OPTIMIZED SOUND ABSORPTION PLATE FOR AN AIRCRAFT TURBOCHARGER

Description

Technical field of the invention

[0001] The invention relates to an acoustic attenuation panel for an aircraft turbomachine, and a method for manufacturing such a panel. Technical background

[0002] The prior art includes documents EP-2.478.202-B1, US-9.514.734-B1, WO-2006 / 107.533-A2, US-2012 / 168248-A1 and EP-2.788.601-B1.

[0003] Acoustic attenuation panels are widely used in turbomachinery for cladding areas subject to significant gas passages, such as an air inlet, a fan casing or a secondary flow duct located downstream of the fan through which air flows, or an exhaust nozzle or exhaust cone of the turbomachine, better known by the Anglo-Saxon acronym "plug", subject to a passage of exhaust gas.

[0004] These acoustic attenuation panels are generally made in the form of sandwiches comprising at least an outer skin, an inner skin, and a core sandwiched between these two skins. The core consists of a plurality of tubular polygonal cells, each oriented perpendicular to the outer and inner skins. These cores are typically made of a hexagonal honeycomb material. These cells are hollow along their entire length.

[0005] The height of the cells is crucial to the panel's ability to absorb sound waves. The first layer, also called the permeable acoustic layer, has numerous holes opening into the cells. The second layer is called the acoustically reflective layer. Sound wave absorption has been shown to be optimal when the height between these two layers of cells is approximately one-quarter of the wavelength of the sound wave being treated.

[0006] Currently, for reasons of integration and compactness, it is desirable to produce acoustic attenuation panels that are thinner than conventional panels. However, it is not possible to reduce the cell height without resulting in a loss of the panel's ability to absorb sound waves at the target frequencies.

[0007] There is therefore a real need for a sound attenuation panel that is thinner than a conventional panel but still maintains the same level of sound attenuation. Summary of the invention

[0008] The invention satisfies this need by proposing an acoustic attenuation panel in which the cells are of reduced height and each provided with at least one internal partition allowing the sound wave to have a path in the cell which is the same length as a conventional cell.

[0009] To this end, the invention proposes an acoustic attenuation panel for an aircraft turbomachine, said panel comprising a first skin, a second skin, and a core sandwiched between the first and second skins, said core comprising a plurality of tubular polygonal cells, each having an orientation perpendicular to the first and second skins, each cell comprising an internal cavity communicating with at least one hole formed in said first skin and delimited by lateral walls extending between the first and second skins and perpendicular to the first and second skins, these lateral walls having a first height equal to a distance between the first and second skins, characterized in that each polygonal cell further comprises at least one internal partition within its cavity,This internal partition extends substantially from the first skin perpendicularly to the first and second skins along a second height lower than the first height, and transversely into the cavity between two lateral walls of the cell, this internal partition dividing the cavity into at least two adjacent pockets and delimiting, between a free end of said partition and the second wall, a passage allowing the two adjacent pockets to communicate with each other and with said hole.

[0010] The acoustic attenuation panel according to the invention allows sound waves to travel the same distance as a conventional panel by directing the wave along two pockets of equal length. This configuration allows the panel to have cells with a first height half that of a conventional panel, while maintaining the same acoustic absorption capacity.

[0011] According to other panel characteristics: said at least one internal partition extends transversely between internal faces of two substantially opposite lateral walls of the cell, said at least one internal partition extends transversely between a junction edge of the first and second lateral walls and a third lateral wall substantially opposite the first and second lateral walls, said at least one internal partition extends transversely between a junction edge of the first and second lateral walls and a junction edge of the third and fourth lateral walls, each polygonal cell is a regular polygonal cell having a central axis and it comprises at least two partitions joined along said central axis, each polygonal cell is a hexagonal cell, each cell comprises as many internal partitions joined along the central axis as lateral walls,Each cell has an even number of lateral walls, and the internal partitions extend transversely between said axis and the edges of junction of the lateral walls, delimiting as many interconnected pockets as there are lateral walls. Each cell has an even number of lateral walls, half as many partitions as lateral walls, and internal walls of the same first height as the lateral walls, which alternate around the central axis with said partitions so as to delimit pairs of adjacent communicating pockets. Each pair of communicating pockets is isolated from the other pairs of communicating pockets and communicates with a hole in the first skin. The number of communicating pocket pairs is half the number of lateral walls. The first height is equal to one-eighth of a wavelength of a sound to be attenuated. The cells of the soul, the lateral walls,and at least one internal partition are obtained by an additive manufacturing process. The core cells and side walls are obtained by extruding a plastic material, at least one internal partition is also obtained by extruding a plastic material, and at least one internal partition is welded into each cell. The core cells are obtained by supplying a conventional honeycomb material in which at least one insert is placed, forming at least one partition. The first height is between 20 and 50 mm, the second height is greater than half the first height and at least 5 mm less than or equal to the first height.

