FR3137415A1 - Sealing assembly for low pressure turbine stator and low pressure turbine ring comprising such a sealing assembly - Google Patents

Abstract

Sealing assembly for low pressure turbine stator and low pressure turbine ring comprising such a sealing assembly One aspect of the invention relates to a sealing assembly (100) for a low pressure turbine stator extending around a central axis (A), the sealing assembly (100) comprising a sealing sector (110) comprising: a base (111), a hook (113) extending from the base, an annular portion (112) extending radially projecting from an intersection of the base and the hook, said sealing assembly (100) further comprising an annular sector (120) extending radially from the annular portion (112) of the sealing sector (110) towards the central axis (A) and fixed to at least one end (114) of said sealing sector to form a thermal protection barrier. Another aspect of the invention relates to a low pressure turbine ring for a turbomachine, comprising a plurality of sealing assemblies (100) positioned circumferentially next to each other. Figure to be published with the abstract: Figure 5

Description

Sealing assembly for low pressure turbine stator and low pressure turbine ring comprising such a sealing assembly TECHNICAL FIELD OF THE INVENTION

The present invention relates to a sealing assembly for a low-pressure turbine stator, comprising an annular sector fixed on a sealing sector to form a thermal barrier intended to thermally protect the shell of the low-pressure distributor of stage 1 of the turbine. The invention also relates to a low-pressure turbine ring comprising such a sealing assembly.

The invention finds applications in the field of aeronautics and, in particular, in the field of low pressure turbines for turbomachines.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

In a turbomachine, the low pressure turbine (or LP turbine) comprises, as shown in the , a stator 1a and a rotor 1b. The rotor 1b comprises wheels 2 assembled axially to each other by annular flanges each comprising a disk 3 carrying individual blades 4. The stator 1a comprises annular rows of fixed blades 8, forming a distributor. These fixed blades 8, housed between the wheels 2 of the rotor 1b, are mounted, by their radially external ends, on the casing 5 of the LP turbine. Between each low-pressure distributor ring, positioned radially above the moving wheels 2, a ring of sealing sectors 6A ensures sealing above the moving blades.

The LP turbine also includes a ferrule 10, an example of which, in accordance with the prior art, is shown in the . The LP turbine shroud 10 is a circular part, of large diameter, whose role is to ensure the positioning and maintenance of the low pressure distributors stage 1 in a vein of said turbine. The shroud 10 is a part mounted at the interface of numerous components of the LP turbine and which must satisfy a large number of functions linked to these components. The shroud 10 is in particular mounted at the interface of the distributors 20 of the turbine.

One of the functions of the ferrule 10 is to allow the centering of the LP turbine on a high pressure (HP) turbine. The ferrule 10 satisfies very precise assembly constraints and meets the mechanical strength requirements.

Another function of the ferrule 10 is to ensure the axial stopping of the distributors 20.

Yet another function of the shroud 10 is to allow a flow of cold air to pass through in order to supply fresh air to the hooks 30 of the low-pressure turbine casing 40 which is in contact with the hooks 30' of a sealing sector 90. Indeed, during operation, two air flows 41, 51 pass around the shroud 10. A flow of cold air 41 coming from the inter-turbine casing 40' and a flow of hot air 51 coming from a vein 50. At the time of takeoff of the aircraft, the shroud 10 is in contact, on the one hand, with the flow of cold air 41 at a temperature of approximately 400° and, on the other hand, with the flow of hot air 51 at a temperature of approximately 900°. The temperature difference between these two air flows imposes a high thermal gradient on the shell 10. The thermal constraints are such that current materials cannot withstand this environment for long. Indeed, under the effect of the thermal gradient, the shell 10 tends to compress on itself, which leads to local plasticization of the material causing cracks to appear. These cracks are cracks that can propagate and eventually join together, which can then release a piece of the shell 10 into the vein 50.

Typically, in most LP turbines, the hot air flow and the cold air flow are physically separated by the foot 70 of the shell 10. The shell foot 70 is therefore one of the hottest areas of the LP turbine and is one of the locations most prone to crack formation. An example of a shell foot 70 exhibiting the beginning of a crack is shown in FIG. . In this example, the crack 80 is located at a leg 71 of the foot 70 of the shell 10 which is the hottest zone of the shell 10. The initiation of the crack 80 generally occurs at the rear of the shell 10, in an angular zone 72 of the foot 70, because this zone is in contact with the hot air flow 51 of the vein 50. The propagation of the crack 80 then generally occurs upstream of the shell 10, then goes back up towards the end 73 of the foot 70. Another example of a crack 85 is shown, from the front, on the .

