FR3083566A1 - TURBINE ASSEMBLY FOR AN AIRCRAFT TURBOMACHINE WITH A DISC COOLING CIRCUIT HAVING A SEALING DEVICE - Google Patents

Abstract

The invention relates to a turbine assembly for an aircraft turbomachine, comprising a disc (17) carrying rotary vanes (18), an axial retention device for the vanes on this disc including an axial retaining member (32) for the maintained vanes. in abutment against the disc and the blades by a bearing end (34) of an annular flange (33), and a sealing device comprising at least one sealing element (48) which includes a first portion of fastener clamped axially between the disc (17) and the axial retaining member (32), and a sealing portion which extends the first fastening portion by extending towards the flange (33) to be in contact with this flange (33).

Description

TURBINE ASSEMBLY FOR AN AIRCRAFT TURBOMACHINE WITH DISC COOLING CIRCUIT HAVING A SEALING DEVICE DESCRIPTION

TECHNICAL AREA

The invention relates to a turbine assembly for an aircraft turbomachine, and more specifically to the problem of cooling a rotor disc.

PRIOR STATE OF THE ART

In a turbomachine, the turbine blades placed downstream of the combustion chamber are subjected to severe temperature conditions. For this purpose, it is known to cool these blades with a cooling fluid, generally air, admitted at the foot of the blade to travel along an internal circuit and evacuated out of the blade by holes distributed over its aerodynamic walls.

In practice, the increased performance requirements of turbomachines imply increasing the temperatures at the outlet of the combustion chamber still further, thus leading to also considering the cooling of the turbine disks carrying the blades. Document FR2825748 is known to provide this cooling with air, taken upstream from the turbine, which circulates in passages delimited between the blade roots and grooves formed in the disc and in which these feet are installed. , as well as in spaces defined between the disc and an annular flange. This flange, integral in rotation with the disc, participates in particular in maintaining the blade in position by pressing an axial retaining ring against the disc and the root of the blades.

It has however been observed that air escapes from the spaces defined for the propagation of the cooling air, in particular at the interface between the flange and the retaining ring. It being understood that any exhaust of air does not participate in the cooling of the disc, there is a need to ensure a satisfactory seal. This sealing problem is all the more complex the smaller the space provided between the flange and the disc / the blades.

The object of the invention is therefore to propose a solution making it possible to limit these leaks, in other words to force the flow of fresh air to marry the surface of the disc by borrowing the spaces defined between this disc and the flange.

STATEMENT OF THE INVENTION

To this end, the subject of the invention is a turbine assembly for an aircraft turbomachine, comprising:

- A rotor disc which extends around an axis, the disc being extended axially along the axis by a flange and carrying a plurality of radial vanes each comprising a foot engaged in a corresponding axial groove formed at the periphery of the disc , with each pair formed by a groove and a foot defining between them an axial air flow channel;

- an annular flange, fixed to the flange, extending axially towards the disc and which has an annular end extending radially outwards beyond the air flow channel by delimiting jointly with the flange a passage air communicating with the air flow channel;

- An axial retaining member of the blades in their corresponding groove, which is disposed against the disc by the annular flange;

this turbine assembly being characterized in that it comprises a sealing device including at least one sealing element, this sealing element including:

a first attachment portion clamped axially between the disc and the axial retaining member, and

- A sealing portion which extends the first attachment portion by extending towards the flange to be in contact with this flange.

The invention thus makes it possible to meet the need formulated above, by providing a sealing device comprising at least one sealing element forming a barrier thus preventing air from escaping at the interface between the flange ring and the retaining member.

The invention also relates to an assembly thus defined, in which the sealing element is a sheet, with the first attachment portion and the sealing portion which form an obtuse angle in a view in section along a plane passing through the axis of the disc.

The invention also relates to an assembly thus defined, in which the sealing element is a sheet having a U-shaped profile in a sectional view along a plane passing through the axis of the disc, comprising a second portion d 'fastener which extends the sealing portion by being clamped between the annular end of the flange and the axial retaining member.

The invention also relates to an assembly thus defined, in which the sheet thickness is from 0.1mm to 0.5mm.