[0012] The invention also relates to a method for manufacturing a sound attenuation panel of the type described above, characterized in that it comprises: a first step of manufacturing a first skin, a second step of manufacturing a second skin, a third step of manufacturing the core by additive manufacturing, by extrusion and welding, or by supplying a conventional honeycomb material in which at least one insert is placed forming at least one partition, a fourth step of fixing the first and second skins to the core by welding, brazing, or gluing, a fifth step of drilling the first skin making holes in said first skin which each open into a pocket of a polygonal cell of the core.

[0013] The invention finally relates to a turbomachine, characterized in that it comprises at least one gas flow vein delimited by at least one wall comprising an attenuation panel of the type described above. Brief description of the figures

[0014] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the attached drawings in which: [ Fig. 1 ] There figure 1 is a schematic view of the locations of acoustic attenuation panels in a turbomachine and its nacelle; [ Fig. 2 ] There figure 2 is a perspective view of a conventional acoustic attenuation panel; Fig. 3 ] There figure 3 is a perspective view of the core of a conventional acoustic attenuation panel; Fig. 4 ] There figure 4 is a perspective view of a hexagonal cell of the core of an acoustic attenuation panel according to the invention; [ Fig. 5 ] There figure 5 is another perspective view of a hexagonal cross-section cell of the core of an acoustic attenuation panel according to the invention; [ Fig. 6 ] There figure 6is a perspective view of a first end of a hexagonal cell of the core of an acoustic attenuation panel according to the invention; [ Fig. 7 ] There figure 7 is a perspective view of a second end of a hexagonal cell of the core of an acoustic attenuation panel according to the invention; [ Fig. 8a ] There figure 8a is a top view of a first embodiment of the first end of a hexagonal cell of the core of an acoustic attenuation panel according to the invention; [ Fig. 8b ] There figure 8b is a top view of a second embodiment of the first end of a hexagonal cell of a core of an acoustic attenuation panel according to the invention; [ Fig. 8c ] There figure 8c is a top view of a third embodiment of the first end of a hexagonal cell of a core of an acoustic attenuation panel according to the invention; [ Fig. 8d ] There figure 8d is a top view of a fourth embodiment of the first end of a hexagonal cell of a core of an acoustic attenuation panel according to the invention; [ Fig. 9 The figure is a perspective view of the hexagonal cross-section cell of the figure 8d ; Fig. 10 ] There Figure 10 is a perspective view of a rectangular-section cell of the core of an acoustic attenuation panel according to the invention; [ Fig. 11 ] There figure 11 is a block diagram illustrating the steps of a first embodiment of a manufacturing process for an acoustic attenuation panel according to the invention; [ Fig. 12 ] There figure 12 is a block diagram illustrating the steps of a second embodiment of a manufacturing process for an acoustic attenuation panel according to the invention. Detailed description of the invention

[0015] We represented at the figure 1schematically a turbomachine 10. As is known, the turbomachine 10 comprises, from upstream to downstream, an air inlet 12, a casing 14, a secondary flow channel 16 delimited by an internal wall 20 and an external wall 18, and a primary flow channel 22 which is delimited by an exhaust casing 24 and by an exhaust cone 26, also known by the Anglo-Saxon acronym "plug".

[0016] The air inlet 12 is traversed by an incoming airflow F, the secondary flow channel 16 is traversed by a secondary airflow S and the nozzle 22 allows the ejection of a primary gas flow P.

