BE1030361A1 - DAMPING SHELL FOR TURBOMACHINE, ASSEMBLY COMPRISING THE SHELL AND A BLADE, ROTARY ASSEMBLY, COMPRESSOR AND ASSOCIATED MANUFACTURING METHOD - Google Patents

Abstract

The present invention relates to a shell (40) configured to be mounted on a blade support element of a turbomachine and capable of defining a profile of a vein for a flow of fluid through the turbomachine, the shell (40 ) comprising: - a central portion (90) comprising a recess (41) to allow the placement of the shell (40) around a blade (30), and - a peripheral portion (92) at least partially surrounding the central portion (90), the central portion (90) comprising an elastomeric material to damp vibrations of the blade (30).

Description

Damping shell for a turbomachine, assembly comprising the shell and a blade, rotating assembly, compressor and associated manufacturing process

Technical area

[0001] The present invention relates to a hull configured to be mounted on a turbomachine. The present invention also relates to a method of manufacturing such a shell.

Prior art

[0002] EP 3 683 450 describes a platform which can be mounted on the blisk of a turbomachine. The platform includes a recess for its insertion around a blade. This platform covers the surface of the rim of the turbomachine so as to define a profile of a vein for fluid flow through the turbomachine. This platform allows greater tolerance of rim geometry error. Indeed, regardless of the exact shape of the rim, it is enough to cover it with a platform that has a shape of the desired surface.

[0003] The blade of a rotor blade is subjected to synchronous type vibrations with respect to the rotation speed of the engine as well as to asynchronous vibrations. These blade vibrations impact the aerodynamic design of the blades and therefore move away from the aerodynamically ideal blade. In addition, if blade vibration phenomena are not properly taken into account, they can lead to blade breakage.

Summary of the invention

One of the aims of the present invention is to propose a part for a turbomachine to reduce blade vibration problems, this part not requiring significant modification of the turbomachine as such.

[0005] For this purpose, the invention proposes a shell configured to be mounted on a blade support element of a turbomachine and capable of defining a profile of a vein for a flow of fluid through the turbomachine, the shell comprising: - a central portion comprising a recess to allow the placement of the shell around a blade, and - a peripheral portion at least partially surrounding the central portion, the central portion comprising an elastomeric material to damp vibrations of the 'dawn.

[0006] Thanks to the present invention, the central portion is capable of damping vibrations of the blade. The central portion, made of elastomeric material, is in direct contact with the blade. The damping system is therefore located as close as possible to the vibrations, which ensures good efficiency of

Damping of blade vibrations. The central portion is capable of absorbing all types of vibrations, for example in bending and/or torsion.

[0007] The exterior surface of the shell makes it possible to define a profile of a vein for a flow of fluid through the turbomachine.

Thus, when the hull is mounted on the rim of a turbomachine, the exact shape of the rim does not matter as long as the hull has a desired aerodynamic shape. The rim corresponds to part of a disc and is particularly suitable for blisks. Preferably,

The recess of the central portion is open, preferably on the downstream side.

Then, the hull can be placed around a blade by a relative movement between the hull and the blade which is essentially parallel to the main axis A of the bladed disk carrying the hull.

[0008] According to particular embodiments, the shell according to the invention may comprise one or more of the following characteristics:

[0009] - the peripheral portion is made of metal or composite material.

[0010] Such materials allow the peripheral portion to have a solid structure.

[0011] - the elastomer material of the central portion is of the silicone or rubber type.

[0012] Such materials provide excellent damping quality through the central portion.

[0013] - the recess includes a bottom to come into abutting contact with the blade.

[0014] The invention also relates to an assembly for a turbomachine, comprising: - a shell as described above; - a blade inserted in the recess in the central portion of the hull and in contact with the central portion, the blade having a total length H.

[0015] According to particular embodiments, the assembly according to the invention may comprise the following characteristic:

[0016] - the central portion has a thickness greater than or equal to 7% of the total length H of the blade, preferably greater than or equal to 9%.

[0017] Such thicknesses of the shell ensure an even greater reduction in vibrations. According to these particular embodiments, the absorbent zone (and therefore the central portion) has a thickness to absorb vibrations even more effectively. The inventors thus recommend a thickness (or height) of the central portion which is greater than or equal to 7% of the total length H of the blade.