With this solution, the mass introduced by the addition of the sealing element is significantly limited.

The invention also relates to an assembly thus defined, in which the axial retaining member of the blades is pressed against the disc by the annular flange at the inner periphery of this axial retaining member.

The invention also relates to an assembly thus defined, in which the device comprises a single annular sealing element or several sealing elements extending circumferentially while being arranged end-to-end.

The invention also relates to an assembly thus defined, in which:

the axial retaining member comprises an alternation between solid parts each extending circumferentially along at least one blade root and pressed towards the disc by the annular end of the flange, and recessed parts extending each in an angular sector delimited between two successive feet; and

- The first attachment portion of the sealing element covers the disc at the level of the recessed part (s) located axially opposite this sealing element.

With this arrangement, the invention is an extension of the overall reduction effort of the mass of the turbine assembly while retaining control over the sealing of the disc cooling circuit.

The invention also relates to an assembly thus defined, in which the axial retaining member is continuous along its outer periphery.

The invention also relates to a turbine for an aircraft turbomachine comprising at least one assembly thus defined, the turbine preferably being a low pressure turbine.

The invention also relates to an aircraft turbomachine comprising at least one turbine thus defined, the turbomachine preferably being a double-body turbomachine.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made with reference to the attached drawings, in which:

- Figure 1 is a block diagram of a turbofan engine in axial section according to the invention;

- Figure 2 illustrates a schematic half-view of a low pressure turbine of a turbomachine according to the invention;

- Figure 3 partially shows, in exploded view and schematically, a disc equipped with a blade according to the invention;

- Figure 4 is a detail view of Figure 2 illustrating a turbine assembly comprising a movable wheel followed by a distributor;

- Figure 5 is a partial perspective view of a turbine assembly with a radially continuous blade axial retaining member which is subject to a leakage problem;

- Figure 5A shows a sectional view of Figure 5 along a PI plane, illustrating a problem of leakage;

- Figure 6 is a partial perspective view of a turbine assembly according to a first embodiment of the invention;

- Figures 6A and 6B show sectional views of Figure 6 along the plane P2, with Figure 6B illustrating in particular the conservation of the seal under dimensional variation;

- Figure 7 is a partial perspective view of a turbine assembly according to a second embodiment of the invention;

- Figures 7A and 7B show sectional views of Figure 7 along the plane P3, with Figure 6B illustrating in particular the conservation of the seal under dimensional variation;

- Figure 8 is a partial perspective view of a turbine assembly, with an axial blade retaining member, comprising an alternation of solid parts and hollow part, which is subject to a leakage problem;

- Figures 8A and 8B show sectional views of Figure 8, respectively at a part hollowed out according to the plane P4, and a solid part according to the plane P5;

- Figure 9 is a partial perspective view of a turbine assembly according to a third embodiment of the invention;

- Figures 9A and 9B show sectional views of Figure 9, at the level of a hollowed part respectively according to the plane P6, and a solid part according to the plane P7;

- Figure 10 is a partial perspective view of a turbine assembly according to a fourth embodiment of the invention;

- Figures 10A and 10B show sectional views of Figure 10, respectively at a part hollowed out according to the plane P8, and a solid part according to the plane P9.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Referring to Figure 1, there is shown an aircraft turbomachine 1, according to a preferred embodiment of the invention. This is a double-flow, double-body turbojet engine. However, it could be a turbomachine of another type, for example a turboprop, without departing from the scope of the invention.

The turbomachine 1 has a central axis AX around which its various components extend. It comprises, from upstream AM downstream AV in a main direction 5 of gas flow through this turbomachine, a blower 3, a low pressure compressor 4, a high pressure compressor 6, a combustion chamber 7, a high turbine pressure 8 and a low pressure turbine 9.

Conventionally, after passing through the blower, the air is divided into a central primary flow 11a and a secondary flow 11b which surrounds the primary flow. The primary flow 11a flows in a main stream 12a for gas circulation passing through the compressors 4, 6, the combustion chamber 7 and the turbines 8, 9. The secondary stream 11b flows in turn in a secondary stream 12b delimited radially outwards by a motor housing, surrounded by a nacelle 13.

