ACOUSTIC PANEL FOR TURBINE ENGINE

Description

Technical field

[0001] The present disclosure relates to an acoustic panel for a turbomachine. It also relates to a turbomachine nacelle comprising such an acoustic panel. Prior art

[0002] As represented in figure 1 , a turbomachine 10 conventionally comprises a nacelle 11 in which an engine or a turbojet is housed. The nacelle of a turbomachine is commonly equipped with an acoustic panel 12 to limit the noise level emitted by the engine or the turbojet.

[0003] Such an acoustic panel 12 absorbs noise according to the Helmholtz resonator principle. For this purpose, the acoustic panel generally comprises a perforated front acoustic wall to allow the passage of sound waves, a rear wall and a cellular structure, comprising a plurality of cells, which is interposed between the front wall and the rear wall.

[0004] Each cell extends between the rear wall and the front acoustic wall along a principal direction of sound wave propagation. The dimension of the cells between the front acoustic wall and the rear wall, in the principal direction, makes it possible to determine the frequency of the sound waves for which the acoustic attenuation is maximum. Typically, the acoustic attenuation is maximum for sound waves whose wavelength is equal to or close to four times the dimension of the cell in the principal direction (the length being inversely proportional to the frequency of the sound waves). In contrast, the acoustic attenuation is zero for sound waves whose wavelength is equal to or close to the dimension of the cell in the principal direction.

[0005] Current turbomachinery is tending towards a larger diameter geometry, with rotating elements, such as the fan, which are slower and therefore produce noise with a lower frequency. Thus, there is a need to increase the dimension of the cells, in the main direction, so that they allow acoustic attenuation of noise with a lower frequency.

[0006] However, the nacelle of turbomachines tends to become shorter and thinner in order to limit drag. The acoustic panels equipping the nacelle must therefore have a reduced thickness, which limits the sizing of the cells to effectively attenuate low frequencies.

[0007] To solve this drawback, it is known to arrange obstacles 19 extending inside each cell 18 transversely to the main direction X as shown in figure 2. The sound waves then propagate in the cell following an “S” trajectory which lengthens the distance traveled by the sound waves in the cell 18. Thus, for a given cell dimension in the main direction X, such a cell 18 allows acoustic attenuation of sound waves having a lower frequency. The thickness of an acoustic panel 12 comprising such cells 18 can thus be reduced while allowing attenuation of low frequency noise.

[0008] An acoustic panel 12 comprising such cells 18 is generally produced by a stack of pre-cut, folded, interconnected plates which have been expanded under the effect of a compressive load applied to the stack. Such acoustic panels 12 are unsatisfactory in that their manufacture is complex and in that the obstacles inside the cells do not have a uniform geometry. Document WO2019 / 043344 discloses an acoustic panel according to the prior art. Summary

[0009] This disclosure improves the situation.

[0010] An acoustic panel for a turbomachine is proposed, the acoustic panel comprising at least: a first corrugated strip and a second corrugated strip each comprising an alternation, in a first direction, of first ridges and second ridges connected by flanks, said first strip and said second strip being attached to each other in a second direction transverse to the first direction, so as to form a plurality of cells which are each delimited, in the second direction, by a first ridge of the first strip and a first ridge of the second strip, each cell extending in a third direction transverse to the first direction and to the second direction, a third strip inserted, in the second direction, between the first strip and the second strip, the third strip comprising a first side wall resting, in the second direction, on the first strip,the third strip further comprising at least one tab which extends inside one of the cells, at least partly transversely to the third direction of the associated cell, said at least one tab being connected, at a first end edge in the second direction, to the first side wall, said at least one tab delimiting all or part of a passage in the third direction inside the associated cell.

[0011] THEsound waves propagate inside the cell in the third direction. In other words, the third direction is a direction of propagation of sound waves inside the cell. The first tab thus forms an obstacle to the propagation of sound waves in the cell, the latter being forced to propagate through the passage delimited by the first tab. The distance traveled by the sound waves inside the associated cell is then increased. Thus, the dimension of the acoustic panel is reduced in the third dimension while maintaining acoustic attenuation of low frequencies. In addition, such a panel can be manufactured from preformed strips and does not require the application of constraints on the strips to form each obstacle inside a cell. Such an acoustic panel therefore has the advantage of being easy and quick to manufacture.

