Turbine shroud assembly with upstream annular flange for supporting the shroud and for compensating for differential expansion

Abstract

The invention relates to a turbine shroud assembly (2) comprising a plurality of shroud segments (10) made of ceramic matrix composite material, which form a turbine shroud (4) and define an axial direction (DA), a radial direction (DR), and a circumferential direction (DC), as well as a plurality of inter-segment junctions (100) in the circumferential direction (DC), wherein the turbine shroud assembly (2) further comprises a shroud support structure (6) having an upstream annular flange (20) and a downstream radial flange (64), between which each shroud segment (10) is axially and radially held, and wherein the upstream annular flange (20) is formed as a single annular part. The upstream annular flange (20) comprises, opposite each shroud segment (10), a circumferential expansion slot (80).

Description

[0001] Description

[0002] Title of the invention: Turbine ring assembly with upstream annular ring support flange with differential expansion compensation

[0003] Technical Field

[0004] The invention relates to a turbine ring assembly for a turbomachine in which the assembly comprises a plurality of angular ring sectors made of ceramic matrix composite material, and more particularly the invention relates to the ring support of the turbine ring assembly.

[0005] The field of application of the invention is in particular that of gas turbine aeronautical engines. The invention is however applicable to other turbomachines, for example industrial turbines.

[0006] Prior art

[0007] In the case of all-metal turbine ring assemblies, it is necessary to cool all the elements of the assembly and in particular the turbine ring which is subjected to the hottest flows. This cooling has a significant impact on the engine performance since the cooling flow used is taken from the primary flow of the engine. In addition, the use of metallic material for the turbine ring limits the possibilities of increasing the temperature at the turbine level due to the mechanical limitations specific to this type of material, which would nevertheless improve the performance of aeronautical engines.

[0008] In an attempt to resolve these problems, consideration was given to making the turbine ring from ceramic matrix composite (CMC) material in order to avoid the use of a metallic material.

[0009] CMC materials have good mechanical properties making them suitable for forming structural elements and advantageously retain these properties at high temperatures. The use of CMC materials has advantageously made it possible to reduce the cooling flow required during operation and therefore to increase the performance of turbomachines. In addition, the use of CMC materials advantageously makes it possible to reduce the mass of turbomachines and to reduce the effect of hot expansion encountered with metal parts. Documents FR 2 540 939 and FR 2 955 898 are also known, which disclose turbine ring assemblies.

[0010] The ring comprises an annular base whose inner face defines the inner face of the turbine ring and an outer face from which two legs extend radially, the ends of which are held between the two flanges of a metal ring support structure.

[0011] The integration of a CMC ring includes radial support of the part partly ensured by one or more axial pins. In the known document FR 3 086 327, there are four pins, two upstream and two downstream.

[0012] Using a CMC material for the ring significantly reduces the ventilation required to cool the turbine ring, thus increasing efficiency. They also allow for weight savings because they are lighter than the metal alloys traditionally used.

[0013] However, since CMC has a different mechanical behavior from a metallic material, its integration and the way of positioning it within the turbine had to be rethought. Indeed, CMC can be damaged by shrink-fit assemblies (usually used for metallic rings) and its thermal expansion is lower than that of a metallic material.

[0014] There is a need to improve existing turbine ring assemblies and their mounting, and in particular existing turbine ring assemblies using CMC material to reduce the intensity of mechanical stresses to which the CMC ring is subjected during turbine operation.

[0015] CMC turbine rings are generally divided into several ring sectors. This integration choice is due to the fact that a single-piece ring would deform under the effect of high temperatures for this high-pressure turbine part. This would result in a clearance at the tip of the moving blade (in the opposite vein) that is locally too large and thus significantly degraded performance via a loss of turbine efficiency.

[0016] The consequence of this sectorization of the turbine ring is the creation of inter-sector clearances (between 0.1 mm and 1 mm). To limit leaks in these areas, sealing strips (also called sheets) are generally integrated between the ring sectors.

[0017] The ring support for holding the CMC ring is generally made of metal and fixed to a casing. The ring support comprises a central shell from which an upstream element and a downstream element project radially inward, between which the CMC turbine ring is intended to be held at least axially. The downstream element may be a downstream radial flange machined from the same part as the central shell, or a downstream annular flange fixed to an attachment element of the central shell of the ring support. On the other hand, the upstream element is, in general, an upstream annular flange fixed to an attachment element of the central shell of the ring support or to a reduced-sized upstream radial flange.