[0017] The rotating parts of the engine are significant sources of noise. Noise from the fan propagates upstream against the flow F in the air inlet 12 or downstream in the direction of the flow S in the secondary duct 16. Noise from the turbine propagates in the flow P through the nozzle 22. To mitigate this, the air inlet 12, the engine casing 14, the secondary duct 16, and the nozzle 22 can have their walls covered with acoustic attenuation panels. Similarly, the air inlet 12, the walls 18 and 20 of the secondary duct, the exhaust casing 24, and the exhaust cone 26 can be covered with acoustic attenuation panels 28.

[0018] As illustrated by the figure 2, such a panel 28 is generally made in the form of a sandwich comprising in its simplest expression at least a first skin 30 oriented towards the side of the incoming airflow F, the primary flow P or the secondary flow S, a second skin 32, and at least one core 34. Of course, the sandwich can include other intermediate layers and in particular other cores superimposed on the core 34.

[0019] The first skin 30 has holes or perforations 38 and is called a permeable acoustic skin. The second skin 32 is closed and is called an acoustically reflective skin.

[0020] The core 34 comprises a plurality of tubular polygonal cells 36, each oriented along an axis A perpendicular to the first and second skins. This core 34 is generally made in the form of a plate of honeycomb material with hexagonal cells 36, which are hollow along their entire height H, this height H corresponding to the distance between the first and second skins 30, 32. The first skin 30 has a plurality of holes or perforations 38 that open into the cells 36. Sound waves therefore enter the cells 36 through these holes or perforations 38.

[0021] As illustrated by the figure 3The height H of the cells 36 is a key parameter that determines the panel 28's ability to absorb sound waves. It has been shown that sound wave absorption is optimal for a conventional panel 28 when the cells 36 have a height H corresponding approximately to one-quarter of the wavelength λ of the sound wave to be processed.

[0022] However, for reasons of integration and compactness, it is desirable to produce acoustic attenuation panels that are thinner than conventional panels. However, it is not possible to reduce the height of the cells 36 without altering the frequency behavior of the panel 28. Indeed, any reduction in the height H of the core 34 results in shifting the panel's attenuation peak towards higher frequencies, which are then no longer within the target frequency range.

[0023] The capacity of a cell to absorb an acoustic wave of wavelength λ is directly dependent on the length of the path traveled by the acoustic wave within cell 36, that is to say, according to the above, a length corresponding to one-quarter of the wavelength, or λ / 4. However, it has also been observed that the length of this path does not necessarily have to be limited to a straight path, in this case along the height H of cell 36. In other words, the acoustic wave can be effectively absorbed as long as the total path length is close to λ / 4, but this length can be distributed along a non-straight path.

[0024] The invention therefore advantageously proposes an acoustic attenuation panel 28 that is thinner than a conventional panel while maintaining the same level of acoustic attenuation and the same target frequency range. The cells 36 of this panel are partially partitioned to distribute the path of the acoustic waves along a first height H1 of the cell but in at least two adjacent pockets, and in this case the first height H1 can therefore be reduced compared to a conventional cell.

[0025] A cell 36 for a panel according to the invention was represented at figures 4 to 7 And 9These figures represent a unit cell 36 sandwiched between a corresponding portion 30' of the first skin 30 and a corresponding portion 32' of the second skin 32, it being understood that the cells 36 are all obtained in a single manufacturing operation. The cell 36 shown here has a hexagonal cross-section, but it will be understood that this feature is not limiting to the invention, and the invention is applicable to any cell with a polygonal cross-section, that is to say, triangular, square, rectangular, pentagonal, octagonal, regular or irregular.

[0026] Each cell 36 has an internal cavity 40 which communicates with at least one of the holes 38 formed in the first skin 30 and which is delimited by lateral walls 42 extending between the first and second skins 30, 32 and perpendicular to the first and second skins 30, 32. These lateral walls 42 have a first height H1 equal to a distance between the first and second skins 30, 32.