[0012] The first side wall may be attached to the first strip and / or the second strip, in particular by an adhesive. The at least one tab may be connected to the first side wall by a fold line. Also, the correct positioning and attachment of the third strip relative to the first strip and the second strip is simple to implement and allows for identical geometry of the obstacles for all the cells of the acoustic panel. The at least one tab may extend perpendicular to the first side wall. The first strip and the second strip may form the plurality of cells in the first direction. The third strip may have a dimension, in the first direction, which is similar to the dimensions of the first strip and the second strip in the first direction.

[0013] The first direction and the second direction may be coplanar. The second direction may be perpendicular to the first direction. The third direction may be perpendicular to the first direction and / or the second direction. The second direction may be a direction normal to the crests of the first sheet and the second sheet.

[0014] The passage may be delimited by a free edge of the tongue and one of the first ridge of the first strip and the first ridge of the second strip delimiting the associated cell.

[0015] The passage may be delimited, in the second direction, by a free edge of the tongue and one of the first ridge of the first strip and the first ridge of the second strip delimiting the associated cell.

[0016] Each cell may have a cross-section in the associated third direction which is hexagonal, and in which said at least one tab comprises a central part which extends, in the second direction, between the first ridges of the first strip of the second strip which delimit the associated cell, and two lateral parts which each extend, in the second direction, between flanks of the first strip and of the second strip facing each other in the second direction which delimit the associated cell.

[0017] Thus, when each cell has a cross-section to the associated third direction which is hexagonal, it is ensured that the tab extends over the entire cross-section of the associated cell, with the exception of the passage delimited by the tab.

[0018] The central portion of the tab may extend transversely to the third direction of the associated cell. The lateral portions of the tab may each extend obliquely to the third direction of the associated cell.

[0019] Each side part can be connected to the central part by a fold line.

[0020] The passage may be a closed-contour opening formed in the tab. A second end edge of the tab, in the second direction, may be joined with the first ridge of the second strip delimiting the associated cell.

[0021] Therefirst side wall of the third strip may comprise an alternation, in the first direction, of first ridges and second ridges connected by flanks, each first ridge and second ridge of the first side wall being respectively supported in the second direction on one of the first ridges and one of the second ridges of the first strip. In other words, the first side wall may be attached in a complementary manner to the first strip.

[0022] Each first ridge and second ridge of the first side wall may be connected to one of the adjacent flanks by a fold line.

[0023] The third strip may further comprise a second side wall bearing, in the second direction, on the second strip, said at least one tab being connected, at a second end edge in the second direction, to the second side wall.

[0024] The second side wall can be fixed to the second strip, in particular by an adhesive.

[0025] The second side wall of the third strip may comprise an alternation, in the first direction, of first ridges and second ridges connected by flanks. Each first ridge and second ridge of the second side wall may respectively bear in the second direction on one of the first ridges and one of the second ridges of the second strip. The second side wall may be attached in a complementary manner to the second strip.

[0026] Each first ridge and second ridge of the second side wall may be connected to one of the adjacent flanks by a fold line.

[0027] Each second ridge of the first sidewall of the third strip, and optionally each second ridge of the second sidewall of the third strip, may be clamped in the second direction between one of the second ridges of the first strip and one of the second ridges of the second strip.

[0028] The third strip may comprise a plurality of tabs offset from each other in the third direction of the associated cell, and in which the passages delimited in whole or in part by a first tab and a second consecutive tab in the third direction are offset from each other in a direction transverse to the third direction of the associated cell.

[0029] The third strip comprises a first tab and a second tab which are offset from each other in the third direction of the associated cell, the passage delimited in whole or in part by the first tab and the passage delimited in whole or in part by the second tab being offset from each other in a direction transverse to the third direction of the associated cell. The propagation path of the sound waves in the cell thus forms a chicane or an "S" so as to increase the distance traveled by the sound waves in the cell.

[0030] The second sidewall may include a first portion connected to the first tab and a second portion connected to the second tab, the first portion and the second portion of the second sidewall being discontinuous.

[0031] The third strip may comprise at least one tab associated with each cell formed by the first strip and the second strip.

[0032] The acoustic panel may further comprise at least one acoustically permeable septum that extends within one of the cells, transversely to the third direction of the associated cell. The septum may extend within the passage delimited in whole or in part by said at least one tab. The septum makes it possible to divide the associated cell into two stages in the third direction. The septum may be a multi-perforated membrane to allow acoustic communication between the stages. Such a septum allows acoustic absorption over a wider frequency range. Such an acoustic panel is generally referred to as a double-degree-of-freedom (DDOF) acoustic panel, as opposed to a single-degree-of-freedom (SDOF) acoustic panel.