One solution to this problem could be to protect the shell by the distributor by reversing the position of the shell and the distributor. However, this solution would be difficult to implement because it would require too many modifications to the LP turbine.

There is therefore a real need for a relatively simple solution to implement to improve the mechanical strength of the shell and limit the risk of cracking.

To address the above-mentioned problems of crack formation, the applicant proposes a sealing assembly in which an annular sector is mounted radially on the sealing sector in order to thermally protect the foot of the ferrule and, thus, to limit the risk of cracks appearing on said ferrule.

• une base,
• un crochet s’étendant depuis la base,
• une portion annulaire s’étendant radialement en saillie depuis une intersection de la base et du crochet ,

ledit ensemble d’étanchéité étant caractérisé en ce qu’il comporte en outre un secteur annulaire s’étendant radialement depuis la portion annulaire du secteur d’étanchéité vers l’axe central et fixé à au moins une extrémité dudit secteur d’étanchéité pour former une barrière de protection thermique.According to a first aspect, the invention relates to a sealing assembly for a low pressure turbine stator extending around a central axis, the sealing assembly comprising a sealing sector comprising:

• a base,
• a hook extending from the base,
• an annular portion extending radially projecting from an intersection of the base and the hook,

said sealing assembly being characterized in that it further comprises an annular sector extending radially from the annular portion of the sealing sector towards the central axis and fixed to at least one end of said sealing sector to form a thermal protection barrier.

This sealing assembly protects the base of the shell from the hot air flow, which reduces the thermal gradient of the shell and reduces the stresses induced on the part. In fact, the annular sector mounted in the extension of the sealing sector forms a thermal barrier that prevents the hot air flow from the vein from coming into contact with the base of the shell. Mounting the annular sector on the sealing sector has the additional advantage of not requiring any modification to the other parts of the turbine.

In this application, the terms “upstream” and “downstream” are defined relative to the direction of flow in the turbine, along the central axis of the turbine. The terms “internal” and “external” are defined radially relative to the axis of rotation, or central axis, of the shell, an internal (or inner) surface being radially closer to the axis of rotation than an external (or outer) surface.

• le secteur annulaire comporte une section en forme de T renversé
• le secteur annulaire est fixé sur le secteur d’étanchéité par une brasure double, en deux zones distinctes
• le secteur annulaire comporte une première zone de fixation localisée sur une surface externe d’une jambe de la forme en T et une deuxième zone de fixation localisée sur une surface aval d’un bras de la forme en T
• la portion annulaire du secteur d’étanchéité comporte une section en forme sensiblement de L avec une partie radiale et une partie axiale, la première zone de fixation étant en contact avec une surface interne de la partie axiale et la deuxième zone de fixation étant en contact avec une surface d’extrémité de la partie radiale
• le secteur annulaire comporte une forme arrondie de même courbure que le secteur d’étanchéité
• le secteur annulaire est réalisé par fabrication additive
• le secteur annulaire comporte au moins une cavité débouchant à une extrémité circonférentielle dudit secteur annulaire pour recevoir une plaquette d’étanchéité.

In addition to the characteristics which have just been mentioned in the preceding paragraph, the sealing assembly according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations:

• the annular sector has a section in the shape of an inverted T
• the annular sector is fixed to the sealing sector by a double brazing, in two separate zones
• the annular sector comprises a first fixing zone located on an external surface of a leg of the T-shape and a second fixing zone located on a downstream surface of an arm of the T-shape.
• the annular portion of the sealing sector comprises a substantially L-shaped section with a radial portion and an axial portion, the first fixing zone being in contact with an internal surface of the axial portion and the second fixing zone being in contact with an end surface of the radial portion
• the annular sector has a rounded shape with the same curvature as the sealing sector
• the annular sector is produced by additive manufacturing
• the annular sector comprises at least one cavity opening at a circumferential end of said annular sector to receive a sealing plate.

A second aspect of the invention relates to a low pressure turbine ring for a turbomachine, characterized in that it comprises a plurality of sealing assemblies as defined above and positioned circumferentially next to each other.

Advantageously, the low pressure turbine ring comprises, between two annular sectors, a sealing plate partially housed in the annular sectors.