FIG. 2 represents a part of the low pressure turbine 9. However, the invention could also apply to the high pressure turbine 8, without going beyond the ambit of the invention. This low pressure turbine 9 comprises a rotor 14 including a plurality of wheels, here identified by 16 and four in number by way of example, fixed to each other by clamping 15 and each comprising a disc 17, of axis of revolution AX, carrying a cascade of rotary vanes 18. As is better visible in FIG. 3, these vanes 18 distributed circumferentially around the disc 17 each include an aerodynamic part 19, also called a blade, a foot 21 and a platform 22 which connects the paddle at the foot. The blades are installed on the disc 17 by engaging in grooves 23 formed at the periphery of the latter, the grooves being regularly spaced from each other by delimiting two by two a tooth marked by 24. With their outer surface 25, the platforms 22 thus delimit radially inward the main vein 12a.

The turbine has in particular between each pair of two successive wheels 16 a distributor 26 comprising an annular row of fixed vanes 27. These fixed vanes are mounted at their radially external ends relative to the axis AX on an external turbine casing 28 surrounding this low pressure turbine 9, and at their radially internal ends by fixed ferrule sectors 29.

For the rest, a turbine assembly comprising a rotary disc 17 followed by a distributor 26 will be described in an upstream-downstream direction, with reference to FIGS. 4 and 5. It should be noted that the invention as it will be described can be applied to all the discs of the turbine, or only to some of them, the upstream / downstream designation can therefore be modified according to the position of the disc and / or the direction of insertion of the feet. blade 21 in the grooves 23 provided for this purpose.

The platform 22 of the rotary vanes 18 has two opposite axial ends, each forming a spoiler or flange. It is a downstream spoiler 31 located downstream AV and an upstream spoiler (not shown) located upstream of the blade 19. The axial locking, in other words along AX, of the rotary vanes 18 on the disc 17 is ensured by an axial retention device. This axial retention device comprises a member 32 for axial retention of the blades which is installed centered against a peripheral downstream part of the disc 17 and an annular flange 33. The member 32 is axially fixed on the blades at its outer periphery 32a, engaged in a cavity 30 provided for this purpose at the platforms 22 of the blade. It is also pressed axially against the disc 17 and in particular the downstream faces of the feet 21 at its internal periphery 32b by the flange 33.

More precisely, the flange 33 extends, from a flared annular end 34 of axial support of the retaining member 32 against the disc, downstream, surrounding and following the contour of a downstream fixing flange 36. This downstream fixing flange 36 in particular protrudes from the disc 17 to secure it to the next disc (not shown) also extended by an upstream flange 37, the downstream and upstream flanges 36 and 37 mating together by enclosing a fixing ring 39 flaccid.

The flange 33, in addition to ensuring the retention of the retaining member 32 in tight support against the disc 17, is provided with wipers 38a and 38b which cooperate with a block of abradable material 41 carried by the associated ferrule sector 29 at the stationary vane 27 of the distributor so as to form a labyrinthine seal. This flange 33 also participates in a cooling function of the disc 17 by delimiting with the flange 36 an air flow passage 42 which communicates with an axial air flow channel 43, delimited by the foot 21 and the groove 23 in which he is engaged. The axial channel 43 and the passage 42 jointly form a circuit for cooling the disc 17. It is understood here that the axial bearing end 34 and the retaining member 32 extend radially outwardly to the axial channel 43 to allow a fluid communication between the latter and the passage 42.

The disc 17, the retaining member 32 and the flange 33 are dimensioned so as to be consecutively in tight support once installed in series in the turbomachine. However, it has been noted the appearance of air leaks identified by F escaping outside the disc cooling circuit, in particular at the interface between the retaining member 32 and the flange 33. Indeed, a linear contact of the bearing end 34 on the retaining member 32 is not always ensured, on the one hand, due to possible surface roughness, and on the other hand, due to the phenomenon of differential expansion. In the latter case, the different dimensional variations of the disc, of the retaining member and of the flange in the operating temperature range of the turbomachine, can therefore induce a clearance identified by J in FIG. 5A.

The idea underlying the invention is thus to ensure good sealing of the cooling circuit of the disc. In this regard, the major feature of the invention lies in the addition of a sealing device which forms an obstacle preventing the quantity of air F from escaping.

