FR3114348A1 - Turbomachine turbine with CMC distributor with force take-up - Google Patents

Abstract

Turbomachine turbine with CMC distributor with force take-up Turbine comprising a casing and a distributor comprising an outer metal shroud (9) secured to the casing, an internal metal shroud, and a plurality of CMC distributor sectors (20) forming a crown extending between the outer shroud (9) and the inner shroud, each sector comprising a mast (6), an inner platform, an outer platform and at least one blade having a hollow profile through which the mast (6) passes. For each blade, the turbine comprises a retaining plate (10) comprising an upstream end (101) and a downstream end (102) in the axial direction (DA), and the outer metal shroud (9) comprises at least one radial abutment (103) extending in axial projection from said downstream end (95) towards the upstream end (94), the downstream end (102) of the retaining plate (10) being held radially between said radial stop (103) and a radially outer face (92) of the outer metal shroud (9), and the retaining plate (10) resting on a radially outer end of the mast (6). Figure for abstract: Fig. 2.

Description

Turbomachine turbine with CMC distributor with force take-up

The invention relates to turbomachines, in particular aeronautical turbine engines or industrial turbines comprising a turbine nozzle made of composite material with a ceramic matrix or with a matrix at least partially in ceramic, hereinafter referred to as CMC material.

The field of application of the invention is in particular that of aeronautical gas turbine engines. The invention is however applicable to other turbomachines, for example industrial turbines.

Improving the performance of turbomachines and reducing their polluting emissions leads to considering increasingly high operating temperatures.

For elements of hot parts of turbomachines, it has therefore been proposed to use composite materials with a ceramic matrix denoted CMC hereafter.

CMC materials are typically formed of a fibrous reinforcement made of refractory fibers, such as carbon or ceramic fibers, densified by a ceramic or at least partially ceramic matrix.

These materials have remarkable thermo-structural properties, that is to say mechanical properties which make them suitable for constituting structural elements and the ability to retain these properties at high temperatures. In addition, CMC materials have a much lower density than that of the metallic materials traditionally used for elements of hot parts of turbomachines.

Thus, documents WO 2010/061140, WO 2010/116066 and WO 2011/080443 describe the production of impeller blades of CMC turbomachines with integrated platform and heel. The use of CMC materials for turbine distributors has also been proposed, in particular in documents WO 2010/146288, FR 2 979 662 and EP 2 443 318.

A traditional metallic turbine nozzle has a crown shape composed of several joined sectors, each sector comprising an inner platform, an outer platform and a plurality of blades extending between and attached to the inner and outer platforms. The juxtaposed inner platforms form an inner shroud and the juxtaposed outer platforms form an outer shroud. The inner and outer shrouds delimit the gas flow path in the distributor.

Introducing a distributor, for example a high pressure distributor, in CMC makes it possible to increase the maximum tolerated temperature compared to a metal distributor, and thus to reduce the quantity of cooling air used. This thus makes it possible to increase the performance of the turbomachine.

However, CMC, due to its different properties from metal, is more sensitive to certain mechanical stresses. Indeed, the CMC has greater rigidity and less expansion. It behaves better in compression, but its allowable tensile stresses are lower than those of metal.

Moreover, the integration in a metallic environment of a CMC part is tricky because of the differential thermal expansions between the CMC and the metal. This is all the more delicate in a turbomachine, and more particularly in a high-pressure part of the turbomachine, because the environment is hot, which exacerbates the differences in thermal expansion coefficients between the materials, the aerodynamic forces undergone by a high pressure distributor being further elevated in this turbine area.

Distributors made of CMC are known, such as for example a turbine distributor comprising an external supporting shroud integral with a casing, an internal supporting shroud, and a plurality of sectors of CMC distributors forming a ring extending between the shroud outer support and the inner support shell. Each distributor sector rests on the inner and outer support shells and comprises an inner platform, an outer platform, and at least one blade extending between the outer platform and the inner platform and fixed thereto.

However, there is a need to improve the known solutions with regard to the deterministic maintenance of the distributor sector in CMC with the inner shroud, in particular in terms of axial maintenance of the distributor sector and in terms of taking up aerodynamic forces.

Furthermore, a significant pressure differential is exerted on the casing under the distributor in the radial and axial directions. This casing is used to create a seal between the rotor and the stator. This pressure difference is the source of a force which, if it were exerted on the CMC, would be high given the allowable values of the material.

It is also known, in particular from document FR 3 061 928 and FR 2 973 435, a distributor as described above and further comprising a reinforcing mast extending radially inside the blades between the two platforms allowing the distributor to be held to the housing by the mast.