[0018] The upstream element of the ring support, which is generally the upstream flange, undergoes, in addition to the mechanical stresses due to the forces transmitted by the DHP, a significant thermal gradient between the internal diameter which is approximately 800 °C and the external diameter which is approximately 500 °C. This significant thermal gradient generates significant circumferential stresses in the upstream annular flange.

[0019] These constraints are accentuated by the activation of the active play control (HPTACC) which is often problematic for the dimensioning of the part and makes it necessary to cut it tangentially or circumferentially, that is to say a division of the annular flange into a plurality of ring sectors. The sectorization of the upstream annular flange into a plurality of ring sectors allows each ring sector to expand freely tangentially, in other words in the circumferential direction, and to move more easily radially in the case of activation of the HPTACC.

[0020] Unfortunately, sectoring the upstream annular flange increases the risk of leakage between the CMC ring cavity and the flow vein inside the channel formed by the ring assembly, which poses a problem given that the ring support also has the role of maintaining a seal between the vein and the non-vein area.

[0021] Statement of the invention The main aim of the present invention is therefore to propose a turbine ring assembly which does not have the aforementioned drawbacks and which makes it possible both to maintain a seal of the ring support comparable to that provided by an upstream annular flange and to improve the adaptation of the ring support to the circumferential stresses generated by the radial thermal gradients.

[0022] This aim is achieved by means of a turbine ring assembly comprising a plurality of ring sectors made of ceramic matrix composite (CMC) material forming a turbine ring defining an axial direction, a radial direction and a circumferential direction, the ring sectors being arranged end-to-end in the circumferential direction, defining between them, two by two, an intersector junction in the circumferential direction, the turbine ring assembly further comprising a ring support structure comprising an upstream annular flange and a downstream radial flange between which each ring sector is held, the upstream annular flange being made in a single annular part.

[0023] The turbine ring assembly according to the invention is remarkable in particular in that the upstream annular flange comprises, axially opposite each ring sector, an expansion slot extending longitudinally in the circumferential direction.

[0024] Preferably, the expansion slots pass right through the upstream annular flange in the axial direction.

[0025] The incorporation of expansion slots in the upstream annular flange makes it possible to maintain a non-sectorized annular flange and thus to ensure a seal equivalent to that offered by a single-piece annular flange, while offering a new possibility for the upstream annular flange to deform in response to the higher temperatures experienced on the inner diameter of the annular flange. Indeed, the circumferential cutouts, or slots, make it possible to increase the heat exchange surface with the cooling air circulating between the ring support and the turbine ring, and therefore to better cool the radially inner part of the ring support and therefore to reduce thermal stresses.

[0026] In other words, the upstream annular flange according to the invention makes it possible to maintain an integral external diameter (in a single piece without disjunction) and to ensure good sealing, while offering options for deformation and adaptation in response to the temperature gradient observed between the hot part close to the vein and the less hot part far from the vein. The use of a non-sectorized upstream annular flange makes it possible to limit leaks on the radially external part which are of the order of 15% of the total sampling flow rate.

[0027] The non-sectored upstream annular flange thus reduces air leaks towards the upper cavity between the support and the casing, which can be observed with a sectored upstream annular flange in particular. This air flow can be returned to the shower to better cool the ring and then the lower part of the upstream support, where the temperature levels are higher.

[0028] When hot, the different parts of the ring support will expand and come into contact, which will allow the expansion slots to be closed.

[0029] Preferably, each ring sector comprises a base from which an upstream hooking lug and a downstream hooking lug extend radially outwardly, axially spaced from each other. The upstream hooking lug and a downstream hooking lug are held between the upstream annular flange and the downstream radial flange of the ring support structure.

[0030] Preferably, each expansion slot extends, in the circumferential direction, between two inter-sector junctions and over a length strictly less than the length of a ring sector in the circumferential direction.

[0031] According to a first aspect of the turbine ring assembly, each zone of the upstream annular flange arranged axially opposite an inter-sector junction is devoid of an expansion slot. In other words, no circumferential expansion slot extends in each zone of the upstream annular flange arranged axially opposite an inter-sector junction.

