered by the necessary splice plates according to the repair processes of the prior art.

Preferably, the block66comprises at least two sectors, with the slope directions of the pipes of the two sectors being convergent in the direction of the reflective layer58.

By way of comparison, for a square repair zone of 200 mm on one side with a height H of 35 mm, if the first operating procedure of the prior art that is described byFIGS. 2A and 2Bis used, the surface of the front plate20that is not active on the acoustic level is on the order of 53,000 mm2.

If the second operating procedure of the prior art that is described byFIGS. 3A to 3Dis used, the non-active surface that is covered by the splice plates26on the acoustic level is on the order of 28,000 mm2.

If a block66with four sectors with pipes sloped at 30° is used, the surface that emerges from the concave central shape88(acoustically active but not homogeneous with the rest of the pipes) is on the order of 1,225 mm2.

The invention is not limited to the application described above.

Thus, the invention can be used to ensure the connection between two portions of the same acoustic panel or between two acoustic treatment panels. Thus, a block can be inserted between the straight edges of the two acoustic treatment panels, with the block comprising two edges, a first edge that is mounted adjacent to the edge of the first panel and a second edge that is mounted adjacent to the edge of the second panel. To limit the impact on the acoustic level of the junction between the two panels, the block comprises, on the one hand, at the first edge, a first sector of pipes that are sloped in a first direction in such a way that the ends of the pipes arranged at the acoustically resistive layer are close to the first edge and the opposite ends of said pipes are removed from the first edge, and, on the other hand, at the second edge, a second sector of pipes that are sloped in a second direction in such a way that the ends of the pipes arranged at the acoustically resistive layer are close to the second edge, and the opposite ends of said pipes are moved away from the second edge.

In all of the cases, the invention makes it possible to ensure acoustic continuity between at least two portions of alveolar structures with edges spaced in at least one direction, and it consists in using a block that comprises at least one sector of alveolar structures with pipes that are sloped in a direction in such a way that the ends of the pipes are close to one of the edges of the portions of alveolar structures at the acoustically resistive layer and the opposite ends of said pipes are moved away from said edge.