However, such a solution takes up both, via the mast, the forces relating to the pressure differential under the distributor and the aerodynamic forces on the CMC crown. In addition, for the reasons mentioned above relating to the different mechanical behavior between CMC and metallic material, it is difficult to position the CMC part on the metallic environment by clamping it.

During turbine operation, a large radial clearance is generated between the mast and the blade it passes through. More specifically, the expansion of the mast being greater than the expansion of the CMC blade, a radial play greater than 0.5 mm, or even greater than 1 mm, may appear between the mast and the blade through which it passes. This radial play generates an uncertainty on the position of the blade, the aerodynamic plating becoming random up or down according to the radial resultant of the aerodynamic force.

There is therefore a need to improve the deterministic maintenance of the distributor in CMC of this solution.

The invention aims to overcome the disadvantages mentioned above and to overcome the difficulties mentioned above by proposing a turbomachine turbine comprising a turbine distributor at least partly made of CMC, the assembly of which is simplified and adapted to maintain its sectors distributor in a deterministic way while allowing the sectors to deform independently of the metal parts at the interface, and guaranteeing satisfactory sealing.

More particularly, the invention aims to limit, or even eliminate, the radial clearance opening up in operation between the mast and the CMC blade.

An object of the invention proposes a turbomachine turbine comprising a casing, an outer metal support shroud integral with the casing, an inner metal support shroud, and an annular turbine distributor defining an axial direction and a radial direction and comprising a plurality of distributor sectors made of composite material with a ceramic matrix forming a crown extending between the outer support shroud and the inner support shroud.

Furthermore, each sector comprises a metal mast, an inner platform, an outer platform and at least one blade extending radially between the inner and outer platforms and having a hollow profile defining a radially extending inner housing. The inner and outer platforms of each sector each have an orifice communicating with said internal housing of the blade. The outer metal shroud comprises an upstream end and a downstream end in the axial direction, and an orifice for each mast. Each mast passes through an orifice of the outer metal shroud then said orifices of the outer and inner platforms and the internal housing. The mast of each blade is fixed to said casing on the one hand and is linked to said sector on the other hand.

According to a general characteristic of the invention, for each blade, the turbine comprises a retaining plate comprising an upstream end and a downstream end in the axial direction, and the outer metal shroud comprises at least one radial stop extending axially from said downstream end towards the upstream end, the downstream end of the retaining plate being held radially between said radial abutment and a radially outer face of the outer metal shroud, and the retaining plate resting on a radially outer end of the mast.

The connection made by the invention between the mast and the outer support shell already makes it possible to greatly increase the tightness between the vein defined by the annular CMC distributor and the zone radially outside of this vein and thus to improve the performance of the turbine, which makes it possible to eliminate many interface zones.

The retaining plate as defined in the invention makes it possible to secure the metal mast to the outer shroud using an intermediate part stiffening the assembly, in particular between the upstream and the downstream, and making it possible to guarantee the maintenance in the radial position of the metal mast on the outer shroud at all operating points without modifying the axial assembly of the turbine.

According to a first aspect of the turbine, the outer support shroud may comprise a shoulder extending in the radial direction at the downstream end of the outer shroud over the entire circumference of the outer support shroud, each radial abutment extending from the shoulder towards the upstream end of the outer metal shroud.

The shoulder makes it possible to form an elevation from which the abutment can extend to form, with the radially outer surface of the metal shroud, a housing making it possible to receive a downstream end of the retaining plate.

According to a second aspect of the turbine, the mast may comprise at least one hooking projection on the outer support shroud arranged between the radially outer face of the metal shroud and the retaining plate, said at least one hooking projection having at least one portion extending from the radially outer end of the mast in a direction opposite the center of the mast and in a plane orthogonal to the radial direction.

The hooking projection extending in a plane orthogonal to the radial direction makes it possible to form a bearing surface arranged between the outer surface of the metal shroud and the retaining plate. This arrangement of the protrusion ensures a greater radial support of the mast compared to the metal shell.

Preferably, said at least one hooking projection of the mast comprises a single portion extending over the entire circumference of the mast from a radially outer end of the mast.

According to a third aspect of the turbine, said at least one hooking projection of the mast of each blade can extend in a plane, and the radially outer face of the outer support shroud can comprise a facet for receiving a projection attachment for each blade, each facet being planar, that is to say extending in a plane defined by only two non-circular directions.

