FR3137125A1 - Bladed turbomachine assembly comprising blades joined together in pairs at their platforms - Google Patents

Abstract

The invention relates to a rotating turbomachine assembly extending around an axis of rotation (AX), comprising a disk carrying blades (21a, 21b), in which each blade (21a, 21b) extends in one direction. of radial span, from a foot (22a) by which it is secured to the disc to a heel (27a) opposite the foot (22a), this heel (27a) comprising a platform (28a, 28b), two platforms circumferentially adjacent ones having contiguous edges (32a, 33b) facing each other. This assembly comprises at least one clamping element (35) enclosing edge to edge two circumferentially contiguous platforms (28a, 28b), each of the two platforms (28a, 28b) comprising a hole passing through it from side to side, and the clamping element clamp (35) passes through these two holes to exert between these two platforms (28a, 28b) a tension force oriented circumferentially relative to the axis of rotation (AX). Figure for abstract: Figure 3

Description

Bladed turbomachine assembly comprising blades joined together in pairs at the level of their platforms

The invention relates to the reduction of vibrations in a bladed disk of a turbomachine in service.

STATE OF PRIOR ART

In a turbomachine such as a turbojet 1 shown in , the outside air is admitted into an inlet sleeve 2 to pass through a fan 3 comprising a series of rotating blades before splitting into a central primary flow and a secondary flow surrounding the primary flow.

The primary flow is then compressed in a first and a second compression stages 4 and 5 before arriving in a combustion chamber 6, after which it expands passing through a set of turbines 7, 8 before being evacuated towards the back by generating thrust. The secondary flow is propelled directly backwards by the fan in a vein delimited by the casing 9 to generate additional thrust.

In practice, such an engine comprises a rotor rotating around its longitudinal axis AX, and including several disks each carrying at its external periphery a series of blades or blades, these disks being able to drive the fan, the compressor part or the turbine part .

As shown on the , such a blade 11a comprises a foot 12a by which it is mounted to a disk (not shown), extended by a blade 13a extending in a direction of span EVa radial to the axis of rotation. This blade 13a is terminated by a heel 14a comprising a platform 16a or heel provided with two lips 17a, 18a extending radially beyond the upper face of this platform, and which are intended to provide sealing functions.

The blades carried by the same disc have the same morphology, so that the blade 11b neighboring the blade 11a on the , includes the same components identified by the same numerical references but supplemented by the letter “b” instead of the letter “a”.

The external periphery of a bladed disk is thus delimited by the platforms of the blades which it carries, which extend contiguous to each other to jointly delimit a substantially cylindrical peripheral band.

In operation, these blades undergo high temperatures and significant centrifugal forces, which tend to increase their length depending on their span direction. Under these conditions, the contiguous platforms, which are contiguous when the turbomachine is stopped, tend to space themselves circumferentially from each other when the turbomachine is in service, this spacing or clearance being identified by J on the . A circumferential expansion of the platforms also takes place, which limits the game in question but without canceling it.

Given the vibration excitations present in such a turbomachine, this situation can lead to vibration modes of the blades by which their platforms tend to collide circumferentially with each other, which is likely to damage them.

Such vibration modes can appear on rotating blades, that is to say carried by discs, but also appear in fixed blades, that is to say carried by a fixed element such as a rectifier located for example in downstream of a bladed fan or compressor disk to reduce the gyration of the flow having passed through the rotating blades.

A solution to damp vibration modes is to pre-stress each blade in torsion when they are mounted on the disk. In this case, the platforms tend to rotate around their span axes, so that the edges of the platforms of two adjacent blades remain supported against each other despite the effects of centrifugal forces and thermal expansion.

In operation, the vibration modes of the blades generate friction at the level of the platform supports, which makes it possible to dampen these vibration modes by friction, according to a so-called friction contact solution.