[0033] The first strip, the second strip and / or the third strip may be made of a metallic material, such as aluminum, or of a thermosetting material.

[0034] The first strip and / or the second strip can be obtained by stamping. The third strip can be obtained by bending.

[0035] According to another aspect, a turbomachine nacelle is described comprising at least one acoustic panel as described above.

[0036] According to another aspect, there is described a method of manufacturing an acoustic panel as described above, the method comprising the steps: i providing the first corrugated strip and the second corrugated strip each comprising a plurality of first ridges and second ridges connected by flanks, ii providing the third strip, iii positioning the first side wall of the third strip resting on the first strip in the second direction, iv bringing the second strip to the first strip to form the plurality of cells, with the third strip interposed, in the second direction, between the first strip and the second strip, said at least one tab extending inside one of the cells.

[0037] Step i may include the following subsidiary steps: a1 providing a first strip and a second strip each having a flat shape, b1 forming the first strip and the second strip so that they each have a corrugated shape with alternating first ridges and second ridges connected by flanks.

[0038] Step b1 can be carried out by stamping. The corrugated shape of the first strip and the second strip can be obtained by passing the first strip and the second strip between two notched rollers.

[0039] Step i may further comprise a step c1 consisting of heating the first strip and the second strip, in particular when these are made of a thermosetting material. The first strip and the second strip may each be heated to a stabilization state in which they are rigid.

[0040] The manufacturing method may further comprise a step v consisting of heating the acoustic panel, in particular when the first strip, the second strip and the third strip are made of a thermosetting material. Heating the strips allows polymerization allowing the strips to be fixed together. Step v may be carried out with the strips arranged on a tool having a curve so as to give the strips a curve.

[0041] THE The method may comprise a step ii' of depositing a layer of adhesive on each side of the third strip in the second direction. Step ii' may be carried out between step ii and step iii.

[0042] Alternatively, step v may consist of crosslinking each layer of adhesive, in particular by heating the acoustic panel.

[0043] Step ii may include the subsidiary steps: a2 providing a third strip having a planar shape, b2 forming the fold lines delimiting each first ridge and second ridge of the first side wall and the second side wall of the third strip, c2 forming at least one pair of fold lines on the third strip, each fold line of said pair delimiting one of the end edges in the second direction of said at least one tab, the fold lines of said pair being joined at each first ridge of the first side wall and the second side wall, d2 making a cut in the third strip forming the passage delimited in whole or in part by said at least one tab, e2 folding the first side wall and the second side wall so that they each have a corrugated shape with alternating first ridges and second ridges connected by flanks,f2 folding said at least one tab relative to the first side wall, g2 folding the second side wall relative to said at least one tab and to the first side part so that each second ridge of the second side wall is opposite one of the second ridges of the first side wall.

[0044] Where appropriate, step c2 may further consist of forming the fold line between the central part of said at least one tab and each lateral part.

[0045] Step d2 can be performed by laser.

[0046] Steps e2, g2 and f2 may be carried out by a folder, in particular a manual or automatic folder. Said at least one tab may in particular be folded at 90° relative to the first side wall during step f2.

[0047] Step ii may further comprise a step h2 consisting of heating the third strip, in particular when the latter is made of a thermosetting material. The third strip may be heated to a stabilization state in which it is rigid. Brief description of the drawings

[0048] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: Figure 1 is a partial schematic in axial section of a turbomachine of the prior art; Figure 2 is a partial perspective schematic of a prior art acoustic panel cell; Figure 3 is a partial schematic view of an acoustic panel according to the description; Figure 4 is a partial schematic sectional view of the acoustic panel of the figure 3 ; Figure 5is a schematic perspective view of the third strip of the acoustic panel of the figure 3 ; Figure 6 is a functional diagram of the manufacturing process of the acoustic panel of the figure 3 ; Figure 7 is a functional diagram of a sub-process implemented during a step of the process of the figure 8 ; Figure 8 is a schematic perspective view of the third strip of the acoustic panel of the Figure 5 before folding; Figure 9 includes the Figures 9A and 9B illustrating different configurations of the third strip of the acoustic panel of the Figure 5 being folded. Description of the embodiments

[0049] Reference is now made to the figures 3 And 4which represent an acoustic panel 12 for a turbomachine. The acoustic panel 12 can in particular equip a turbomachine nacelle. The acoustic panel 12 here comprises an acoustic front wall 14 and a rear wall 16, each being visible at the figure 4 . The acoustic front wall 14 and the rear wall 16 are parallel to each other. The front wall and the rear wall are spaced apart and opposite each other in a main direction of the acoustic panel. The main direction of the acoustic panel is taken in the direction of the thickness of the acoustic panel. The front acoustic wall 14 is multi-perforated so as to be acoustically permeable.