The facets made for each of the blades make it possible to present a plane/plane contact between the mast and the shell, thus improving the sealing between the two elements facilitating the positioning of the mast. The ferrule is machined so as to present as many "facets" as blades and therefore as masts.

According to a fourth aspect of the turbine, for each mast, the external support shroud may further comprise a centering pin extending in radial projection from said radially external face on a portion downstream of the mast, the attachment projection of each mast comprises a centering orifice configured to cooperate with an associated centering pin, and the retaining plate may comprise a centering orifice intended to be coaxial with the centering orifice of the hooking projection and configured to cooperate with a associated centering pin.

The centering pin on the external support shroud and the centering orifice provided on the mast, for example on a centering projection extending from the external radial end of the mast or directly on one or the attachment projection, provides a first point of anti-rotation.

According to a fifth aspect of the turbine, for each mast, the external support shroud comprises screws and threaded holes arranged on a portion of the external metal shroud upstream of the mast and each configured to cooperate with an associated screw, the projection d attachment comprises first holes for passing screws and the retaining plate comprises second holes for screws, the screw holes each being intended to be coaxial with a tapped hole, each screw successively passing through a hole for passing screws in the plate retainer, a screw hole for the hooking projection and a threaded hole.

According to a sixth embodiment of the turbine, the external support shroud can be made in a single piece, that is to say be non-sectored. This makes it possible to mount the mast radially from the outside of the external support shell and to limit as much as possible the leaks which would be present in the case of a sectorized shell.

According to a seventh embodiment of the turbine, the mast can be hollow.

The mast thus makes it possible to bring air into the cavity radially inside the internal shroud in order to pressurize it and thus prevent the air circulating in the vein extending between the internal and external platforms of the sectors of distributor is reintroduced out of this vein and thus reduces the performance and increases the risk of overheating of the parts.

According to an eighth embodiment of the turbine, the outer support shroud may comprise an upstream end and a downstream end in the axial direction, and a shoulder extending in the radial direction from one of the upstream or downstream ends of the outer shroud over the entire circumference of the outer support shroud, and the mast of each blade may include a support for anti-rotation of the mast relative to the outer support shroud projecting in the axial direction from the radially outer end of the mast until it comes to bear in the axial direction against the shoulder of the outer support shell.

The support of the mast on the shoulder of the external support ring keeps the mast and thus the blade from any rotation around a radial axis.

The invention also relates to a turbomachine comprising a turbomachine turbine as defined above.

The invention also relates to an aircraft comprising at least one turbomachine as defined above.

Figure 1 is a schematic sectional view of a sector of a turbine according to one embodiment of the invention.

Figure 2 is a schematic assembled view of an outer support shroud and a mast of the turbine of Figure 1.

Figure 3 shows an exploded schematic view of an outer support shroud and a mast of the turbine of Figure 1.

In Figure 1 is shown a schematic sectional view of a sector of a turbine according to one embodiment of the invention. To clarify this first figure, figure 1 does not include the retaining plate 10.

A high-pressure turbine 1 of a turbomachine, for example an aeronautical turbine engine, as partially shown in FIG. 1, comprises a plurality of fixed distributors 2 which alternate with moving wheels in the direction of flow of the gas flow F, indicated by an arrow in Figure 1, in the turbine 1 and which are mounted in a turbine housing.

Each impeller includes a plurality of vanes having an inner shroud, and at least one blade extending from and bonded to the inner shroud. On the inner side of the inner shroud, the blade is extended by a foot engaged in a housing of a disc. On the outer side, the tip of the blades faces an abradable material carried by a ring to seal the tips of the blades.

Throughout the present text, the terms "inner" or "internal" and "outer" or "external" are used in reference to the position or the orientation with respect to the axis of rotation of the turbine 1 which defines the direction axial D _A of turbine 1.

The blades of the moving wheel can be traditional metal blades or blades made of CMC material obtained for example as described in the documents WO 2010/061140, WO 2010/116066, WO 2011/080443.

At least one of the distributors 2 of the turbine 1 is formed by joining together several sectors of annular distributors 20 made of CMC material to form a complete ring. The arrow D _A indicates the axial direction of the distributor 2 while the arrow D _R indicates the radial direction of the distributor 2 and the mark D _C indicates the circumferential direction.

Each dispenser sector 20 of dispenser 2 comprises an inner platform 24, an outer platform 26 and a blade 28 extending between and attached to the inner and outer platforms 24 and 26. Alternatively, several blades could extend between the inner and outer platforms of the same distributor sector. Once assembled with the casing of the turbine 1, the sectors 20 form a single crown of distributors 2 having an inner shroud formed by the juxtaposition of the inner platforms 24 of the sectors 20 and an outer shroud formed by the juxtaposition of the outer platforms 26 of the sectors 20.