[0032] The annular flange areas without expansion slots ensure mechanical support for the upstream annular flange, in other words, ensure that the upstream annular flange holds itself. In addition, the arrangement of the annular flange areas without expansion slots axially opposite the inter-sector junctions makes it possible to maintain good inter-sector sealing between the turbine ring and the ring support, in particular thanks to the axial tightening of the ring support with the turbine ring.

[0033] According to a second aspect of the turbine ring assembly, each expansion slot may be arranged radially outside an axial bearing zone between the upstream annular flange and the turbine ring, and radially outside a bearing zone between the upstream annular flange and a distributor intended to be placed upstream of the upstream annular flange.

[0034] This arrangement ensures that the seal is maintained throughout the operation of the turbine.

[0035] According to a third aspect of the turbine ring assembly, each expansion slot may have at least one radial corrugation so as to extend over different radial positions. In other words, each expansion slot may have one or more radial corrugations extending over different radial positions.

[0036] Preferably, the radial corrugation has a half-lyre shape. In other words, the circumferential expansion slot extends along a first radial position, or at a first radius, then, at the radial corrugation, the expansion slot extends radially outward or inward and then returns to the first radial position. In other words, the radial corrugation provided in the expansion slot is equivalent to a step of the expansion slot on another radius at a given circumferential position.

[0037] This radial undulation, that is to say the half-lyre shape, makes it possible to accept deformations in all directions, whether axial, radial, circumferential or even gyration, which are due to temperature differences between the radially inner end of the upstream annular flange and its radially outer end.

[0038] According to a fourth aspect of the turbine ring assembly, the upstream annular flange may comprise, axially opposite each ring sector, a radial slot open on an inner radial end of the upstream annular flange, each radial slot extending radially from the inner radial end to at least the expansion slot, each radial slot being arranged in the circumferential direction between two circumferentially adjacent inter-sector junctions. Preferably, each radial slot is arranged in the circumferential direction equidistant from the two circumferentially adjacent inter-sector junctions.

[0039] The open radial slot on an inner radial end of the downstream radial flange provided in each housing allows for semi-sectorization of the downstream radial flange and thus allows it to better conform to the constraints and thus further limit shear.

[0040] According to a fourth aspect of the turbine ring assembly, each expansion slot may have two radial undulations symmetrically arranged, in the circumferential direction, on either side of an associated radial slot.

[0041] In another embodiment, the upstream annular flange may comprise axial fastening holes, each axial fastening hole being arranged radially outside a radial undulation.

[0042] In another embodiment, the upstream annular flange may comprise an auxiliary axial orifice arranged, in the circumferential direction, between two axial fixing orifices and, in the radial direction, outside a radial slot, the auxiliary axial orifice having an oblong shape with a major axis extending in the circumferential direction.

[0043] The invention also relates to a turbomachine comprising an assembly as defined above.

[0044] The invention can be applied to any turbine stage comprising a ring made of ceramic matrix composite material.

[0045] Brief description of the drawings

[0046] [Fig. 1] Figure 1 is a schematic sectional view along a plane including the axial direction and the radial direction of a turbine ring assembly according to the invention.

[0047] [Fig. 2] Figure 2 shows an exploded perspective view of a portion of the ring support of the turbine ring assembly of Figure 1.

[0048] [Fig. 3] Figure 3 shows an assembled perspective view of a portion of the ring support of the turbine ring assembly of Figure 1.

[0049] Description of the embodiments Figure 1 schematically represents a turbine ring assembly 2 according to a first embodiment of the invention. Figure 1 is a sectional view along a plane comprising the radial direction DR and the axial direction D A and orthogonal to the circumferential direction D c .

[0050] The turbine ring assembly 2 shown in Figures 1 and 2 includes in particular a turbine ring 4 made of ceramic matrix composite (CMC) material centered on a longitudinal axis XX, a metal ring support structure 6 fixed to a turbine casing not shown for clarity. The turbine ring 4 surrounds a set of turbine blades not shown. The circumferential direction D c is a circular direction centered on the longitudinal axis XX.

[0051] Subsequently, throughout the text, the terms "upstream" and "downstream" are used in reference to the direction of flow of the gas stream F through the blades indicated by an arrow.

[0052] Furthermore, the turbine ring 4 is formed from a plurality of angular ring sectors 10 which are placed end to end in the circumferential direction to form a ring. In Figure 1, the arrow D Aindicates the axial direction of the turbine ring while arrow D R indicates the radial direction of the turbine ring.