This seems to be all the more preferred as at the very embedding of the blade, there is little vibration, in comparison with what happens further away from the disc or the rim of the disc. Preferably, the inventors recommend using a blade elongated downwards (or towards the disk) by 5% to 10% compared to a standard size without using a shell according to the invention. Thus, when covered with the shell which would have a thickness essentially equal to this elongation or of a close dimension, there remains a vein of 100% of the height initially planned or almost.

[0018] The invention also relates to a rotating assembly of a turbomachine, comprising: - an assembly as described above; - a bladed disk extending around an axis and comprising a rim having a rim surface extending around the axis, the shell of the assembly being attached to the bladed disk, the blade of the assembly comprising a foot fixed to the rim and extending radially from the rim surface.

[0019] According to particular embodiments, the rotating assembly according to the invention may comprise one or more of the following characteristics:

[0020] - the shell comprises a first fixing element configured to cooperate with the rim so as to hold the shell radially relative to the rim.

[0021] - the first fixing element is configured to hold the hull axially relative to the blisk.

[0022] This first fixing element then makes it possible to reinforce the axial support of the hull in relation to the blisk.

[0023] - the rim comprises a second fixing element configured to cooperate with the first fixing element so as to hold the shell radially relative to the rim.

This second fixing element makes it possible to improve the radial retention of the hull relative to the blisk.

[0025] - the rotating assembly further comprises a ring comprising a third fixing element and a fourth fixing element, the third fixing element being configured to hold the ring radially relative to the rim, the fourth fixing element being configured to hold the shell radially relative to the rim.

[0026] The ring thus makes it possible to improve the radial support of the hull in relation to the blisk.

[0027] - the rotating assembly comprises at least two shells, each of them comprising a first side edge and a second side edge both extending substantially axially, the first side edge of a first shell being intended to overlap the second side edge of a second adjacent shell.

[0028] This overlap between two adjacent shells makes it possible to reduce fluid leaks between two shells.

[0029] - the rotating assembly comprises at least one secondary damper mechanically coupled to the peripheral portion of the shell to damp vibrations of the blade.

[0030] Vibrations are further damped by the vibration/friction of the secondary shock absorber. In particular, the secondary damper is particularly effective when the blade begins to experience significant vibrations which are felt up to the secondary damper.

[0031] The invention also relates to a turbomachine compressor comprising a rotor comprising a rotating assembly as described above.

[0032] The invention also relates to a method of manufacturing a shell as described above, comprising the following steps: - manufacturing the peripheral portion by molding, the peripheral portion having a receiving space, - arrangement of the central portion in the reception space, - securing of the central portion to the peripheral portion.

[0033] According to particular embodiments, the manufacturing process according to the invention may comprise the following characteristic:

[0034] - the joining step is ensured via composite material inserts in the central portion and/or via glue.

Brief description of the figures

[0035] Other characteristics and advantages of the invention will appear on reading the detailed description which follows, for an understanding of which reference will be made to the appended figures among which: - Figure 1 is a perspective view of a hull according to the invention. - Figure 2 is a schematic perspective view of a rotating assembly according to the invention; - Figure 3 is a partial schematic exploded perspective view of a rotating assembly according to the invention; - Figures 4a, 4b and 4c are partial schematic views in sections along a plane including the axis A representing different embodiments of a rotating assembly according to the invention.

Modes of carrying out the invention

The present invention is described with particular embodiments and references to figures but the invention is not limited by these. The drawings or figures described are only schematic and are not limiting. In addition, the functions described may be performed by structures other than those described in this document.

[0037] In the context of this document, the terms “first” and “second” serve only to differentiate the different elements and do not imply an order between these elements.

[0038] In the figures, identical or similar elements may bear the same references.

[0039] Figure 1 shows a possible embodiment of a shell 40 according to the invention.

The shell 40 comprises a central portion 90 and a peripheral portion 92. The central portion 90 comprises a recess 41 configured to allow the placement of the shell 40 around one of the blades 30. The peripheral portion 92 at least partially surrounds the central portion 90.

The central portion 90 comprises an elastomeric material and makes it possible to damp vibrations of the blade 30. Advantageously, the elastomeric material of the central portion 90 is of the silicone or rubber type.

In certain cases, the central portion 90 is capable of transmitting at least partially vibrations from the blade 30 to the peripheral portion 92.

[0042] The recess 41 makes it possible to match the shape of the side walls 32 of the blade 30. As illustrated in Figure 1, this recess 41 is preferably open, preferably on the downstream side.