This solution nevertheless requires mechanically prestressing the blades during their assembly, which leads to high levels of mechanical stress which may not be compatible in the case of blades made of ceramic matrix composite (CMC) material.

In this context, the object of the invention is to provide a solution for limiting the vibration modes of bladed disks, in particular for the case of blades made of composite material with a ceramic matrix having a lower admissible prestress than that of blades made of metal alloy. .

For this purpose, the subject of the invention is a bladed turbomachine assembly extending around an axis of rotation, and comprising at least two circumferentially contiguous blades, in which each blade extends in a radially oriented span direction. relative to the axis of rotation, from a foot by which it is secured to the disc to a heel located at a free radial end of the blade, this heel comprising a platform, two circumferentially adjacent platforms having circumferentially contiguous edges facing each other, characterized in that it comprises at least one clamping element enclosing edge to edge two circumferentially contiguous blade platforms, in that each of the two platforms has a hole passing through it from side to side part, and in that the clamping element passes through these two holes to exert between these two platforms a tension force oriented circumferentially relative to the axis of rotation.

With this solution, it is not necessary to pre-stress the blades during assembly, so that it is possible to ensure vibration damping without generating high mechanical stresses in the blades.

The invention also relates to a bladed assembly thus defined, in which each platform extends parallel to the axis of rotation, each platform comprising a hole passing through it from side to side, and in which the clamping element passes through from side to side. on each platform.

The invention also relates to a bladed assembly thus defined, in which each platform comprises at least one lip, each lip comprising a hole passing through it right through, and in which the clamping element passes through two wipers right through.

The invention also relates to a bladed assembly thus defined, in which the holes through which the clamping element passes are slots inclined to move away from each other away from the axis of rotation.

The invention also relates to a bladed assembly thus defined, in which the clamping element is a cable whose ends are connected to each other to form a loop.

The invention also relates to a bladed assembly thus defined, comprising a weight carried by the cable to increase its tension by centrifugal effect when the engine is in service.

The invention also relates to a bladed assembly thus defined, in which the clamping element is a clip.

The invention also relates to a bladed assembly thus defined, comprising several clamping elements enclosing two circumferentially contiguous blades.

The invention also relates to a bladed assembly thus defined, in which two blades having their plates enclosed by a clamping element are blades made of composite material with a ceramic matrix.

The invention also relates to a turbomachine comprising an assembly thus defined.

- There is a longitudinal sectional view of a known turbojet;

- There is a perspective view of two circumferentially adjacent blades equipping a rotating disk according to an arrangement known from the state of the art;

- There is a perspective view of a pair of contiguous blades secured by their platforms in accordance with the invention;

- There is a local cross-sectional view of the heels of two blades secured to each other in accordance with the invention;

- There is a local cross-sectional view of the heels of two blades secured to each other with a cable provided with an unbalance;

- There is a schematic view representing the bending of two blades secured to each other under the effect of centrifugal forces and thermal expansion;

- There is a local cross-sectional view of the heels of two blades secured to each other with a first type of clip;

- There is a local cross-sectional view of the heels of two blades secured to each other with a second type of clip;

- There is a perspective view of a pair of contiguous blades secured by their platforms according to a first variant of the invention;

- There is a perspective view of a pair of contiguous blades secured by their platforms according to a second variant of the invention;

- There is a local cross-sectional view of the heels of two blades secured to each other by a clamping element passing through holes having divergent slot shapes;

- There is a perspective view of a pair of contiguous blades secured by their platforms according to a third variant of the invention;

- There is a perspective view of a pair of contiguous blades having angular contact surfaces at their platforms;

- There is a schematic view representing the bending of two blades secured to the same central blade under the effect of centrifugal forces and thermal expansion;

- There is a partial view of a turbomachine rotor element equipped with blades according to the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

The idea underlying the invention is to force the circumferentially contiguous blade platforms to be in contact to generate damping friction. This is ensured only at the level of pairs of circumferentially contiguous blades by securing their platforms with a clip or the like.