The inner shroud and the outer shroud form between them a fluid flow vein 45 inside which the gas flow F flows during the operation of the turbine 1.

Throughout the text, the terms “upstream” and “downstream” are used in reference to the direction of flow of the gas flow F in the stream 45 indicated by an arrow.

The inner platforms 24 each have an outer surface 24e intended to be in contact with the gas flow F, and therefore arranged radially opposite the outer platforms 26 forming the outer shroud. The interior platforms 24 also have an interior surface 24i arranged facing the axis of rotation of the turbine 1.

The outer platforms 26 each have an outer surface 26e arranged facing the casing and formed by the surface of the second portion 262 of the outer platforms 26 oriented radially outwards. The outer platforms 26 also have an inner surface 26i intended to be in contact with the gas flow F, and therefore arranged radially facing the inner platforms 24 forming the inner shroud and facing the axis of rotation of the turbine 1.

The distributor 2 is held between an inner metal shroud 5 and an outer metal shroud 9 between which extends the crown formed by the assembly of the ring sectors 20 of the distributor 2. The outer metal shroud 9 is integral with the casing and has an inner surface 91 and an outer surface 92 in the radial direction D _R .

As illustrated in Figure 1, each blade 28 has a hollow profile having an inner housing 280 extending over the entire height of the blade 28, that is to say between the inner platform 24 and the outer platform 26 of the ring sector 20. The inner platform 24 of each distributor sector 20 comprises an orifice 245 whose shape corresponds to the section of the inner housing 280 in the plane in which the inner platform 24 extends. 26 of each distributor sector 20 comprises an orifice 265 whose shape corresponds to the section of the interior housing 280 in the plane in which the interior platform 26 extends. The orifices 245 and 265 of the interior 24 and exterior 26 platforms are made in the extension of the interior housing 280 of the blade 28.

The inner housing 280 of the blade 28 and the orifices 245 and 265 of the inner 24 and outer 26 platforms can be connected to a cooling system delivering a flow of cooling air from the housing into the blade 28 and the inner platforms 24 and exterior 26.

As illustrated in Figures 2 and 3 which show two schematic views of an outer support shroud 9, a mast 6, and a retaining plate 10 of the turbine 1 of the figure, the turbine 1 comprises in addition, for each distributor sector 20, a mast 6 extending in the radial direction D _R . In Figure 2, the outer metal shroud 9, the retaining sheet 10 and the mast 6 are assembled, and in Figure 3, the outer metal shroud 9, the retaining sheet 10 and the mast 6 are exploded.

As illustrated, the mast 6 comprises a mast head 61 resting on the outer surface 92 of the outer metal shroud 9, and a rod 62 projecting from the head 61 in the radial direction D _R towards the inside and configured to pass through the outer metal shroud 9, the inner housing 280 of the blade 28 and the orifices 245 and 265 of the inner 24 and outer 26 platforms being aligned with the inner housing 280 of the blade 28.

In other words, the mast 6 comprises a radially internal first end 6i and a radially external second end 6th, a body 62 extending substantially in the radial direction D _R between the first and second ends 6i and 6th of the mast 6, and a masthead 61 projecting in a plane orthogonal to the radial direction D _R from the second 6th end of the mast 6. The masthead 61 forms a flat support extending in a plane orthogonal to the radial direction D _R.

The mast 6 is hollow to bring air into the cavity radially inside the internal shroud in order to pressurize it and thus prevent the air circulating in the vein extending between the internal and external platforms of the distributor sectors is reintroduced outside this vein and thus reduces the performance and increases the risk of overheating of the parts. The mast 6 thus comprises an internal housing 60 extending in the radial direction D _R between the first and second ends 6i and 6e of the mast 6.

The outer metal shroud 9 comprises orifices 90 for receiving the mast 6 shaped to be traversed by a mast 6, and flat facets 93 to each receive a mast head 61 in support.