Preferably, the peripheral portion 92 has a shear modulus strictly greater than that of the central portion 90. The shear modulus of the peripheral portion 92 is for example 100 times, advantageously 200 times, more advantageously 1000 (thousand) times, or even more advantageously 10,000 (ten thousand) times the shear modulus of the central portion 90.

[0044] According to a preferred embodiment, the peripheral portion 92 is made of metal or composite material.

[0045] Figure 2 shows a rotating assembly 100 of a turbomachine according to the invention.

The rotating assembly 100 comprises a bladed disk 10 around an axis A. The axis A is centered relative to the bladed disk 10 and extends substantially parallel to a direction 70 of fluid flow in the turbomachine .

[0047] The invention is preferentially applied to a rotor stage, as illustrated in the figures (even if the invention could be applied to a stator stage). In the case of a rotor stage, as illustrated in the figures, the bladed disk 10 is a rotating bladed disk. The blades 30 on the bladed disk 10 extend radially towards the outside of the turbomachine.

The bladed disk 10 comprises a circular rim 20 extending around the axis À. The rim 20 notably comprises a rim surface 21 located radially outwards. The rim surface 21 extends around the axis A.

The bladed disk 10 comprises in particular a blade 30 and in particular a plurality of blades 30. According to the embodiment shown in Figures 2 and 3, the blade 30 extends radially outwards, from the rim surface 21. Each of the blades 30 comprises a foot 31. According to the embodiment shown on the

Figures 2 and 3, the blades 30 are fixed by the foot 31 on the rim 20 and in particular on the rim surface 21. The blades 30 also comprise a main body 35. The main body 35 comprises side walls 32 intended to be in contact with the fluid flowing in the turbomachine. The recess 41 is configured to match the shape of the side walls 32 of the blade 30. Thus, it is particularly easy to position the shell 40 around the blade 30.

The blade 30 has a total length H. That is to say the entire base 31 and the main body 35 has a length H. When the blade 30 is fixed on the bladed disk 10, the length H is measured in the radial direction of the blisk 10.

The blades 30 are preferably fixed to the rims 20 by welding and in particular by friction. The bladed disc 10 is then a one-piece disc but the invention also relates to discs comprising blades attached to the rim and not integrated into it.

Such a configuration will be called an assembly, as explained below.

[0052] In the example illustrated in Figure 2, the rotating assembly 100 comprises a plurality of shells 40 according to the invention. The shells 40 are configured to be mounted on a blade support element of the turbomachine. According to the embodiment where the bladed disk 10 is a rotating bladed disk, the blade support element is the rim 20.

[0053] These shells 40 are assembled to the bladed disk 10 so as to define a profile of a fluid flow path passing through the turbomachine. The shells 40 are assembled externally with respect to the rim surface 21, around the axis À and preferably essentially parallel to the direction 70 of flow of the fluids passing through the turbomachine.

[0054] The rotating assembly 100 illustrated in Figure 2 comprises three bladed disks 10 arranged one after the other in the axial direction but it could also include one, two or more than three without leaving the frame of the invention.

[0055] Figure 3 shows the blisk of Figure 2 in partial exploded view.

The shell 40 in Figure 3 comprises a main body 52. The main body 52 comprises an upstream side 43, a downstream side 44, an interior side 45, an upper side or upper surface 46, a first lateral side 47 comprising a first lateral edge 49 and a second lateral side 48 comprising a second lateral edge 50. The first 47 and the second lateral edge 48 connect the upstream 43 and downstream 44 sides together.

The lower side 45 is intended to be in contact over essentially its entire surface with the rim surface 21. This contact between the shell 40 and the rim 20 makes it possible to improve the mechanical connection between the shell 40 and the rim 20. The upper side 46, opposite the lower side 45, defines the flow path of the fluid passing through the turbomachine.

[0058] When the shell 40 is mounted on the turbomachine, the first side edge 49 and the second side edge 50 both extend substantially axially.

[0059] According to one embodiment where the rotating assembly 100 comprises at least two shells 40, the first side edge 49 of a first shell 40 is intended to overlap the second side edge 50 of a second adjacent shell 40 (see for example figure 2).

The main body 52 comprises a central portion 90 and a peripheral portion 92 as described above. The central portion 90 is in contact with the blade 30 during normal use of the rotating assembly 100.