Maintaining contact while the engine is running, despite the centrifugal efforts tending to move the platforms apart, is made possible by the bending of the blades towards each other.

The stiffness of two blades thus joined by their platforms is increased to become that of a double blade, which makes it possible to escape vibrational resonances.

On the , a blade 21a comprises a foot 22a by which it is fixed to a disk (not shown), extended by a blade 23a extending in a direction of span EVa radial with respect to the axis of rotation AX of the disk which door. This blade 23a has an intrados 24a and an extrados not visible in the figure. It is terminated by a heel 27a located at a free radial end of the blade, this heel comprising a platform 28a which is here a plate 29a carrying an upstream lip portion 30a, and a downstream lip portion 31a intended to provide functions sealing.

This blade 21a is contiguous to a blade 21b having a similar geometry, which is why this blade 21b comprises, as visible on the the same parts which are identified by the same numerical references but completed by the letter “b” instead of the letter “a”.

When the blades 21a and 21b are carried by a disc being close to each other, their platforms have contiguous longitudinal edges 32a, 33b facing each other.

In the example of the , the edges 32a and 33b are held in support against each other in the circumferential direction thanks to a clamping element 35 which can be a cable 34 appearing more clearly on the , which forms a loop crossing the two platforms to enclose their edges 32a and 33b, one pressing against the other. This cable constitutes a loop by having its two ends rigidly secured to each other, for example by crimping.

More particularly, the platform 28a comprises a hole 36a which is oriented radially, that is to say perpendicular to the direction AX, to pass through the plate 29a from one side to the other, this hole being located in the vicinity of the edge 32a. In a similar manner, the platform 28b has a hole 36b passing radially through its plate 29b in the vicinity of its edge 33b. These holes pass radially through the plates 29a, 29b of these platforms, these plates having the general shapes of plates oriented parallel to the axis of rotation, that is to say according to planes normal to a direction perpendicular to the axis of rotation. rotation.

The cable 34 constitutes a closed loop which runs along the external and internal faces of the platforms 28a and 28b while passing through their holes 36a, 36b. This cable 34 can be installed by being passed through the holes 36a, 36b, then cut to the correct length and tightened so as to press the edges 32a and 33b against each other before fixing its ends together. to the other for example by crimping or the like.

Advantageously, the loop portion of the cable which runs along the radially external face of the platforms is equipped with a weight forming an unbalance, which makes it possible to tension the cable under the effect of centrifugal forces when the motor is in service, as illustrated in the figure. where this weight or weight is marked by 37.

In operation, the blade platforms tend to deviate from the axis of rotation AX due to centrifugal forces. As a result, the diameter delimited by the platforms tends to increase when the engine is in service, so that the platforms tend to move away from each other.

Thanks to the invention, and as illustrated in the , two blades of the same pair which are secured by their heels are forced to flex so that their platforms remain contiguous and resting on one another taking into account the attachment formed by the cable 34 which encloses them. The tension of the cable, which is if necessary increased by the centrifugal forces it undergoes, thus ensures that the platforms remain in contact to absorb vibrations, without it being necessary to pre-stress them during their assembly on the disc which supports them. door.

Thus, on the , when the engine is in operation, the spacing of the blades linked to the enlargement of the disc caused by the centrifugal effect and thermal expansion, combined with the enclosing of the plates 29a and 29b edge to edge by the cable 34 tend to bend the blade 23a on the side of its upper surface towards the blade 21b, while the blade 23b bends on the side of its lower surface towards the blade 21a. As we understand from the sight of the , these flexions are exerted in a plane normal to the axis of rotation AX.

In the example of Figures 3 to 5, the clamping element 35 ensuring the joining of the two platforms 28a, 28b is a cable 34 passing through the holes 36a and 36b formed in these platforms which they pass right through. But other solutions can be considered, as in the variant of the where the joining of the two platforms is ensured by a clip 38.