• un anneau tel que défini ci-dessus, comportant une pluralité d’ensembles d’étanchéité, et
• une virole annulaire comportant un pied s’étendant radialement,
• chaque ensemble d’étanchéité de l’anneau étant positionné en vis-à-vis du pied de la virole pour former une barrière de protection thermique.

A third aspect of the invention relates to a system for a low pressure turbine of a turbomachine, characterized in that it comprises:

• a ring as defined above, comprising a plurality of sealing assemblies, and
• an annular ferrule having a radially extending foot,
• each sealing assembly of the ring being positioned opposite the foot of the ferrule to form a thermal protection barrier.

A fourth aspect of the invention relates to a turbomachine comprising at least one sealing assembly as defined above.

BRIEF DESCRIPTION OF THE FIGURES

Other advantages and characteristics of the invention will appear on reading the description which follows, illustrated by the figures in which:

There , already described, represents a partial schematic half-view in axial section of a low-pressure turbine of a turbomachine;

There , already described, represents a schematic view, in longitudinal section, of a part of a low pressure turbine comprising a sealing sector according to the state of the art;

There , already described, represents a schematic view, in longitudinal section, of a ferrule foot according to the state of the art;

There , already described, represents an example of a crack initiated in a shell foot according to the state of the art;

There represents a schematic view, in longitudinal section, of a part of an LP turbine equipped with a sealing assembly according to the invention;

There represents a perspective view, front and rear, of a sealing assembly for an LP turbine according to the invention;

There represents a schematic view, in longitudinal section, of the sealing assembly according to the invention, with the fixing zones; and

There represents a schematic front view of a portion of a ring comprising two sealing assemblies according to the invention, linked by a plate.

DETAILED DESCRIPTION

An exemplary embodiment of a sealing assembly comprising an annular sector mounted at the end of a sealing sector of an LP turbine according to the invention is described in detail below, with reference to the appended drawings. This example illustrates the characteristics and advantages of the invention. It is however recalled that the invention is not limited to this example.

In the figures, identical elements are identified by identical references. For reasons of readability of the figures, the size scales between elements represented are not respected.

An example of a sealing assembly 100 according to the invention is shown in the . There also shows the environment of this sealing assembly 100. It shows in particular the shell 10 of the LP turbine, in connection with the inter-turbine casing 40' (better known by its English designation TCF for "Turbine Center Frame") and with the low-pressure turbine casing 40, all three connected by a bolted connection 60. The shell 10 is an annular element mounted around the central axis A, shown schematically in the to symbolize the axis of rotation of the turbine. The ferrule 10 comprises a foot 70 having an L-shaped section, in contact with the distributors 20.

The sealing assembly 100 according to the invention is positioned downstream of the shell 10 and extends along the central axis A. The sealing assembly 100 comprises a sealing sector 110 and an annular sector 120 fixed to the sealing sector 110. The sealing sector 110 is similar to the sealing sectors of current LP turbines and incorporates a hook 113 in connection with the hook 30 of the casing 40 of the LP turbine to ensure the maintenance of said sealing sector 110 on the casing 40. Like most sealing sectors, the sealing sector 110 of the sealing assembly 100 comprises a base 111 located downstream of the hook 113 and an annular portion 112. The annular portion 112 extends radially in projection from an intersection between the base 111 and the hook 113. The annular portion 112 has an L-shaped section which comprises a radial portion 112a forming the leg of the L and extending generally radially from the base 111 towards the central axis A and an axial portion 112b forming the arm of the L and extending substantially axially from the radial portion 112a in the upstream direction.

The annular sector 120 is a part added to the end of the sealing sector 110. This part is tangentially rounded so as to match the curved shape, i.e. partially circular, of the sealing sector 110. Indeed, the sealing sector 110 being a sectorized part, its upstream face has a curvature whose radius is adapted so that, after assembly, all of the sealing sectors 100 form a ring. The annular sector 120 therefore has a rounded shape with the same curvature as the sealing sector.

The shape of the annular sector 120, as described below, is determined so that there is no contact between said annular sector and the shell 10 when the turbine is in operation.