[0061] As illustrated in Figure 3, the recess 41 passes through on either side the central portion 90 of the shell 40 from the upper side 46 to the lower side 45. The recess 41 begins here on the downstream side 44 and continues towards the upstream side 43 without nevertheless reaching it. It ends with a bottom 42. The bottom 42 makes it possible to act as a stop against the blade 30, in particular once the shell 40 is assembled on the bladed disc 10 around the blade 30. The bottom 42 thus makes it possible to maintain the shell 40 on the blade 30 in an axial direction, in particular in the direction 70 of fluid flow.

The shell 40, in particular its central portion 90, must be sufficiently thick to absorb vibrations from the blade 30. The central portion 90 has a thickness E greater than or equal to 7% of the total length

H of the blade 30, preferably greater than or equal to 9% of the total length

H of Paube 30. In other words, when the blade 30 is arranged in the recess 41 of the shell 40, less than 92.5%, preferably less than 90%, of the length H of the blade 30 makes projection beyond the upper surface 46 of the shell 40.

[0063] There must be fixing means to hold the shell 40 on the rim 20 or on an associated element in the stator case.

Preferably, and as illustrated in Figure 3, the shell 40 comprises a first fixing element 51 to cooperate with the rim 20 so as to hold the shell 40 radially relative to the rim 20. It extends in particular from the first lateral side 47 to the second lateral side 48 of the shell 40 so as to improve cooperation with the rim 20.

[0064] The first fixing element 51 is here a tongue 51, even if other shapes are possible. This tongue 51 is in particular L-shaped extending from the upstream side 43. The tongue 51 comprises a first part 53 linked to the upstream side 43 and extending inwards, substantially perpendicular to the lower side 45, c that is to say substantially perpendicular to axis A. The tongue 51 also comprises a second part 54 extending the first part 53 substantially parallel to the interior side 45, that is to say substantially perpendicular to the first part 53. The tongue 51 thus forms a hook to cooperate with the rim 20.

[0065] As illustrated in Figure 3, the exterior surface 21 of the rim 20 is located on an exterior side of the rim 20. The latter also includes an upstream side 23, a downstream side 24 and a lower side 25. It includes a base 22 which extends inward from the interior side 25.

[0066] The rim 20 preferably comprises a second fixing element 26 to cooperate with the shell 40 and in particular with the first fixing element 51 so as to hold the shell 40 radially relative to the rim 20. The second fixing element fixing 26 is located here at the upstream side 23 of the rim 20. It is in particular a groove 26, in particular machined in the rim 20. The groove 26 extends for example continuously all along the the rim 20 so as to form a continuous circular groove. The shells 40 can thus be inserted around the blades 30 without taking into account their circular positioning with respect to the rim 20. Thus, the blades 30 can also be positioned on the rim 20 independently of their circular position.

[0067] When inserting the shell 40 around a blade 30, the tongue 51 of the shell 40 engages in the groove 26 of the rim 20 so as to hold the shell 40 radially relative to the rim 20.

[0068] It can also be noted that the first fixing element 51 is configured, in particular via the first part 53 of the tongue 51, to axially hold the shell 40 on the bladed disc 10, in particular on the rim 20. , and advantageously according to the direction of flow of the fluid.

[0069] | The rotating assembly of the invention may comprise, as illustrated in Figure 3, a ring 80 in particular centered on the axis A. The ring 80 is for example made of composite material, in particular with short fiber and in particular identical to the material constituting the peripheral portion 92 of the shell 40. The ring 80 is here U-shaped in a section in a plane comprising the axis A so that it comprises a lower side 81, a downstream side 82 and a upper side 83. This ring 80 comprises a third and a fourth fixing elements 84, 85.

[0070] The third fixing element 84 is configured to hold the panel radially relative to the rim 20. It is located here on the lower side 81 of the ring 80 and is in particular in the form of a first tab of ring 84 extending in particular substantially parallel to the lower side 25 of the rim 20.

[0071] The fourth fixing element 85 is configured to hold the shell 40 radially relative to the rim 20. The fourth fixing element 85 is located here on the upper side 83 of the ring 80 and is presented in particular under the shape of a second ring tongue 85 extending in particular substantially parallel to the upper side 45 of the shell 40, that is to say substantially parallel to said second ring tongue 85.