The outer metal shroud 9 comprises an upstream end 94 and a downstream end 95 in the axial direction D _A . On its downstream end 95, the outer metal shroud 9 comprises a shoulder 96 extending in the radial direction D _R over the entire circumference of the outer metal shroud 9. The outer metal shroud 9 further comprises, for each blade 28, and therefore for each mast 6, a centering pin 97 fitting into an orifice 98 provided in the outer metal shroud 9. When the centering pin 97 is inserted into the orifice 98, the pin 97 protrudes into the radial direction D _R from the radially outer face 92 of the outer metal shroud 9. The centering pins 97 are arranged, in this embodiment, on a downstream portion of the outer metal shroud 9, that is to say at near the downstream end 95 of the outer metal shroud 9, between the shoulder 96 and the upstream end 94.

The downstream end 95 of the outer metal shroud 9 also forms a hook open downstream for fixing the outer metal shroud 9 to the casing.

The masthead 61 comprises an anti-rotation support 64 extending in the circumferential direction D _C coming to bear in the axial direction D _A against the shoulder 96 of the downstream end 95 of the outer metal shroud 9 to maintain the mast 6 and thus the blade 28 with which the mast 6 cooperates from any rotation around a radial axis. Each mast 6 further comprises a centering orifice 65 shaped to cooperate with one of the centering pins 97 of the outer metal shroud 9.

In addition, in the illustrated embodiment, the flat support formed by the mast head 61 is arranged in the radial direction D _R between the outer surface 92 of the metal shroud 9 and the retaining plate 10.

The retaining plate 10 has an upstream end 101 and a downstream end 102 in the axial direction D _R . And the outer metal shroud 9 comprises a radial abutment 103 projecting in the axial direction D _A from the shoulder 96 of the downstream end 95 towards the upstream end 94. The downstream end 102 of the retaining plate 10 has a thickness in the radial direction D _R less than the distance in the radial direction D _R extending between the outer surface 92 of the metal shroud 9 and the radial stop 103. The downstream end 102 of the retaining plate 10 is held radially between the radial stop 103 and the outer surface 92 of the outer metal shroud 9.

In the illustrated embodiment, the outer metal shroud 9 further comprises, for each mast 6, threaded holes 99 on an upstream portion and each mast 6 comprises, in the mast head 61, upstream fixing holes 66 configured to overlap the threaded holes 99 of the outer metal shroud 9 when the mast 6 is mounted on the outer metal shroud 9.

The retaining plate 10 further comprises three orifices: a centering orifice 104 and two upstream retaining orifices 105. The centering orifice 104 of the retaining plate 10 located on a downstream portion of the retaining plate 10 and intended to receive the centering pin 97. The centering orifice 104 of the retaining plate 10 is coaxial with the centering orifice 65 of the mast 6 and with the centering orifice 98 of the outer metal shroud 9. The two orifices of upstream support 105 are located on an upstream portion of the support plate 10 and coaxial with the mounting holes 66 of the mast and the corresponding threaded holes 99 of the outer metal shroud 9.

The outer metal shroud 9 comprises screws 990 each passing through a retaining hole 105 of the retaining plate 10, an upstream fixing hole 66 of the mast 6 and a threaded hole 99 of the retaining shroud, to fix the mast 6 to the outer metal shroud 9. The retaining plate 10 makes it possible, using the screws 990 and the radial stop 103, to hold the mast 6 in the radial position.

The retaining plate 10 further comprises a main orifice 106 opposite the orifice of the internal housing 60 mast 6 to allow the passage of the cooling flow.

To maintain the blade 28 in position, the mast 6 further comprises two projecting portions 63 extending in a plane transverse to the radial direction D _R . In the embodiment illustrated in FIGS. 1 to 3, a first projecting portion 63 forms a first support at a first radial position and a second projecting portion 63 forms a second support at a second radial position. The first radial position is located radially inside the second radial position, that is to say between the center of revolution of the turbine 1 and the second radial position.

The first and the second supports form two lugs extending substantially along the axial direction D _A on a portion of the mast 6 intended to be in the interior housing 280 of the blade 28. The two projecting portions 63 of the mast 6 each form a protrusion of which at least a part is in contact with the blade 28 to hold the blade 28 in position.

In addition, the internal support shroud 5 comprises orifices configured to receive the masts 6. The mast 6 makes it possible to provide a means of fixing the sector 20 of the CMC distributor from above, that is to say to the casing, while minimizing the bending moment, insofar as the bending length is reduced by about half by the mast 6 crossing the distributor sector. Each distributor sector 20 is thus maintained in a deterministic manner, that is to say in such a way as to prevent the distributor sector 20 from vibrating and by controlling its position, and this while allowing the distributor sector 20 to deform under the effects of temperature and pressure, among other things, independently of the metal parts at the interface.

In the case where each distributor sector comprised several blades, the turbine would comprise, at most, a corresponding number of masts for each distributor sector.