[0050] The acoustic panel comprises a first sheet 20 and a second sheet 22 arranged between the front wall 14 and the rear wall 16. The first sheet 20 and the second sheet 22 here each extend in the main direction of the acoustic panel 12. The first sheet 20 and the second sheet 22 are each corrugated. The first sheet 20 and the second sheet 22 each comprise an alternation, in a first direction A1, of first ridges 20a, 22a and second ridges 20b, 22b connected by flanks 20f, 22f. The first direction A1 may be transverse to the main direction of the acoustic panel. The first direction A1 is here perpendicular to the main direction of the acoustic panel.

[0051] The first strip 20 and the second strip 22 are connected to each other in a second direction A2 transverse to the first direction A1, so as to form a plurality of cells 18. The first strip 20 and the second strip 22 form the plurality of cells 18 in the first direction A1. In other words, the first strip 20 and the second strip 22 form a row of cells 18 in the first direction A1. The first direction A1 and the second direction A2 are coplanar. The second direction A2 is here perpendicular to the first direction A1. The second direction A2 is a direction normal to each peak 20a, 20b, 22a, 22b of the first strip 20 and the second strip 22.

[0052] Each cell 18 is delimited in the main direction of the acoustic panel 12 by the rear wall 16 and the front wall 14. Each cell 18 is delimited, in the second direction A2, by a first crest 20a of the first sheet 20 and a first crest 22a of the second sheet 22. Each cell 18 extends in a third associated direction A3 which is transverse to the first direction A1 and to the second direction A2. The sound waves propagate inside each cell in the third associated direction A3. In other words, the third direction A3 of each cell 18 is a direction of propagation of the sound waves inside the cell 18. The third direction A3 is here perpendicular to the first direction A1 and to the second direction A2. Also, the third direction A3 associated with each cell 18 coincides with the main direction of the acoustic panel 12.Each cell 18 has a cross-section to the associated third direction A3 which is hexagonal.

[0053] The acoustic panel 12 further comprises a third strip 30 more particularly visible at figures 5 , 8 And 9 The third strip 30 is interposed, in the second direction A2, between the first strip 20 and the second strip 22. The third strip 30 may have a dimension, in the first direction A1, which is similar to the dimensions of the first strip 20 and the second strip 22 in the first direction A1.

[0054] The third strip 30 comprises a first side wall 32 resting, in the second direction A2, on the first strip 20. The first side wall 32 of the third strip 30 comprises an alternation, in the first direction, of first ridges 32a and second ridges 32b connected by flanks 32f. Each first ridge 32a and second ridge 32b of the first side wall 32 bears respectively in the second direction A2 on one of the first ridges 20a and one of the second ridges 20b of the first strip 20. In other words, the first side wall 32 cooperates by complementary shape with the first strip 20. Each first ridge 32a and second ridge 32b of the first side wall 32 is here connected to one of the adjacent flanks 32f by a fold line J. The first side wall 32 of the third strip 30 is fixed to the first strip 20, for example by means of an adhesive.

[0055] The third strip 30 further comprises a first tab 34 and a second tab 34. The first tab 34 and the second tab 34 extend inside one of the cells 18, at least partly transversely to the third direction A3 of the associated cell 18. Each tab 34 is connected, at a first end edge in the second direction A2, to the first side wall 32. Each tab 34 is here connected to the first side wall 32 by a fold line K1. Each tab 34 may extend perpendicular to the first side wall 32.

[0056] The first tab 34 and the second tab 34 are offset from each other in the third direction A3 of the associated cell. For this purpose, the first tab 34 is connected to a first end of the first side wall 32 in the third direction A3. The second tab 34 is connected to a second end of the first side wall 32 in the third direction A3. The third strip 30 may comprise a plurality of first tabs 34 and a plurality of second tabs 34, a first tab 34 and a second tab 34 being associated with each cell formed by the first strip 20 and the second strip 22.