The annular sector 120 is designed to protect the foot 70 of the ferrule 10. For this, the annular sector 120 extends downstream of the foot 70, substantially radially, in the extension of the sealing sector 110 and, in particular, in the extension of the axial part 112b of the annular portion 112. In other words, the annular sector 120 extends in a radial direction, towards the central axis A, from the upstream end 114 of the sealing sector 110. The annular sector 120 thus comprises an upstream surface 121a substantially parallel to the leg 71 of the ferrule foot 70. The annular sector 120 has a height at least equal to the height of the leg 71 of the ferrule foot 70, the height being considered in the radial direction. Thus positioned, the annular sector 120 forms a thermal protection barrier against the flow of hot air circulating in the vein 50. Indeed, the annular sector 120 is designed so as to extend as much as possible radially towards the central axis A in order to protect the shell foot 70 while preserving a clearance with the distributors 20 allowing the passage of the sealing sectors above the low-pressure distributors (of stage 1) during assembly. The assembly of the sealing sectors is carried out on the LP turbine casing, then the LP turbine casing is assembled in the flange 60 by approaching it from downstream to upstream. If the annular sectors 120 extend to the foot 70, or even beyond said foot 70, in order to protect it over its entire height, they do not extend radially to the distributors 20. Indeed, a radial clearance is maintained between the annular sectors and the distributors so as not to hinder the assembly of the sealing assemblies 100 and the distributors 20. This radial clearance may be a clearance of at least 1 mm, for example.

Front (drawing A) and rear (drawing B) views of the sealing assembly 100 are shown in FIG. . These views show the sealing sector 110 as described above and whose upstream end 114 is in contact with the annular sector 120. The annular sector 120 has a section substantially in the shape of an inverted T and comprises a radial wall 121 forming the arm of the inverted T shape and a substantially axial wall 122 forming the leg of the inverted T shape. The radial wall 121 extends annularly along the leg 71 of the shell foot 70 and comprises an upstream face 121a, facing said shell foot 70, and a downstream face 121b from which the axial wall 122 extends. The axial wall 122 may be axially rectilinear or, on the contrary, curved so as to have a projecting external end 122a. The radial wall 121 and the axial wall 122 participate in absorbing the forces transmitted by the sealing assembly 100 in the annular sector 120 without placing too much stress on the fixing zones (described below). Indeed, during operation, the flow of hot air from the vein 50 comes into contact with the internal part of the radial wall 121 and tends to tilt the annular sector. The axial wall 122 of the annular sector then participates in transmitting these forces to the sealing sector 110 opposite.

The annular sector 120 is fixed to the end of the sealing sector 110. It can, for example, be fixed by a double brazing, in two separate zones 141, 142, shown in the . One of the fixing zones 141, or brazing zone, can be located on the downstream face 121b of the radial wall 121, facing the upstream end 114 of the sealing sector 110. The other fixing zone 142 can be located on the external surface 122a of the axial wall 122. The fixing zone 141 thus ensures a radial fixing between the radial wall 121 of the annular sector 120 and a radial surface of the sealing sector 110 formed by the upstream end 114. The fixing zone 142 ensures an axial fixing between the axial wall 122 of the annular sector 120 and an axial surface of the sealing sector 110 formed by the internal surface of the annular portion 112. Regardless of the fixing zone 141 or 142, the brazing is carried out according to conventional techniques in the field of turbomachines, with classic materials.

In some embodiments, it is possible to shorten the sealing sector 110 so that its axial portion 112a is shorter, in the upstream direction, than for conventional sealing sectors. Such embodiments make it easier to attach the annular sector 120 to the upstream end 114.

According to a preferred embodiment of the invention, the angular sector 120 is produced by additive manufacturing, for example in MIM (Metal Injection Molding, in English terminology) or in Inconel® 718. The additive manufacturing of the angular sector 120 makes it possible to precisely determine the shape best suited to the geometry of the sealing sector 110 on which the annular sector will be fixed so as to obtain a contact seal between the two sectors 110, 120. The additive manufacturing also makes it possible to produce reinforcements, for example in the form of a rib or several honeycomb-shaped ribs, making it possible to withstand the static, thermal and dynamic stresses imposed by the sealing sector and the air flow of the vein 50.

The annular sectors 120, like the sealing sectors 110, are sectorized parts. They are therefore not subject to tangential stresses. Thus, extending the sealing sectors 110 by annular sectors 120 allows said annular sectors to act as a thermal barrier protecting the shell 10.