As visible on the , this clip 38 comprises a substantially rectilinear body 39 which runs along the radially external face of the platforms 28a and 28b, and which is extended at each of its ends by two branches 41 extending perpendicular to the body 39 and parallel to one other to engage respectively in holes 36a and 36b. The clip 38 can also be mounted in the other direction with the body 39 running along the radially internal face of the platforms 28a and 28b. This staple can be manufactured by cutting and/or folding a sheet metal, or by forming a rod. The material of the clip is designed to withstand high temperatures, this material may for example be a super-alloy.

Each branch is terminated by a tab 42, each tab 42 extending at right angles to the branch which it extends so as to be folded down along the internal face of the platform which it crosses. These tabs 42 thus ensure that the clip 38 is not extracted under the effect of centrifugal forces when the engine is in service.

The assembly of this clip consists for example of engaging its branches 41 in the holes 36a and 36b, before folding its legs 42 by plastic deformation.

To increase the intensity of the pressing force exerted by the clip on the platforms and which tends to press their edges circumferentially against each other, the body 39 of the clip can be in the form of a elastic element such as a spring which is continually stressed in tension when the clip is in place, as in the example of the . The clip is then advantageously obtained by forming a rod to constitute the spring at its body, and to also constitute its branches.

In the example of the , a single clamping element 35 has been provided to secure two platforms, but it is possible to provide several clamping elements 35 to secure two platforms, as in the example of the where two clamping elements 35 are provided.

One of these clamping elements 35 is located upstream of the upstream lips 30a and 30b, and the other is located downstream of the downstream lips 31a and 31b. These clamping elements 35 can be either cables or clips.

Furthermore, the clamping elements 35 used can pass through holes in the body of the platform as in Figures 3 to 5 and 7 to 9, but these clamping elements can also be arranged to pass through the lip portions as in the example of the . In this case, two elements 35 are advantageously provided, one enclosing the downstream lips 31a and 31b, and the other enclosing the upstream lips 30a, 30b.

In this case, the elements 35, which can be clips or cables, can be engaged in holes that are not circular as in the previous examples, but in holes having the shape of slots or notches that are radially divergent from one another. to the other. In this case which is illustrated on the , the holes 36a and 36b which are formed in the lips 31a and 31b have the shape of slots which are inclined so as to move away from each other in the circumferential direction when moving away from the axis of rotation.

Consequently, due to the fact that the centrifugal forces applied to the elements 35 tend to move them away from the axis of rotation, the rotation of the motor tends to put these elements 35 in tension, to increase the gripping force that they exert on the platforms.

In the examples which have been illustrated in Figures 3 to 11, the clamping elements 35 are engaged in holes formed in the vicinity of the edges 32a and 33b which they enclose, but these clamping elements 35 can also be engaged in holes through-holes 36a and 36b formed at a distance from the edges 32a and 33b which they enclose, as illustrated in the .

In the case of the , these holes 36a and 36b are in the form of notches or notches formed at the edges opposite the edges 32a and 33b of the platforms and opening circumferentially into these opposite edges. The clamping element here is a clip 38 mounted in the same way as in the example of the , but whose body extends over the entire length of the platforms 28a and 28b in the circumferential direction.

In the examples of Figures 3 to 12, the edges 32a and 33b enclosed by the clamping element(s) 35 are shown as being substantially rectilinear and parallel to the axis of rotation. These edges can also have complementary angular shapes as in the example of the .

These complementary angular shapes make it possible in particular to generate contact forces which improve the efficiency of dissipation of vibrational energy, and thereby the amplitude of vibrations.

Generally speaking, the object of the invention is to join groups of circumferentially contiguous blades by their platforms so as to constitute sectors of blades mechanically secured to each other at the level of their heels. Such a sector of blades thus has greater rigidity, which makes it possible to limit the amplitude of the vibration modes that they undergo.

The heels of two consecutive blade sectors are thus mechanically dependent.