[0057] Each tab 34 delimits all or part of a passage 36 in the third direction A3 inside the associated cell 18. The first tab 34 forms an obstacle to the propagation of sound waves in the cell 18. The sound waves are forced to propagate through the passage 36 delimited in whole or in part by the first tab 34. The distance traveled by the sound waves inside the associated cell 18 is then increased. Thus, attenuates sound waves having a lower frequency while maintaining a thin acoustic panel 12.

[0058] In particular, the passage 36 delimited, in whole or in part, by the first tab 34 and the passage 36 delimited, in whole or in part, by the second tab 34 are offset relative to each other in the second direction A2 to the third direction A3 of the associated cell 18. The propagation trajectory of the sound waves in the cell thus forms a chicane or an “S” so as to further increase the distance traveled by the sound waves in the cell 18.

[0059] Each passage 36 is here delimited, in the second direction A2, by a free edge of the associated tongue 34 and one of the first ridge 20a of the first strip 20 and the first ridge 22a of the second strip 22 delimiting the associated cell 18. In particular, the passage 36 delimited by the first tongue 34 is here delimited, in the second direction A2, by a free edge of the first tongue 34 and the first ridge 22a of the second strip 22. Similarly, the passage 36 delimited by the second tongue 34 is here delimited, in the second direction A2, by a free edge of the second tongue 34 and the first ridge 20a of the first strip 20.

[0060] Each tab 34 comprises a central portion 34a which extends, in the second direction A2, between the first ridges 20a, 22a of the first strip 20 and of the second strip 22 which delimit the associated cell 18. The central portion 34a of the tab 34 extends transversely to the third direction A3 of the associated cell 18. Each tab 34 also comprises two lateral portions 34b on each side of the central portion 34a in the first direction A1. Each lateral portion 34b extends, in the second direction A2, between flanks 20f, 22f of the first strip 20 and of the second strip 22 facing each other in the second direction A2 and which delimit the associated cell 18. The lateral parts 34b of the tab 34 each extend obliquely relative to the third direction A3 of the associated cell 18. Each lateral part 34b is here connected to the central part 34a by a fold line L.Thus, when each cell 18 has a cross-section to the associated third direction A3 which is hexagonal, it is ensured that the tongue 34 extends over the entire cross-section of the associated cell 18 to form an obstacle to the propagation of sound waves, with the exception of the passage 36 delimited by the tongue 34.

[0061] The third strip 30 further comprises a second side wall 38 bearing, in the second direction A2, on the second strip 22. The second side wall 38 of the third strip 30 comprises an alternation, in the first direction A1, of first ridges 38a and second ridges 38b connected by flanks 38f. Each first ridge 38a and second ridge 38b of the second side wall 38 bears respectively, in the second direction A2, on one of the first ridges 22a and one of the second ridges 22b of the second strip 22. In other words, the second side wall 38 cooperates by complementary shape with the second strip 22. Each first ridge 38a and second ridge 38b of the second side wall 38 is here connected to one of the adjacent flanks by a fold line M. The second side wall 38 of the third strip 38 is fixed to the second strip 22, for example by means of an adhesive.

[0062] Eachsecond ridge 38b of the second side wall 38 bears, in the second direction A2, against one of the second ridges 32b of the first side wall 32. Each second ridge 32b of the first side wall 32 of the third strip 30, and each second ridge 38b of the second side wall 38 of the third strip 30 is clamped, in the second direction A2, between one of the second ridges 20b of the first strip 20 and one of the second ridges 22b of the second strip 22.

[0063] Each of the first tab 34 and second tab 34 is connected, at a second end edge, in the second direction A2, to the second side wall 38. The first tab 34 is connected to a first end of the second side wall 38 in the third direction A3. The second tab 34 is connected to a second end of the second side wall 38 in the third direction A3. Each of the first tab 34 and second tab 34 is here connected to the second side wall 38 by a fold line K2. The second side wall 38 here comprises a first portion connected to the first tab 34 and a second portion connected to the second tab 34, the first portion and the second portion of the second side wall 38 being discontinuous.

[0064] The acoustic panel may further comprise at least one acoustically permeable septum which extends inside the cell 18, transversely to the associated third direction A3. A septum may in particular extend inside the passage 36 delimited in whole or in part by each tab 34.