[0053] Each angular ring sector 10 has a section substantially in the shape of an inverted Pi (or ii) with a base 12 provided with an internal face 12a which defines an angular portion of the internal face of the turbine ring 4 and which is typically provided with a layer of abradable coating 13 also acting as a thermal and environmental barrier.

[0054] Two axially spaced attachment lugs, a downstream attachment lug 14 and an upstream attachment lug 16, extend radially from the outer face 12b of the base 12 opposite the inner face 12a. These attachment lugs 14 and 16 extend over the entire width of each ring sector 10 (in the circumferential direction).

[0055] The ring support structure 6 comprises a ferrule 60 extending around the axis XX, as well as an upstream radial flange 62 and a downstream radial flange 64 extending radially inward from the ferrule 60. The downstream radial flange 64 comprises a downstream attachment portion 640 projecting radially from the ferrule 60 and an annular flange 642 fixed to the downstream attachment portion 640, and the upstream radial flange 62 comprises an upstream attachment portion 620 projecting radially from the crown 60, as well as an upstream annular flange 20 fixed to the upstream attachment portion 620.

[0056] The upstream radial flange 62 and the downstream radial flange 64 thus form two attachment flanges for the ring 4, the downstream attachment lug 14 and the upstream attachment lug 16 of the ring sectors 10 being arranged axially between the upstream radial flange 62 and the downstream radial flange 64.

[0057] The turbine ring assembly 2 further comprises upstream pins and downstream pins not shown to simplify reading of the figures. The upstream pins pass through the upstream annular flange 20 of the upstream radial flange 62 as well as the upstream lug 16 of a ring sector 10. The downstream pins pass at least partially through the downstream radial flange 64, and more particularly the radially projecting attachment portion 640, as well as the downstream attachment lug 14.

[0058] Furthermore, the turbine intended to comprise the ring assembly 2 comprises a downstream distributor 30 bearing against the downstream radial flange 64, as well as an upstream distributor, not shown, bearing against an upstream face 8 of the upstream annular flange 20. The downstream distributor 30 is located downstream of the downstream radial flange 64 while the upstream distributor is located upstream of the upstream annular flange 20.

[0059] In Figure 2 is shown a front view of a portion of the upstream annular flange of the ring assembly 2 of Figure 1, and in Figure 3 is shown a front view of a portion of the ring assembly 2 of Figure 1.

[0060] The upstream annular flange 20 comprises an inner radial end 201, an outer radial end 202, fixing orifices 203, a radial semi-sectoring slot 70 and circumferential expansion slots 80.

[0061] As shown in Figure 3, the fixing holes 203 are intended to be passed through by screws 210 to fix the upstream annular flange 20 to the attachment portion 620 of the upstream radial flange 62 of the ring support 6.

[0062] As illustrated in Figure 2, each circumferential expansion slot 80 passes right through the upstream annular flange 20 in the axial direction D and is arranged opposite a ring sector 10. As illustrated in Figure 3, each circumferential expansion slot 80 extends, in the circumferential direction D c , opposite a ring sector 10 and over a length strictly less than the length of the ring sector 10.

[0063] Two adjacent circumferential slots 80 along the circumferential direction D c are separated in this direction by a zone 82 without a circumferential expansion slot, called the opaque zone hereinafter. In the axial direction D A , each opaque zone 82 is arranged opposite an inter-sector junction 100 of the turbine ring 4.

[0064] The upstream annular flange 20 comprises an upstream face 204, visible in particular in FIGS. 2 and 3, and a downstream face 207. On each of the upstream 204 and downstream 207 faces, the upstream annular flange 20 comprises an axial bearing zone 206 extending radially from the inner radial end 201. The axial bearing zone 206 on the upstream face 204 bears against a portion of the upstream distributor while the axial bearing zone 206 on the downstream face of the upstream annular flange 20 bears against the upstream attachment lugs 16 of the ring sectors 10 of the turbine ring 4.

[0065] Each circumferential slot 80 is arranged radially outside the axial support zones 206 to ensure that the seal is maintained throughout the operation of the turbine.

[0066] As shown in Figures 2 and 3, each circumferential slot 80 comprises two radial undulations 84. The radial undulation 84 has a half-lyre shape. The circumferential expansion slot 80 extends mainly along a first circle having a first radius. It further forms, at the radial undulation 84, a step, that is to say that it no longer follows the perimeter of the first circle, but, by moving along the circumferential direction D c , it dips radially inward to a radial height further inward than the first circle, then rises radially outward to the height of the first circle.