In a variant, the masthead 61 may comprise a plurality of projections extending from the second 6th end of the mast 6, some of them comprising at least one of the elements for maintaining or centering the mast 6.

The turbomachine turbine according to the invention comprises a turbine distributor at least partly made of CMC, the assembly of which is simplified and adapted to maintain its distributor sectors in a deterministic manner while allowing the sectors to deform independently of the metal parts at the interface, and improving the seal between the mast and the outer metal shroud.

Claims (10)

Turbine (1) of a turbomachine comprising a casing, an outer support shroud (9) made of metal secured to the casing, an inner support shroud (5) made of metal, and an annular turbine distributor (2) defining an axial direction (D _A ) and a radial direction (D _R ) and comprising a plurality of distributor sectors (20) made of composite material with a ceramic matrix forming a crown extending between the outer support shroud (9) and the inner support shroud (5 ),
each sector (20) comprising a metal mast (6), an inner platform (24), an outer platform (26) and at least one blade (28) extending radially between the inner and outer platforms (24, 26) and having a hollow profile defining an internal housing (280) extending radially, the inner and outer platforms (24, 26) each having an orifice (245, 265) communicating with said internal housing (280) of the blade (28), the outer metal shroud (9) comprising an upstream end (94) and a downstream end (95) in the axial direction (D _A ), and an orifice (90) for each mast (6), and the mast (6) passing through an orifice (90) of the outer metal shroud (9), said orifices (245, 265) of the platform (24, 26) and the internal housing (280) and being fixed to said casing on the one hand and in connection with said sector (20) on the other hand,
characterized in that , for each blade (28), the turbine (1) comprises a retaining plate (10) having an upstream end (101) and a downstream end (102) in the axial direction (D _A ), and the outer metal shroud (9) comprises at least one radial abutment (103) extending in axial projection from said downstream end (95) towards the upstream end (94), the downstream end (102) of the retainer (10) being held radially between said radial abutment (103) and a radially outer face (92) of the outer metal shroud (9), and the retaining plate (10) being arranged on a radially outer end of the mast (6 ). Turbine (1) according to claim 1, in which the outer support shroud (9) comprises a shoulder (96) extending in the radial direction (D _R ) at the downstream end (95) of the outer shroud (9 ) over the entire circumference of the outer support shroud (9), each radial abutment (103) extending from the shoulder (96) in the direction of the upstream end (94) of the outer metal shroud (9). Turbine (1) according to one of Claims 1 or 2, in which the mast (6) comprises at least one attachment projection (61) to the external support shroud (9) placed between the radially external face (92) of the metal shroud (9) and the retaining plate (10), said at least one hooking projection (61) having at least one portion extending from the radially outer end (6e) of the mast (6) in a direction opposite the center of the mast (6) and in a plane orthogonal to the radial direction (D _R ). Turbine (1) according to Claim 3, in which the said at least one attachment projection (61) of the mast (6) of each blade (28) extends in a plane, and the radially outer face (92) of the outer support shroud (9) comprises a facet (93) for receiving a hooking projection (61) for each blade (28), each facet (93) being planar. Turbine (1) according to one of Claims 3 or 4, in which, for each mast (6), the external support shroud (9) further comprises a centering pin (97) extending in radial projection from the said radially outer face (92) on a downstream portion of the mast (6), the attachment projection (61) of each mast (6) comprises a centering orifice (65) configured to cooperate with a centering pin (97) associated, and the retaining plate (10) comprises a centering orifice intended to be coaxial with the centering orifice (65) of the attachment projection (61) and configured to cooperate with an associated centering pin (97) . Turbine (1) according to one of Claims 3 to 5, in which, for each mast (6), the external support shroud (9) comprises screws (990) and threaded holes (99) arranged on a portion of the outer metal shroud (9) upstream of the mast (6) and each configured to cooperate with an associated screw (990), the hooking projection (61) comprises first holes for passing screws and the retaining plate (10 ) comprises second screw holes, the screw holes each being intended to be coaxial with a threaded hole (99), each screw (990) successively passing through a screw passage hole of the retaining plate (10), a hole screw passage of the hooking projection (61) and a threaded hole (99). Turbine (1) according to one of Claims 1 to 6, in which the external support shroud (9) is in one piece. Turbine (1) according to any one of claims 1 to 7, in which the mast (6) is hollow. Turbomachine comprising a turbine (1) according to one of claims 1 to 8. Aircraft comprising at least one turbomachine according to claim 9.