[0027] According to the invention, each polygonal cell 36 further comprises at least one internal partition 44 inside the cavity 40. The internal partition 44 extends substantially towards the second skin 32 from the first skin 30, perpendicular to the first and second skins 30, 32, along a second height H2 that is less than the first height H1. It thus delimits a passage of third height H3 between the free end 46 of the partition 44 and the second skin 32.

[0028] At least one partition 44 extends transversely into the cavity 40 between two lateral walls 42 of the cell 36, whether between intermediate parts of the lateral walls 42, as shown in the Figure 10 or between edges 50 of junction of the lateral walls 42, as can be seen in Figures 4 to 8c .

[0029] Therefore, at least one partition 44 divides the cavity 40 into at least two adjacent pockets 52. The passage between the free end 46 of the partition 44 and the second wall 32 allows the two adjacent pockets 52 to communicate with each other and with the hole 38, as illustrated by the arrows that show the propagation C of sound waves on the figures 4 , 8a-8d And 9 .

[0030] On the Figure 10 , we have represented a group of four cells 36 of rectangular sections delimiting four cavities 40, each cavity 40 receiving a partition 44 of the type described previously.

[0031] The partitions 44 can extend transversely in various ways within the cavities 40. For example, as illustrated by the Figure 10 , each internal partition 44 extends transversely between internal faces 48 of two substantially opposite lateral walls 42 of the cell 36. This configuration is particularly suited to a cell 36 having an even number of lateral walls 42.

[0032] Alternatively (not shown), at least one internal partition 44 could extend transversely between a junction edge of the first and second lateral walls and a third lateral wall substantially opposite the first and second lateral walls. This configuration is particularly suited to a cell 36 having an odd number of walls, such as a triangular or pentagonal cell.

[0033] Alternatively, at least one internal partition 44 may extend transversely between a junction edge of first and second side walls 42 and another junction edge of third and fourth side walls 42.

[0034] A special case of this cell 36 configuration is that of a regular polygonal cell 36 having a central axis A.

[0035] In this case, cell 36 does not have one but at least two adjoining partitions 44 along the central axis A. Cell 36 can have as many adjoining internal partitions 44 along the central axis 44 as it has lateral walls 42, whether or not cell 36 has an even number of lateral walls 42.

[0036] The term "contiguous partitions" refers to at least two internal partitions 44 connected to each other at the central axis A of the tubular polygonal cell 36. For example, the figure 8cillustrates two internal partitions 44 (or in other words two half-partitions) connected to each other at the central axis A, the figure 8b illustrates four internal partitions 44 connected to each other at the central axis A and the figures 6, 7 , 8a And 9 illustrate six internal partitions 44 connected to each other at the central axis A. Each internal partition 44 of the adjoining partitions can extend in a transverse direction between internal faces 48 of two lateral walls 42, between two junction edges 50 or between a junction edge 40 and an opposite lateral wall.

[0037] This is, for example, the case with the configuration of hexagonal cell 36 of the figures 4 to 8a-8c where each partition 44 extends between the central axis A and a joining edge 50 of two of the lateral walls 42.

[0038] In the case of a cell 36 consisting only of identical internal partitions 44 and having an even number of lateral walls 42, as is the case of a hexagonal cross-section cell 36 such as that shown in figures 4 to 8a-8c , each partition 44 is aligned with another identical partition 44.

[0039] In the example shown here, the internal partitions extend transversely between the axis A and the edges 50 of junction of the side walls 40, delimiting as many pockets 52 communicating with each other as there are side walls 42.

[0040] In this case, each pocket 52 communicates with all the others and with hole 38.

[0041] Cell 36 can also include a smaller number of partitions 44 alternating with internal walls of the same height H1 as the lateral walls of cell 36 to delimit pairs of pockets 52 each associated with a hole 38.

[0042] This is the case with the configuration of the figures 8d And 9 , which represent a cell 36 comprising an even number of side walls 42, half as many partitions 44 as side walls 42, and internal walls 54 of the same first height H1 as the side walls 42, which alternate around the central axis A with said partitions 44.

[0043] In this way, the partitions 44 and the internal walls 54 delimit pairs of adjacent communicating pockets 52 (here three pairs of communicating pockets 52, since the cell 36 has a hexagonal cross-section).