[0072] In this embodiment, the rim 20 preferably comprises a fifth fixing element 28 configured to cooperate with the third fixing element 84 of the ring 80. This fifth fixing element 28 is located here on the downstream side 24 of the rim 20 and is in particular a second groove 28. The second groove 28 can be identical to the first groove 26. It is in particular machined in the rim 20.

[0073] The second groove 28 is configured to receive the first ring tongue 84. Thus, when the ring 80 is inserted onto the bladed disc 10, the first ring tongue 84 engages in the second groove 28 of the rim 20 so as to hold the ring 80 radially relative to the rim 20. During this same insertion, the second ring tongue 85 will radially secure the shell 40 on the rim 20 by overlapping a part of the shell 40 located here on the upstream side 44 of the shell 40.

[0074] Variants of cooperation between the ring 80 and the shell 40 are illustrated in Figures 4a, 4b and 4c. In the embodiments of the invention illustrated in these figures, the shell 40 comprises a sixth fixing element 55 located here on the downstream side 44 of the shell 40. It extends in particular from the first lateral side to the second side side of the shell 40 so as to improve cooperation with the ring 40.

[0075] In Figure 4a, the sixth fixing element 55 is a second tongue 56. This second tongue 56 extends at the level of the downstream side 44 of the shell 40 in particular substantially parallel to the upper side 46. The second tongue of ring 85 is configured to cover this second tongue 56 so as to hold the shell 40 radially relative to the rim 20.

[0076] In Figure 4c, the shell 40 comprises a seventh fixing element 58, here a groove 58, located in particular on the downstream side 44 of the shell 40. The groove 58 is for example made in the second tongue 56.

[0077] In this embodiment, the ring 80 further comprises an eighth fixing element 86, in particular a tooth 86 preferably extending from the first lateral side to the second lateral side of the shell. The groove 58 is thus configured to receive the tooth 86 so as to maintain the shell 40 axially relative to the rim 20, in particular in both directions of the axial direction and in particular in a direction opposite to the direction 70 of the flow fluid in the tubomachine. Advantageously, the shell 40 and/or the ring 80 is made of a sufficiently flexible material to allow the insertion of the tooth 86 in the groove 58, preferably the shell 40 and/or the ring 80 is made of a composite material.

[0078] Figure 4b represents a variant embodiment of the invention in which the sixth fixing element 55 is a third groove 57 similar to the first and second grooves 26, 28. It is for example machined in the shell 40 When assembling the shell 40 on the bladed disc 10, the second ring tongue 85 is inserted into the third groove 57 so as to hold the shell 40 radially relative to the rim 20. The seventh fixing element 58 can be located in the third groove 57.

Advantageously, the rotating assembly 100 comprises at least one secondary damper 96 mechanically coupled to the peripheral portion 92 of the shell 40 to damp vibrations of the blade 30.

The secondary shock absorber 96 is for example made of elastomer or a vibrating sheet metal.

[0080] Preferably, the secondary damper 96 is arranged at a distance from the blade 30. The secondary damper 96 makes it possible to further dampen the vibrations of the blade 30.

[0081] According to examples illustrated in Figures 4b and 4c,

The secondary shock absorber 96 is fixed on the ring 80. The secondary shock absorber 96 and the peripheral portion 92 of the shell 40 are therefore mechanically coupled via the ring 80. Alternatively, the secondary shock absorber 96 is directly fixed on the peripheral portion 92 of the shell 40.

[0082] The mechanical coupling between the secondary shock absorber 96 and the peripheral portion 92 of the shell 40 can be carried out by bolting. According to this embodiment, the peripheral portion 92 of the shell 40 is preferably made of metal to facilitate the fixing of the secondary shock absorber 96 by a bolt.

[0083] Methods for manufacturing a shell 40 according to the invention are now described. Other processes are nevertheless possible.

[0084] First, the peripheral portion 92 of the shell 40 is manufactured. The peripheral portion 92 has a receiving space 98 intended to receive the central portion 90. Then, the central portion 90 is manufactured in the receiving space 98. According to preferred embodiments, the peripheral portion 92 is manufactured by molding or 3D printing.

[0085] According to another embodiment, the central portion 90 is manufactured before the peripheral portion 92.

[0086] In each case, the central portion 90 is secured to the peripheral portion 92. The connection is achieved for example via inserts made of composite material in the central portion 90 and/or via glue. Alternatively, the connection between the central portion 90 and the peripheral portion 92 is achieved by a slide and notch system.