[0065] The first strip 20, the second strip 22 and / or the third strip 30 may be made of a metallic material, such as aluminum. Alternatively, the first strip 20, the second strip 22 and / or the third strip 30 may be made of a thermosetting material. According to a particular example, the first strip 20 and the second strip 22 are made of a metallic material and the third strip 30 is made of a thermosetting material. According to another particular example, the first strip 20, the second strip 22 and the third strip 30 are all made of a thermosetting material.

[0066] As will be seen in more detail below, the first strip 20, the second strip 22 and the third strip 30 are preformed before being assembled to form the acoustic panel. The first strip 20 and the second strip 22 can be obtained by stamping. The third strip 30 can be obtained by bending. Such a panel can thus be manufactured from preformed strips and does not require the application of compressive loads on the strips to form each obstacle inside a cell. Such an acoustic panel 12 therefore has the advantage of being easy and quick to manufacture. Also, the correct positioning of each obstacle inside one of the cells is simpler to implement.

[0067] There figure 6 represents a functional diagram of a method 100 for manufacturing the acoustic panel 12 as described above.

[0068] The method 100 comprises a first step 110 of providing the first corrugated strip 20 and the second corrugated strip 22 each comprising a plurality of first ridges 20a, 22a and second ridges 20b, 22b connected by flanks. The first step 110 may comprise a first subsidiary sub-step of providing a first strip 20 and a second strip 22 each having a planar shape. The first step may comprise a second subsidiary sub-step of forming the first strip 20 and the second strip 22 so that they each have a corrugated shape with alternating first ridges 20a, 22a and second ridges 20b, 22b connected by flanks 20f, 22f. The second subsidiary sub-step may be carried out by stamping.In other words, the corrugated shape of the first strip 20 and the second strip 22 can be obtained by passing the first strip 20 and the second strip 22 between two notched rollers. The first step 110 can comprise a third subsidiary sub-step consisting of heating the first strip 20 and the second strip 22, in particular when these are made of a thermosetting material. The first strip 20 and the second strip 22 can, in particular, each be heated to a stabilization state in which they are rigid.

[0069] The method 100 comprises a second step 120 consisting of providing the third strip 30. The figure 7 represents a functional diagram of a sub-process 200 implemented during the second step 120.

[0070] The sub-process 200 comprises a first step 210 consisting of providing a third strip 30 having a planar shape.

[0071] The sub-process comprises a second step 220 consisting of forming the folding lines J, M delimiting each first peak 32a, 38a and second peak 32b, 32b of the first side wall 32 and of the second side wall 38 of the third strip 30.

[0072] THE sub-process comprises a third step 230 consisting of forming a pair K of fold lines K1, K2 on the third strip 30, each pair K of fold lines K1, K2 being associated with a series of tabs 34 intended to extend each into one of the cells formed by the first strip 20 and the second strip 22. In the example shown, two pairs K of fold lines K1, K2 are formed, one of the pairs K being associated with a series of first tabs 34 and the other pair K being associated with a series of second tabs 34.

[0073] Each fold line K1, K2 of one of the pairs K delimits, in the second direction A2, one of the end edges of each tab 34 of the associated series of tabs 34. The fold lines K1, K2 of each pair K being joined at each first ridge 32a, 38a of the first side wall 32 and of the second side wall 38.

[0074] When the third strip 30 has a plane shape as visible in the figure 8, the first side wall 32 is arranged between the two pairs K of fold lines K1, K2. Also, the first portion of the second side wall 38 is arranged on one side of the pair of fold lines K1, K2 associated with the series of first tabs 34, which is opposite the first side wall 32. Similarly, the second portion of the second side wall 38 is arranged on one side of the pair of fold lines associated with the series of second tabs 34, which is opposite the first side wall 32. Remarkably, the first portion and the second portion of the second side wall 38 are arranged at opposite end edges of the third strip 30 in a planar configuration.

[0075] In the third sub-step 230 of the sub-process 200, the fold line L between each lateral portion 34b and the central portion 34a of each tab 34 is also formed.

[0076] The sub-process 200 comprises a fourth step 240 consisting of making a plurality of cuts in the third strip 30, each cut forming the passage 36 delimited in part by each tab 34. The fourth step 240 of the sub-process 200 can be carried out by laser for example.

[0077] The sub-process 200 comprises a fifth step 250 consisting of folding the first side wall 32 and the second side wall 38 so that they each have a wavy shape with alternating first ridges 32a, 38a and second ridges 32b, 38b connected by flanks 32f, 38f.