When assembled, the annular sectors 120 are positioned next to each other, as are the sealing sectors 110, so as to form a ring. Two adjacent annular sectors 120 are therefore juxtaposed and separated by a space called an intersector 120'. According to one embodiment, and in order to prevent leaks of the hot air flow through these intersectors, the sealing assembly 100 comprises a plurality of sealing plates 150, a sealing plate being positioned at each intersector 120'. An example of two adjacent sealing assemblies 100 is shown schematically in FIG. . This shows two sealing sectors 110 side by side and two annular sectors 120 each mounted on one of the sealing sectors. It also shows a sealing plate 150 mounted at the junction of the two annular sectors 120, i.e. in the intersector 120'. The sealing plate 150 is housed on either side in a cavity 123 formed within each of the annular sectors 120. Indeed, each annular sector 120 comprises two non-through cavities 123: a first cavity 123 opening at a first circumferential end 124a of a first annular sector 120 and a second cavity 123 opening at a second circumferential end 124b of the second annular sector 120, the first circumferential end 124a being opposite the second circumferential end 124b. The cavity 123 is located in the thickness of the radial wall 121 of the annular sector 120 and has dimensions adapted to partially receive a sealing plate 150.

When assembled, the sealing assemblies 100, arranged side by side circumferentially, form a ring of central axis A which protects the shell 10. In the embodiment comprising sealing plates 150 mounted in each intersector space 120', the sealing plates contribute to forming the thermal protection barrier by preventing any leakage of the hot air flow from reaching the shell. Thus, the hot air flow coming from the vein 50 licks the annular sectors 120, thermally protecting the foot 70 of the shell 10 over its entire height and over its entire circumference.

It is understood from the above that the invention has the consequence of increasing the service life of the shell 10, which allows a reduction in the maintenance cost of the LP turbine, in particular by saving the downtime of the turbine necessary for changing the shell 10.

Although described through a number of examples, variations and embodiments, the LP turbine sealing assembly according to the invention includes various variations, modifications and improvements which will be obvious to those skilled in the art, it being understood that these variations, modifications and improvements are part of the scope of the invention.

Claims (12)

A sealing assembly (100) for a low pressure turbine stator extending about a central axis (A), the sealing assembly (100) comprising a sealing sector (110) comprising:

• a base (111),
• a hook (113) extending from the base,
• an annular portion (112) extending radially projecting from an intersection of the base and the hook,

said sealing assembly (100) being characterized in that it further comprises an annular sector (120) extending radially from the annular portion (112) of the sealing sector (110) towards the central axis (A) and fixed to at least one end (114) of said sealing sector to form a thermal protection barrier. Sealing assembly according to claim 1, characterized in that the annular sector (120) has a section in the shape of an inverted T. Sealing assembly according to claim 1 or 2, characterized in that the annular sector (120) is fixed to the sealing sector (110) by a double brazing, in two separate zones (141, 142). Sealing assembly according to claims 2 and 3, characterized in that the annular sector (120) comprises a first fixing zone (142) located on an external surface of a leg of the T-shape and a second fixing zone (141) located on a downstream surface of an arm of the T-shape. Sealing assembly according to claim 3 or 4, in which the annular portion (112) of the sealing sector comprises a substantially L-shaped section with a radial part (112a) and an axial part (112b),
characterized in that the first fixing zone (142) is in contact with an internal surface of the axial part (112b) and the second fixing zone (141) is in contact with an end surface (114) of the radial part (112a). Sealing assembly according to any one of claims 1 to 5, characterized in that the annular sector (120) has a rounded shape with the same curvature as the sealing sector (110). Sealing assembly according to any one of claims 1 to 6, characterized in that the annular sector (120) is produced by additive manufacturing. Sealing assembly according to any one of claims 1 to 7, characterized in that the annular sector (120) comprises at least one cavity (123) opening at a circumferential end of said annular sector to receive a sealing plate (150). Low pressure turbine ring for a turbomachine, characterized in that it comprises a plurality of sealing assemblies (100) according to any one of claims 1 to 8, positioned circumferentially next to each other. Low pressure turbine ring according to claim 9, characterized in that it comprises, between two annular sectors (120), a sealing plate (150) partially housed in each of the two annular sectors. System for low pressure turbine of turbomachine, characterized in that it comprises:

• a ring according to any one of claims 9 and 10, comprising a plurality of sealing assemblies (100), and
• an annular ferrule (10) comprising a radially extending foot (70),

each sealing assembly (100) of the ring being positioned opposite the foot of the ferrule to form a thermal protection barrier. Turbomachine comprising a plurality of sealing assemblies (100) according to any one of claims 1 to 8.