[0087] In other words, the invention relates to a shell configured to be mounted on a blade support element of a turbomachine and capable of defining a profile of a vein for a flow of fluid through of the turbomachine, the shell comprising: - a central portion comprising a recess to allow the placement of the shell around a blade, and

- a peripheral portion at least partially surrounding the central portion, the central portion comprising an elastomeric material to damp vibrations of the blade.

[0088] The present invention has been described in relation to specific embodiments, which have purely illustrative value and should not be considered limiting. Generally speaking, the present invention is not limited to the examples illustrated and/or described above. The use of the verbs “understand”, “include”, “include”, or any other variant, as well as their conjugations, cannot in any way exclude the presence of elements other than those mentioned. The use of the indefinite article "UN", "une", or the definite article "le", "la" or "l'", to introduce an element does not exclude the presence of a plurality of these elements. The reference numbers in the claims do not limit their scope.

Claims (16)

Claims 1. Shell (40) configured to be mounted on a blade support element of a turbomachine and capable of defining a profile of a vein for a flow of fluid through the turbomachine, the shell (40) comprising: - a central portion (90) comprising a recess (41) to allow the placement of the shell (40) around a blade (30), and - a peripheral portion (92) at least partially surrounding the central portion (90) , characterized in that the central portion (90) comprises an elastomeric material to damp vibrations of the blade (30). 2. Shell (40) according to claim 1, where the peripheral portion (92) is made of metal or composite material. 3. Shell (40) according to any one of the preceding claims, where the elastomeric material of the central portion (90) is of the silicone or rubber type. 4. Shell (40) according to any one of the preceding claims, where the recess (41) comprises a bottom (42) to come into abutting contact with the blade (30). 5. Assembly for a turbomachine, comprising: - a shell (40) according to any one of the preceding claims; - a blade (30) inserted in the recess (41) of the central portion (90) of the shell (40) and in contact with the central portion (90), the blade (30) having a total length H. 6. Assembly according to the preceding claim, in which the central portion (90) has a thickness (E) greater than or equal to 7% of the total length H of the blade (30), preferably greater than or equal to 9%. 7. Rotating assembly (100) of a turbomachine, comprising: - an assembly according to claim 5 or 6; - a bladed disc (10) extending around an axis (A) and comprising a rim (20) having a rim surface (21) extending around the axis (A), the shell (40) assembly being attached to the bladed disc (10), the blade (30) of the assembly comprising a foot (31) fixed to the rim (20) and extending radially from the rim surface (21) . 8. Rotary assembly (100) according to the preceding claim, in which the shell (40) comprises a first fixing element (51) configured to cooperate with the rim (20) so as to radially hold the shell (40) relative to the rim (20). 9. Rotating assembly (100) according to the preceding claim, wherein the first fixing element (51) is configured to axially hold the shell (40) relative to the bladed disk (10). 10. Rotary assembly (100) according to claim 8 or 9, wherein the rim (20) comprises a second fixing element (26) configured to cooperate with the first fixing element (51) so as to radially hold the shell ( 40) relative to the rim (20). 11. Rotary assembly (100) according to any one of claims 7 to 10, further comprising a ring (80) comprising a third fixing element (84) and a fourth fixing element (85), the third fixing element (84) being configured to hold the ring (80) radially relative to the rim (20), the fourth fixing element (85) being configured to hold the shell (40) radially relative to the rim (20). 12. Rotary assembly (100) according to any one of claims 7 to 11, comprising at least two shells (40), each of them comprising a first side edge (49) and a second side edge (50) both extending substantially axially, the first side edge (49) of a first shell (40) being intended to overlap the second side edge (50) of an adjacent second shell (40). 13. Rotary assembly (100) according to any one of claims 7 to 12, comprising at least one secondary damper (96) mechanically coupled to the peripheral portion (92) of the shell (40) to damp vibrations of the blade (30). 14. Turbomachine compressor, comprising a rotor comprising a rotating assembly (100) according to any one of claims 7 to 13. 15. Method of manufacturing a shell (40) according to any one of claims 1 to 4, comprising the following steps: - manufacturing the peripheral portion (92) by molding, the peripheral portion (92) having a space of reception (98), - arrangement of the central portion (90) in the reception space (98), - joining of the central portion (90) to the peripheral portion (92). 16. Manufacturing method according to the preceding claim, in which the joining step is ensured via composite material inserts in the central portion (90) and/or via glue.