On the a blade sector is shown comprising three blades 21a, 21b, 21c secured together at their heels by two clamping elements not shown.

According to this arrangement, the two blades 21a and 21b are located on either side of the central blade 21c which is of the same type as the other two. In operation, taking into account the symmetry of this arrangement with respect to the central blade 21c, this central blade does not bend when the engine is in service, and the blades 21a and 21b bend in the same way as in the example of there .

The number of blades in a sector can be two, three or more, depending on the sizing and operating requirements of the engine.

A bladed assembly comprising blades according to the invention may belong to a turbomachine rotor element, such as the DR rotor disk, part of which is shown on the . The blades 21a, 21b can then be mounted by their feet in corresponding cells of this disc DR by constituting a crown of blades 21a, 21b which surround the disc DR while being carried by it.

The invention makes it possible to reduce the deformation of the blades under the effect of vibrations, that is to say to reduce the amplitude of the vibrations to which they are subjected. Dissipation of vibrations is ensured by the friction of the blades between them, the contact forces of which are controlled thanks to the clamping elements which grip their platforms.

It applies to any type of blade, fixed or mobile, compressor, turbine, which may be made of alloy, composite material such as ceramic matrix composite (CMC) or other.

The advantage of the invention lies in the fact that it does not require pre-stressing the blades during assembly, which makes it possible to reduce the mechanical stresses in the blades in operation. Under these conditions, the invention is advantageous for blades made of composite material with a ceramic matrix, given that this material supports lower mechanical stresses than other materials.

Claims (10)

Bladed turbomachine assembly extending around an axis of rotation (AX) and comprising at least two circumferentially contiguous blades (21a, 21b), in which each blade (21a, 21b) extends in a span direction oriented radially relative to the axis of rotation (AX), up to a heel (27a) located at a free radial end of the blade (21a, 21b), this heel (27a) comprising a platform (28a, 28b) , two circumferentially adjacent platforms having contiguous edges (32a, 33b) circumferentially facing each other, characterized in that it comprises at least one clamping element (35) enclosing edge to edge two platforms (28a, 28b) of circumferentially contiguous blades (21a, 21b), in that each of the two platforms (28a, 28b) has a hole (36a, 36b) passing right through it, and in that the clamping element ( 35) passes through these two holes (36a, 36b) being arranged to exert between these two platforms (28a, 28b) a tension force oriented circumferentially relative to the axis of rotation (AX). Bladed assembly according to claim 1, in which each platform (28a, 28b) extends parallel to the axis of rotation (AX), each platform (28a, 28b) comprising a hole (36a, 36b) passing right through it. part, and in which the clamping element (35) passes right through each platform (28a, 28b). Bladed assembly according to claim 1, in which each platform (28a, 28b) comprises at least one lip (30a, 30b, 31a, 31b), each lip comprising a hole (36a, 36b) passing right through it, and in which the clamping element (35) passes right through two wipers (30a, 30b, 31a, 31b). Bladed assembly according to claim 3, in which the holes (36a, 36b) through which the clamping element (35) passes are inclined slots which move away from each other moving away from the axis of rotation (AX). Bladed assembly according to one of claims 1 to 4, in which the clamping element (35) is a cable (34) whose ends are connected to each other to form a loop. Bladed assembly according to claim 5, comprising a weight (37) carried by the cable (34) to increase its tension by centrifugal effect when the engine is in service. Bladed assembly according to one of claims 1 to 6, in which the clamping element (35) is a clip (38). Bladed assembly according to one of claims 1 to 7, comprising several clamping elements (35) enclosing two circumferentially contiguous blades (21a, 21b). Bladed assembly according to one of claims 1 to 8, in which two blades (21a, 21b) having their plates (29a, 29b) enclosed by a clamping element (35) are blades made of composite material with a ceramic matrix. Turbomachine comprising an assembly according to one of claims 1 to 9.