[0078] The sub-process 200 comprises a sixth step 260, shown in Figure 9A , consisting of folding each tab 34 relative to the first side wall 32. Each tab 34 can in particular be folded at 90° relative to the first side wall 32.

[0079] The sub-process 200 comprises a seventh step 270, shown in Figure 9B , consisting of folding the first portion of the second side wall 38 relative to each first tab 34 and the second portion of the second side wall 38 relative to each second tab 34 so that each second ridge 38b of the second side wall 38 is brought opposite one of the second ridges 32b of the first side wall 32.

[0080] The sixth step 260 and the seventh step 270 can be performed simultaneously.

[0081] The fifth step 250, the sixth step 260 and the seventh step 280 of the sub-process 200 can be carried out by a folder, in particular a manual or automatic type folder.

[0082] THEsub-process 200 comprises an eighth step 280 consisting of heating the third strip 30, in particular when the latter is made of a thermosetting material. The third strip 30 can be heated to a stabilization state in which it is rigid.

[0083] The method 100 comprises a third step 130 consisting of positioning the first side wall 32 of the third strip 30 resting on the first strip 20 in the second direction A2.

[0084] The method 100 comprises a fourth step 140 consisting of bringing the second strip 22 to the first strip 20 to form a row of cells 18 in the first direction A1, with the third strip 30 interposed, in the second direction A2, between the first strip 20 and the second strip 22, each tab 34 of the third strip 30 extending inside one of the cells 18.

[0085] Therefirst step 110 to the fourth step 140 can be repeated N times so as to form N rows of cells 18 along the second direction A2.

[0086] THE method 100 comprises a fifth step 150 consisting of heating the acoustic panel 12, in particular when the first strip 20, the second strip 22 and the third strip 30 are made of a thermosetting material. Heating the strips allows polymerization of the strips allowing the fixing of the strips together. Step v can be carried out with the strips arranged on a tool having a curvature so as to impart a curvature to the strips and therefore to the acoustic panel.

[0087] Alternatively, when each first strip 20 and second strip 22 is made of a metallic material, the fifth step 250 may consist of crosslinking an adhesive deposited between each third strip 30 and the adjacent first strip 20 and between each third and the adjacent second strip 22, for example by heating the acoustic panel 12 formed. The method 100 may thus comprise a subsidiary step consisting of depositing a layer of adhesive on each side of the third strip 30 in the second direction A2. This subsidiary step may in particular be carried out between the second step 120 and the third step 130.

[0088] The invention is not limited to the examples described above and is susceptible to numerous variations.

[0089] According to a variant not shown, the passage 36 delimited by each tab 34 is an opening with closed contours formed in the tab 34. Thus, each end edge of each tab 34 is joined, in the second direction A2, with one of the first ridge 20a of the first strip 20 and the first ridge 22a of the second strip 22 delimiting the associated cell 18.

[0090] According to a variant not shown, the third strip 30 comprises three or more tabs 34 extending inside one of the cells 18, transversely to the third direction A3 of the cell 18. The passages 36 delimited in whole or in part by two adjacent tabs 34 in the third direction A3 are offset relative to each other in a direction transverse to the third direction A3.

Claims

1. An acoustic panel (12) for a turbine engine, the acoustic panel (12) comprising at least: - a first strip (20) and a second strip (22), corrugated, each comprising an alternation, according to a first direction (A1), first ridges (20a, 22a) and second ridges (20b, 22b) connected by sidewalls (20f, 22f), said first strip (20) and said second strip (22) being joined to each other according to a second direction (A2) transverse to the first direction (A1), so as to form a plurality of cells (18) each delimited, in the second direction (A2), by a first ridge (20a) of the first strip (20) and a first ridge (22a) of the second strip (22), each cell extending according to a third direction (A3) transverse to the first direction (A1) and to the second direction (A2), - a third strip (30) interposed, in the second direction (A2), between the first strip (20) and the second strip (22), the third strip (30) comprising a first lateral wall (32) bearing, in the second direction (A2), on the first strip (20), the third strip (30) further comprising at least one tab (34) which extends inside one of the cells (18), at least partially transversely to the third direction (A3) of the associated cell, said at least one tab (34) being connected, at a first end edge in the second direction (A2), to the first lateral wall (32), said at least a tab (34) delimiting all or part of a passage (36) in the third direction (A3) inside the associated cell, the acoustic panel being characterized in that the third strip (30) comprises a plurality of tabs (34) offset from each other in the third direction (A3) of the associated cell (18), and in that the passages (36) totally or partially delimited by consecutive first tab (34) and second tab (34) in the third direction (A3) are offset from each other in a direction transverse to the third direction (A3) of the associated cell (18).