With reference to FIGS. 6, 6A and 6B, according to a first embodiment of the turbine assembly, the sealing device relates to an annular sealing element, identified by 48, extending circumferentially along the retaining member which is in the form of a continuous ring of material over 360 °.

In view of the small space provided between the flange 33 and the disc 17, and aiming to limit the mass introduced into the turbomachine, this sealing element 48 is a sheet of thin thickness, preferably of the order of 0.1 to 0 , 5mm. It includes a first attachment portion 49 intended to be clamped axially between the disc / the blades and the retaining member 32. A sealing portion 51 extends the first attachment portion 49 by extending radially towards the inside the passage and axially towards the annular flange 33 to contact it, in a nonlimiting manner at the level of the support end 34. This sealing portion 51 ensures continuity of material between the disc 17 and the retaining member 32, preventing air from leaving in particular at the interface between this retaining member and the flange. Along the circumferential extent of the sealing element 48, the first attachment portion 49 and the sealing portion 51 are in the form of two straight segments forming an obtuse angle in a sectional view along a plane passing through the axis AX. In a nonlimiting manner, the invention advantageously provides that the sealing element 48 is pre-stressed during its installation, in other words with the first attachment portion and the sealing portion forming an angle greater than that they form before installation. With this arrangement, it is understood that the contact of the sealing portion 51 against the flange 33 can be maintained, via the effect of the elastic return identified by E in FIG. 6B, under geometric variations of the turbine assembly due at variable operating temperatures.

According to a second embodiment illustrated in FIGS. 7, 7A and 7B, the turbine assembly differs from the first embodiment in that the sealing element identified here by 48 ′ is in the form of a sheet having a U-shaped profile. This element 48 ′, with a preferential thickness of the order of 0.1 to 0.5 mm, also includes a first attachment portion 49 ′ which is axially clamped between the disc / the blades and the retaining member 32, and a sealing portion 51 ′ which extends in a mainly axial direction towards the flange 33 in order to contact it, in particular at the level of the bearing end 34. It also includes a second portion d 'fastener 52' which extends the sealing portion 51 'while being clamped between the annular end 34 of the flange 33 and the retaining member 32. As in the first embodiment, the invention advantageously provides that this element d 'waterproofing 48' is mounted pre-stressed, with the es first and second attachment portions extending not parallel to each other, but forming before installation an angle similar to that formed by the letter V. With this arrangement, it is understood that in the case of 'an appearance of a clearance J under geometric variations, a contact between the sealing element 48' and the flange 33 can be maintained at the level of the second attachment portion 52 'with the elastic return identified by E tending to that the sealing element regains its initial shape as illustrated in FIG. 7B.

Due to its morphology, the sealing element 48 according to the first embodiment of the invention makes it possible to direct the air flow, with its sealing portion 51 forming a ramp. As regards the sealing element 48 ′ according to the second mode, this is more resistant and better maintained than in the case of the first mode, in return however for an addition of material inducing an increase in mass to form the second attachment portion 52 '. It should be noted that this increase in mass compared to the first embodiment remains almost negligible when this element is a thin sheet.

It has recently been proposed to modify the shape of the member 32 for axially retaining the blades, in particular with a view to reducing the overall mass of the turbomachine, by making recesses therein. In the example of FIGS. 8, 8A and 8B, the retaining member 32 is in the form of a continuous rod along its outer periphery 32a, and discontinuous along its inner periphery 32b with alternating parts solid 46 and recessed parts 47. In practice, each solid part 46 extends circumferentially at least along a blade, radially overlapping both the disc 17 and the foot 21, and therefore extending in the extension axial of the annular end 34 of the flange, to ensure the axial retaining function of the blades under the pressing force of the flange as visible in FIG. 8B. Each hollowed out part is situated in a circumferential sector delimited between two successive feet 21. The support end 34 thus does not contact the axial retaining member 32 at the level of the recessed portions 47. With this architecture, it is understood here that the problematic of the invention remains intact while being exacerbated by the fact that air can escape at any time and for any temperature range at the level of these recessed portions 47, as illustrated by thick arrows in FIG. 8 and visible in more detail in FIG. 8A. It therefore becomes essential to ensure good sealing, in particular in the areas not covered, to force the flow of fresh air to marry the surface of the disc 17 by passing through the passage 42.