[0067] Each semi-sectoring radial slot 70 is open on the inner radial end 201 of the upstream annular flange 20 and extends from the inner radial end 201 to the circumferential expansion slot 80. As illustrated in FIGS. 2 and 3, each semi-sectoring radial slot 70 is arranged in the circumferential direction D c equidistant from the two circumferentially adjacent inter-sector junctions 100. And, the two radial undulations 84 of the same circumferential expansion slot are located, in the circumferential direction D c , symmetrically relative to each other with respect to the associated semi-sectoring radial slot 70.

[0068] The upstream annular flange 20 comprises an auxiliary axial orifice 205 arranged, in the circumferential direction D c, between two fixing orifices 203 and, in the radial direction DR, outside a radial slot 70, the auxiliary axial orifice 205 having an oblong shape with a major axis extending in the circumferential direction D c .

[0069] The present invention thus provides a turbine ring assembly making it possible both to maintain a seal of the ring support comparable to that provided by an upstream annular flange and to improve the adaptation of the ring support to the circumferential stresses generated by radial thermal gradients.

Claims

Claims

1. Turbine ring assembly (2) comprising a plurality of ring sectors (10) made of ceramic matrix composite material forming a turbine ring (4) defining an axial direction (D A ), a radial direction (D R ) and a circumferential direction (D c ), the ring sectors (10) being arranged end-to-end in the circumferential direction, defining between them, two by two, an intersector junction (100) in the circumferential direction (D c), the turbine ring assembly (2) further comprising a ring support structure (6) comprising an upstream annular flange (20) and a downstream radial flange (64) between which each ring sector (10) is held, the upstream annular flange (20) being made in a single annular piece, characterized in that the upstream annular flange (20) comprises, axially opposite each ring sector (10), an expansion slot (80) extending longitudinally in the circumferential direction (De).

2. A turbine ring assembly (2) according to claim 1, wherein each expansion slot (80) extends, in the circumferential direction (D c ), between two inter-sector junctions (100) and over a length strictly less than the length, in the circumferential direction (D c ), of a ring sector (10).

3. Turbine ring assembly (2) according to one of claims 1 or 2, in which each zone (82) of the upstream annular flange (20) arranged axially opposite an inter-sector junction (100) is devoid of an expansion slot.

4. Turbine ring assembly (2) according to one of claims 1 to 3, in which each expansion slot (80) is arranged radially outside an axial support zone (206) between the upstream annular flange (20) and the turbine ring (4), and radially outside a support zone (206) between the upstream annular flange (20) and a distributor intended to be placed upstream of the upstream annular flange (20).

5. Turbine ring assembly (2) according to one of claims 1 to 4, in which each expansion slot (80) has at least one radial undulation (84) so ​​as to extend over different radial positions.

6. Turbine ring assembly (2) according to one of claims 1 to 5, in which the upstream annular flange (20) comprises, axially opposite each ring sector (10), a radial slot (70) which opens onto a radially inner end (201) of the upstream annular flange (20), each radial slot (70) extending radially from the radially inner end (201) to an expansion slot (80), each radial slot (70) being arranged in the circumferential direction (D c ) between two circumferentially adjacent inter-sector junctions (100).

7. A turbine ring assembly (2) according to claim 6, wherein each radial slot (70) is arranged, in the circumferential direction (D c ), equidistant from two circumferentially adjacent inter-sector junctions (100).

8. Turbine ring assembly (2) according to one of claims 6 or 7, in which each expansion slot (80) has two radial undulations (84) symmetrically arranged, in the circumferential direction (D c ), on either side of a radial slot (70).

9. Turbine ring assembly (2) according to claim 8, in which the upstream annular flange (20) comprises axial fixing orifices (203), each axial fixing orifice (203) being arranged radially outside a radial undulation (84).

10. Turbine ring assembly (2) according to claim 9, in which the upstream annular flange (20) comprises an auxiliary axial orifice (205) arranged, in the circumferential direction (D c ), between two axial fixing holes (203) and, in the radial direction (D R), outside a radial slot (70), the auxiliary axial orifice (205) having an oblong shape extending longitudinally in the circumferential direction (De).

11. Turbomachine comprising an assembly (2) according to any one of claims 1 to 10.

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