ASSEMBLY CONSTITUTING AN ACOUSTIC ABSORBENT MATERIAL

Abstract

ASSEMBLY CONSTITUTING AN ACOUSTIC ABSORBENT MATERIAL The invention relates to an assembly (100) constituting an acoustically absorbing material and comprising a first plate (102) perforated with holes (106), a second plate (104), between the first plate (102) and the second plate (104), a honeycomb structure (112) which has four cages (120), and for each cage (120), an intermediate plate (110) is fixed in said cage (120) between the first plate (102) and the second plate (104), wherein each intermediate plate (110) is traversed by at least one through hole (132) and wherein the distance between the first plate (102) and the intermediate plate (110) is different for each cage (120) of the honeycomb structure (112). Such an assembly makes it possible to obtain broadband attenuation. Fig. 1

Description

Title of the invention: ASSEMBLY CONSTITUTING AN ACOUSTIC ABSORBENT MATERIAL Technical field

[0001] The present invention relates to an assembly constituting an acoustically absorbing material. PREVIOUS STATE OF THE ART

[0002] During its operation, an aircraft engine generates noise. This engine is housed in a nacelle, and to reduce this noise, it is known to install assemblies constituting an acoustically absorbing material around the engine in the nacelle structure.

[0003] Such assemblies constituting an acoustically absorbing material take, for example, the form of honeycomb structures. Such a honeycomb structure comprises two parallel plates, one of which is perforated, and between which hexagonal cells are arranged juxtaposed to one another.

[0004] Although such assemblies give good results from an acoustic point of view, it is desirable to find an assembly constituting an acoustically absorbing material that allows for the attenuation of several acoustic frequencies. Description of the invention

[0005] An object of the present invention is to propose an assembly constituting an acoustically absorbing material which can attenuate several acoustic frequencies and which has a broadened attenuation peak.

[0006] To this end, an assembly is proposed that constitutes an acoustically absorbent material and comprises:

[0007] - a first plate pierced with holes,

[0008] - a second plate,

[0009] - between the first plate and the second plate, a honeycomb structure which includes at least two cages, and

[0010] - for each cage, an intermediate plate is fixed in said cage between the first plate and second plate, where each intermediate plate is traversed by at least one through hole and where the distance between the first plate and the intermediate plate is different for each cage of the honeycomb structure.

[0011] Such an assembly makes it possible to obtain attenuation over a wider band.

[0012] According to a particular embodiment, the assembly comprises, for each intermediate plate, a tube opening at both ends, one end of each tube being fixed to the intermediate plate at the level of the through hole associated with the intermediate plate, each tube is placed between the first plate and the intermediate plate and the tubes all have the same dimensions.

[0013] According to a particular embodiment, the assembly comprises, for each intermediate plate, a tube opening at both ends, one end of each tube is fixed to the intermediate plate at the level of the through hole associated with the intermediate plate, each tube is arranged between the first plate and the intermediate plate and the tubes have different dimensions.

[0014] According to a particular embodiment, the assembly comprises, for one of the two intermediate plates, a tube opening at both ends, one end of said tube being fixed to the intermediate plate at the level of the through hole associated with the intermediate plate, said tube being disposed between the first plate and the intermediate plate. In particular, the other of the two intermediate plates is without a tube.

[0015] The invention also proposes an assembly comprising at least two sets as described above, where the two sets are joined together, and where the distance between the first plate and the intermediate plate is different for each cage of the honeycomb structure of each set. Brief description of the drawings

[0016] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which:

[0017] [Fig. 1] is a cross-sectional view of an assembly constituting an acoustically absorbing material according to a first embodiment of the invention,

[0018] [Fig.2] is a cross-sectional view of an assembly according to a second embodiment of the invention, and

[0019] [Fig.3] is a cross-sectional view of an assembly according to a third embodiment of the invention.

[0020] DETAILED STATEMENT OF IMPROVEMENTS

[0021] Fig. 1 shows an assembly 100 constituting an acoustically absorbing material according to a first embodiment of the invention, and Figs. 2 and 3 show, respectively, an assembly 100 according to a second and a third embodiment of the invention. The assembly 100 comprises a first plate 102 and a second plate 104, which are spaced apart. One of the plates, here the first plate 102, is perforated with holes 106 that pass through it to allow the passage of acoustic waves. The other plate 104 is solid.

[0022] The assembly 100 also includes, between the first plate 102 and the second plate 104, a honeycomb structure 112 comprising at least two cages 120, each hollow and delimited by walls 124 extending between the first plate 102 and the second plate 104. When the assembly 100 comprises four cages 120, it can be considered an assembly comprising two assemblies 100, each comprising at least two cages 120. Each cage 120 delimits a hexagonal cell, but other shapes are possible. The cages 120 are here placed side by side in a line, and each pair of adjacent cages 120 shares a common wall 124. Of course, it is also possible for the four cages 120 to be arranged in a square. Of course, a set of 100 can include more than two cages of 120, and an assembly can include more than two sets of 100.

[0023] The advantage of having more than two 120 cages is to be able to attenuate several different frequencies and thus broaden the attenuation spectrum.