Concretely, the sealing device according to the invention also finds its application for such a retaining member architecture 32. In this respect, according to a third embodiment of the turbine assembly as illustrated in FIGS. 9 , 9A and 9B, the retaining member 32 includes such an alternation of solid parts 46 and hollow parts 47 as illustrated in FIG. 8, in association with a sealing element 48 whose morphology is similar to that described in the first embodiment. In addition, the invention advantageously provides that the first attachment portion 49 covers the disc at the level of the recessed portions 47. More specifically, this first attachment portion 49 extends radially beyond the recessed portions located axially in screw vis-à-vis the sealing element to be continuously enclosed between the outer periphery 32a of the retaining member 32 and the disc / blades over the entire circumferential extent of the retaining member. A better waterproof covering is thus obtained with this arrangement. However, it should be noted that the invention is not limited to this particular morphology aiming to maximize the contact surface and thus to limit any risk of leakage, and makes it possible to limit the radial extent of this first attachment portion 49 as long as there is still contact between it and the disc / vanes preventing air from escaping.

With reference to FIGS. 10, 10A and 10B, the turbine assembly according to a fourth embodiment differs from the third embodiment in that it comprises a sealing device with a sealing element 48 ′ whose morphology is similar to that provided in the second embodiment. In the same way, the invention advantageously provides, and is not limited to, that the first attachment portion marked with 49 ′ completely covers the disc 17 at the level of the recessed parts 47 in order to obtain a better sealed covering.

It should be noted that the increase in mass of the sealing element, induced by the preferential radial elongation of the first attachment portion 49 or 49 ′ in the context of the third and fourth embodiments, remains almost negligible with regard to the effective reduction in mass resulting from the recesses operated in the retaining member 32. In other words, whatever the radial extent chosen of the first attachment portion, the sealing of the cooling circuit is improved in the case of a turbine assembly part of the overall desire to reduce mass pushing to initially modify the shape of the retaining member. Also, like the first and second embodiments, the invention advantageously provides in the third and fourth embodiments that the sealing element is installed prestressed in order to make up for an incipient clearance between annular flange 33 and l retaining member 32 as a result of differential expansion.

In all of the embodiments, the sealing device has been described as relating to a single annular element, in other words continuous over 360 °. However, the invention is not limited to this arrangement and provides for the possibility that the sealing device comes from a combination of several sectored sealing elements, in other words each extending over a circumferential sector so that the he set of sealing elements covers 360 ° so as not to jeopardize the overall balance of the turbine. In practice, the choice of such a sealing device resulting from the assembly of several sectored sealing elements is based solely on a simplified manufacture in comparison with the formation of a one-piece 360 ° sealing element. Indeed, in return for easier manufacturability, it is generally found that such an assembly provides lower sealing performance, insofar as slight leaks can occur at the interface between two sectored elements. In this regard, the invention provides, in the context of the third and fourth embodiments of the turbine assembly, to arrange the sectored sealing elements so that they preferentially meet at the level of the solid parts 46 to limit this risk of leakage. It is therefore desired, in the case of the third and fourth embodiments with a sealing device resulting from an assembly of several elements forming a ring sector, that each of these sealing elements extends circumferentially along at least one hollowed out part 47 projecting from the solid parts 46 located on either side.

Finally, in the example of FIGS. 9 to 9B and 10 to 10B relating to the third and fourth embodiments, the retaining member 32 is in the form of a continuous rod along its outer periphery 32a and perforated the along its inner periphery with an alternation of solid parts 46 and hollow parts 47, with as many solid parts as vanes. However, the invention is not limited to this particular architecture, the sealing device finding its application in practice in the case of a retaining member 32 having at least one recessed part. To this end, a sectorized member 32, in other words formed of a plurality of angular segments spaced circumferentially, with the solid parts 46 and hollowed out 47 in this case designating respectively the angular segments and the spaces defined between them, could be retained without departing from the scope of the invention. Whatever the shape of the member 32 adopted, that is to say either of constant circumferential extent over 360 ° as provided in the first and second embodiments or with at least one hollowed out part, the use of an annular sealing element or several elements sectorized and joined end-to-end, each forming a ring sector, remains applicable.