[0044] Each pair of communicating pockets 52 is isolated from the other pairs of communicating pockets 52 and communicates with a hole 38 formed in the first skin 30. The cell 36 is therefore supplied by three holes 36. The pairs of communicating pockets 52 are in this case in number half less than the number of lateral walls 42.

[0045] Whatever embodiment is chosen here, and without limiting the invention, the sound waves therefore travel in cell 36 along a path C which is approximately twice the first height H1 of the lateral walls 42 of the cell 36 and its cavity 40. Consequently, this path must, in order to satisfactorily attenuate the sound waves, be of a length λ / 4 equal to a quarter of the emitted wavelength, we can therefore propose a cell with a first height H1 equal to one-eighth of the wavelength λ of the sound to be attenuated, i.e. λ / 8.

[0046] As an example, the first height H1 is between 20 and 50 mm.

[0047] The second height H2, meanwhile, is greater than half of the first height H1 and at least less than or equal to the first height H1 by 5mm.

[0048] Therefore, one can preferentially benefit from a 34 core that is half as thick as a conventional 34 core.

[0049] The 34 core can be obtained in different ways depending on its material.

[0050] If it is metallic or thermoplastic, the cells 36 of the core 34, the side walls 42, and at least one internal partition 44, or even the internal walls 54, can be obtained by an additive manufacturing process.

[0051] However, for a thermoplastic material it is more economical for the core cells 34 and the side walls 42 to be obtained in one step by extrusion of a plastic material, for at least one internal partition 44 or even at least one internal wall 54 to be obtained also but independently in another step by extrusion of a plastic material, and then for at least one internal partition 44 and / or at least one internal wall 54 to be added and welded into each cell 36.

[0052] The cells 36 of the core 34 can still be obtained by supplying a conventional honeycomb material in which at least one insert is placed forming at least one partition 44.

[0053] In this configuration, as illustrated by the Figures 11 And 12 , we can manufacture an attenuation panel 28 of the type described above according to a process comprising a first step ET1 of manufacturing the first skin 30.

[0054] In a second step ET2, the second skin 32 is manufactured.

[0055] In a third step ET3 the core 34 is manufactured by additive manufacturing, by extrusion and welding, or by supplying a conventional honeycomb material in which inserts forming the internal partitions 44 are placed.

[0056] The process also includes a fourth step ET4 of fixing the first and second skins 30, 32 to the core 34 by welding, brazing, or gluing.

[0057] It should be noted that the fourth step can be carried out in different ways. It is possible to transfer the first and second skins 30, 32 onto the core 34, or to transfer the core 34 first onto one of the two skins 30, 32, and then transfer the other skin 32 or 30 onto the core 34.

[0058] In a first variant of this process, as shown in the figure 11 , this follows the numerical order of the steps and it is therefore at the end of the fourth step ET4 that the process includes a fifth step ET5 of drilling or punching the first skin 30, which makes it possible to make in said first skin 30 the holes 38 which each open into a pocket 52 of a polygonal cell 36 of the core 34.

[0059] Alternatively, the process may involve an ET5 step of drilling or punching the first skin 30 during the ET4 step before the final assembly of the two skins 30, 32, this drilling or punching being able to take place with the skin 30 assembled to the core 34 if it is the first to be assembled there, or being able to take place on the bare skin 30 alone, prior to its assembly with the core 34 already assembled to the skin 32.

[0060] Regardless of the variant chosen, it is not necessary to seek to position the holes 38 of the first skin 30 in relation to the cells 36. It is sufficient that the drilling or punching pattern is regular and that the pitch between the holes 38 is correctly defined so that the drilling of the skin 30 statistically generates enough holes 38 placed appropriately to communicate with a sufficient number of pockets 50.

[0061] The invention thus makes it possible to have a turbomachine or a turbomachine nacelle 10 comprising at least one gas flow path F, P, S delimited by at least one wall comprising a panel 28 of the type described above. The use of such panels 28 makes it possible to use them in more compact turbomachines.