[0024] For each cage 120, an intermediate plate 110 is arranged between the first plate 102 and the second plate 104. The three plates 102, 104, and 110 are parallel. Thus, for each cage 120, an intermediate plate 110 is fixed to said cage 120 by gluing, welding, etc. For each cage 120 of the assembly 100, the vertical position of the intermediate plate 110 differs from the vertical position of the intermediate plates 110 of the other cages 120 of the assembly 100. In other words, the distance between the first plate 102 (respectively the second plate 104) and the intermediate plate 110 is different for each cage 120 of the honeycomb structure 112.

[0025] Each cage 120 is thus divided by the intermediate plate into a first volume 120a between the first plate 102 and the intermediate plate 110 and into a second volume 120b between the second plate 104 and the intermediate plate 110.

[0026] Each intermediate plate 110 is traversed by at least one hole through 132 and there is thus a fluidic continuity between each first volume 120a and the associated second volume 120b.

[0027] Each first volume 120a acts as a quarter wave resonator which attenuates high acoustic frequencies and the placement of four first volumes 120a of different dimensions makes it possible to attenuate several frequencies.

[0028] It is then possible to combine several sets 100 with different characteristics to attenuate different frequencies depending on where the sets 100 are placed.

[0029] In the embodiment of the invention shown in [Fig. 1] and [Fig. 2], the assembly 100 also includes, for each intermediate plate 110, a tube 130 opening at both ends and extending perpendicularly to the intermediate plate 110.

[0030] In the embodiment of the invention shown in [Fig.3], there are only two tubes 130 and these tubes 130 have the same arrangement as those of the other embodiments.

[0031] One end of each tube 130 is fixed to the intermediate plate 110 at the through hole 132 associated with the intermediate plate 110 and each tube 130 is disposed in the first volume 120a and opens into it by its other end, that is to say that each tube 130 is disposed between the first plate 102 and the intermediate plate 110. The fixing of the tubes 130 to the intermediate plate 110 is carried out for example by welding, gluing, etc.

[0032] The second volume 120b and the associated tube 130 form a Helmholtz resonator which attenuates low acoustic frequencies.

[0033] In the embodiment of the invention presented in [Fig.1], the four tubes 130 all have the same dimensions, that is to say the same length in the first volume 120a, the same outside diameter and the same inside diameter.

[0034] According to a particular embodiment, the distance between the first plate 102 and the intermediate plate 110 is for a first cage 120 between 3 mm and 7 mm, for example equal to 5 mm, for a second cage 120 between 10 mm and 14 mm, for example equal to 12 mm, for a third cage 120 between 16 mm and 20 mm, for example equal to 18 mm, and for a fourth cage 120 between 26 mm and 30 mm, for example equal to 28 mm. At the same time, the distance between the second plate 104 and the intermediate plate 110 is for the first cage 120 between 31 mm and 35 mm, for example equal to 33 mm, for the second cage 120 between 24 mm and 28 mm, for example equal to 26 mm, for the third cage 120 between 18 mm and 22 mm, for example equal to 20 mm, and for the fourth cage 120 between 8 mm and 12 mm, for example equal to 10 mm.

[0035] In the embodiment of the invention shown in [Fig.2], at least two tubes 130 have different dimensions, in particular different lengths and internal diameters.

[0036] In the embodiment of the invention shown in [Fig. 3], the two tubes 130 have the same dimensions, that is, the same length in the first volume 120a, the same outer diameter, and the same inner diameter. In the same embodiment, the two other cages 120 do not have tubes, and the intermediate plates 110 are only pierced with through holes 132, of which there are four per intermediate plate 110.

Claims

Demands

1. Assembly (100) constituting an acoustically absorbing material and comprising: - a first plate (102) pierced with holes (106), - a second plate (104), - between the first plate (102) and the second plate (104), a honeycomb structure (112) which has at least two cages (120), and - for each cage (120), an intermediate plate (110) is fixed in said cage (120) between the first plate (102) and the second plate (104), wherein each intermediate plate (110) is traversed by at least one through hole (132) and wherein the distance between the first plate (102) and the intermediate plate (110) is different for each cage (120) of the honeycomb structure (112).

2. Assembly (100) according to claim 1, characterized in that said assembly comprises for each intermediate plate (110), a tube (130) opening at both ends, in that one end of each tube (130) is fixed to the intermediate plate (110) at the level of the through hole (132) associated with the intermediate plate (110), in that each tube (130) is arranged between the first plate (102) and the intermediate plate (110) and in that the tubes (130) all have the same dimensions.

3. Assembly (100) according to claim 1, characterized in that said assembly comprises for each intermediate plate (110), a tube (130) opening at both ends, in that one end of each tube (130) is fixed to the intermediate plate (110) at the level of the through hole (132) associated with the intermediate plate (110), in that each tube (130) is disposed between the first plate (102) and the intermediate plate (110) and in that the tubes (130) have different dimensions.

4. Assembly (100) according to claim 1, characterized in that said assembly comprises for one of the two intermediate plates (110), a tube (130) opening at both ends, in that one of the ends of said tube (130) is fixed to the intermediate plate (110) at the level of the through hole (132) associated with the intermediate plate (110), in that said tube (130) is disposed between the first plate (102) and the intermediate plate (110).

5. Assembly comprising at least two sets (100) according to any one of claims 1 to 4, wherein the two sets (100) are joined together, and wherein the distance between the first plate (102) and the intermediate plate (110) is different for each cage (120) of the honeycomb structure (112) of each set (100).

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