2. The acoustic panel (12) according to claim 1, wherein the passage (36) is delimited by a free edge of the tab (34) and one amongst the first ridge (20a) of the first strip (20) and the first ridge (22a) of the second strip (22), delimiting the associated cell (18).

3. The acoustic panel (12) according to claim 1, wherein the passage (36) is an opening with closed contours formed in the tab (34).

4. The acoustic panel (12) according to any one of the preceding claims, wherein each cell (18) has a section transverse to the associated third direction (A3) which is hexagonal, and wherein said at least one tab (34) comprises a central portion (34a) which extends, in the second direction (A2), between the first ridges (20a, 22a) of the first strip (20) and of the second strip (22), which delimit the associated cell (18), and two lateral portions (34b) each extending, in the second direction (A2), between sidewalls (20f, 22f) of the first strip (20) and of the second strip (22), opposite one another in the second direction (A2), which delimit the associated cell.

5. The acoustic panel (12) according to any one of the preceding claims, wherein the first lateral wall (32) of the third strip (30) comprises an alternation, in the first direction (A1), of first ridges (32a) and second ridges (32b) connected by sidewalls (32f), each first ridge (32a) and second ridge (32b) of the first lateral wall (32) respectively bearing, in the second direction (A2), on one of the first ridges (20a) and one of the second ridges (20b) of the first strip (20).

6. The acoustic panel (12) according to any one of the preceding claims, the third strip (30) further comprising a second lateral wall (38) bearing, according to the second direction (A2), on the second strip (22), said at least one tab (34) being connected, at a second end edge in the second direction (A2), to the second lateral wall (38).

7. The acoustic panel (12) according to any one of the preceding claims, wherein each second ridge (32b) of the first lateral wall (32) of the third strip (30), and where appropriate each second ridge (38b) of the second lateral wall (38) of the third strip (30), is clamped in the second direction (A2) between one of the second ridges (20b) of the first strip (20) and one of the second ridges (22b) of the second strip (22).

8. A method for manufacturing (100) an acoustic panel (12) according to any one of the preceding claims, comprising the steps of: i providing the corrugated first strip (20) and second strip (22) each comprising the plurality of first ridges (20a, 22a) and second ridges (20b, 22b) connected by sidewalls (20f, 22f), ii providing the third strip (30) comprising said at least one tab (34), iii positioning the first lateral wall (32) of the third strip (30) bearing on the first strip (20) according to the second direction (A2), iv joining the second strip (22) to the first strip (20) to form the plurality of cells (18), with the third strip (30) interposed, in the second direction (A2), between the first strip (20) and the second strip (22), said at least one tab (34) extending inside one of the cells (18) Wherein the first strip (20), the second strip (22) and the third strip (30) are preformed before steps iii) and iv).

9. The manufacturing method (100) according to claim 8, claims 5 and 6 applying, wherein step ii includes the subsidiary steps: a2 providing a third strip (30) having a planar shape, b2 forming the bend lines (J, M) delimiting each first ridge (32a, 38a) and second ridge (32b, 38b) of the first lateral wall (32) and of the second lateral wall (38) of the third strip (30), c2 forming at least one pair (K) of bend lines (K1, K2) on the third strip (30), each bend line (K1, K2) of said pair (K) delimiting one of the end edges in the second direction (A2) of said at least one tab (34), the bend lines (K1, K2) of said pair (K) being joined at each first ridge (32a, 38a) of the first lateral wall (32) and of the second lateral wall (38), d2 making a cutout in the third strip (30) intended to form the passage (36) delimited totally or partially by said at least one tab (34), e2 bending the first lateral wall (32) and the second lateral wall (38) so that each has a corrugated shape with an alternation of first ridges (32a, 38a) and second ridges (32b, 38b) connected by sidewalls (32f, 38f), f2 bending said at least one tab (34) with respect to the first lateral wall (32), g2 bending the second lateral wall (38) with respect to said at least one tab (34) and to the first lateral wall (32) so that each second ridge (38b) of the second lateral wall (38) is opposite one of the second ridges (32b) of the first lateral wall (32).

10. The method according to the preceding claim, wherein steps e2, g2 and f2 are carried out by an automatic press brake.