Claims

1. A sound attenuation panel (28) for an aircraft turbomachine or turbomachine nacelle (10), said panel (28) comprising a first skin (30), a second skin (32), and a core (34) sandwiched between the first and second skins (30, 32), said core comprising a plurality of tubular polygonal cells (36) which each have an orientation (A) perpendicular to the first and second skins (30, 32), each cell (36) comprising an internal cavity (40) which communicates with at least one hole (38) formed in said first skin (30) and which is delimited by side walls (42) extending between the first and second skins (30, 32) and perpendicularly to the first and second skins (32), these side walls (42) having a first height (H1) equal to a distance between the first and second skins (30, 32), each polygonal cell (36) further comprises at least one internal partition (44) inside its cavity (40), this internal partition (44) extending from the first skin (30) perpendicularly to the first and second skins (30, 32) at a second height (H2) less than the first height (H1), and transversely in the cavity (40) between two side walls (42) of the cell (36), this internal partition (44) dividing the cavity (40) into at least two adjacent pockets (52) and delimiting between a free end (46) of said partition (44) and the second skin (32) a passage allowing said at least two adjacent pockets (52) to communicate with each other and with said hole (38), each polygonal cell (36) is a regular polygonal cell having a central axis (A) and characterised in that it comprises at least two partitions (44) joined along said central axis (A).

2. The sound attenuation panel (28) according to claim 1, characterised in that said at least two partitions (44) extend transversely between internal faces (48) of two opposite side walls (42) of the cell (36).

3. The sound attenuation panel (28) according to claim 1, characterised in that said at least two partitions (44) extend transversely between an edge joining first and second side walls and a third side wall opposite the first and second side walls.

4. The sound attenuation panel (28) according to claim 1, characterised in that said at least two partitions (44) extend transversely between an edge (50) joining first and second side walls (42) and an edge (50) joining third and fourth side walls (42).

5. The sound attenuation panel (28) according to any one of the preceding claims, characterised in that each polygonal cell (36) is a hexagonal cell.

6. The sound attenuation panel (28) according to any one of the preceding claims, characterised in that each cell (36) comprises as many internal partitions (44) joined along the central axis (A) as there are side walls (42).

7. The sound attenuation panel (28) according to any one of the preceding claims, characterised in that each cell (36) comprises an even number of side walls (42) and in that the internal partitions (44) extend transversely between said axis (A) and the edges (50) joining the side walls (42), delimiting as many pockets (52) communicating with one another as there are side walls (42).

8. The sound attenuation panel (28) according to any one of the preceding claims, characterised in that each cell (36) comprises an even number of side walls (42), half as many partitions (44) as side walls (44), and internal walls (54) of the same first height (H1) as the side walls (44), which alternate about the central axis (A) with said partitions (44) so as to delimit pairs of adjacent communicating pockets (52), each pair of communicating pockets (52) being isolated from the other pairs of communicating pockets (52) and communicating with a hole (38) in the first skin (30), the number of pairs of communicating pockets (52) being half the number of side walls (42).

9. The sound attenuation panel (28) according to one of the preceding claims, characterised in that the first height (H1) is equal to one eighth of a wavelength of a sound to be attenuated.

10. The sound attenuation panel (28) according to one of the preceding claims, characterised in that the first height (H1) is between 20 and 50 mm.

11. The sound attenuation panel (28) according to one of the preceding claims, characterised in that the second height (H2) is greater than half the first height (H1) and at least 5 mm less than or equal to the first height (H1).

12. A method of manufacturing a sound attenuation panel (28) according to one of the preceding claims, characterised in that it comprises: - a first step (ET1) of manufacturing a first skin (30), - a second step (ET2) of manufacturing a second skin (32), - a third step (ET3) of manufacturing the core (34) by additive manufacturing, by extrusion and welding, or by supplying a conventional honeycomb material in which at least one insert forming said at least one partition (44) is arranged, - a fourth step (ET4) of fixing the first and second skins (30, 32) to the core (34) by welding, brazing or gluing, and - a fifth step (ET5) of drilling the first skin (30), producing holes (38) in said first skin (30), each of which opens statistically into a pocket (52) of a polygonal cell (36) of the core.

13. A turbomachine (10), characterised in that it comprises at least one gas flow duct (F, P, S) delimited by at least one wall comprising a sound attenuation panel (28) according to one of claims 1 to 11.