Concretely, the sealing device according to the invention makes it possible to contain the flow of air propagating within the cooling circuit of the disc and, therefore, makes it more efficient for the same quantity of air taken upstream of turbine. With this control of the cooling circuit, it therefore becomes possible to reduce these air samples which do little or nothing to supply energy to the turbomachine, or even cause efficiency losses, without impacting the duration of component life. The sealing device being compatible and effective whatever the shape of the retaining member 32 adopted, the invention thus grants great freedom of design of this member to tend towards an improved sealing system. Finally, the sealing device is adapted to a space-saving environment while adding a small mass by the use of light metal sheets. It should be noted, however, that the invention could provide, if necessary, for the use of another material for the manufacture of the sealing element or elements, since the overall mass of the turbine assembly is not appreciably increased. . Such a material 5 will preferably have a stiffness making it possible to compensate for the effect of the differential expansion by elastic return E of the pre-stressed installed sealing element.

Claims (10)

1. Turbine assembly for an aircraft turbomachine, comprising: - a rotor disc (17) which extends around an axis (AX), the disc (17) being extended axially along the axis (AX) by a flange (36) and carrying a plurality of blades ( 18) radials each comprising a foot (21) engaged in a corresponding axial groove (23) formed at the periphery of the disc (17), with each pair formed by a groove (23) and a foot (21) delimiting between them an axial air flow channel (43); - An annular flange (33), fixed to the flange (36), extending axially towards the disc (17) and which has an annular end (34) extending radially outwards beyond the channel of air flow (43) by delimiting jointly with the flange (36) an air passage (42) communicating with the air flow channel (43); - An axial retaining member (32) of the blades in their corresponding groove (23), which is disposed against the disc (17) by the annular flange (33); this turbine assembly being characterized in that it comprises a sealing device including a sealing element (48, 48 '), this sealing element comprising: a first attachment portion (49, 49 ′) clamped axially between the disc (17) and the axial retaining member (32), and - A sealing portion (51, 51 ') which extends the first attachment portion (49, 49') extending towards the flange (33) to be in contact with this flange (33). 2. The assembly of claim 1, wherein the sealing element (48) is a sheet, with the first attachment portion (49) and the sealing portion (51) which form an obtuse angle in a view. in section along a plane passing through the axis of the disc (AX). 3. The assembly of claim 1, wherein the sealing element (48 ') is a sheet having a U-shaped profile in a sectional view along a plane passing through the axis of the disc (AX), comprising a second attachment portion (52 ') which extends the sealing portion (5Γ) by being clamped between the annular end (34) of the flange (33) and the axial retaining member (32). 4. Assembly according to one of claims 2 and 3, wherein the sheet thickness is 0.1mm to 0.5mm. 5. Assembly according to one of the preceding claims, in which the axial retaining member (32) of the blades is pressed against the disc (17) by the annular flange (33) at the interior periphery of this retaining member. axial (32). 6. Assembly according to one of the preceding claims, in which the device comprises a single annular sealing element, or several sealing elements each forming a ring sector, the sealing elements extending circumferentially by being arranged. end to end. 7. Assembly according to one of the preceding claims, in which: the axial retaining member (32) comprises an alternation between solid parts (46) each extending circumferentially along at least one blade root and pressed towards the disc by the annular end of the flange, and recessed parts (47) each extending in an angular sector delimited between two successive feet (21); and - The first attachment portion (49, 49 ') covers the disc at at least one recessed part (47) located axially opposite the sealing element. 8. Assembly according to one of the preceding claims, wherein the axial retaining member (32) is continuous along its outer periphery (32a). 9. Turbine (8, 9) for an aircraft turbomachine comprising at least one assembly according to one of the preceding claims, the turbine preferably being a low pressure turbine (9). 10. Aircraft turbomachine (1) comprising at least one turbine (8, 9) according to the preceding claim, the turbomachine preferably being a double-body turbomachine.