FR3137124A1 - Turbomachine assembly comprising blades carrying liplets whose ends overlap each other in the circumferential direction - Google Patents

Abstract

The subject of the invention is a rotary assembly of a turbomachine rotating around an axis (AX), comprising a disc carrying blades (21b, 21c) and being intended to be surrounded by a casing crossed by a flow circulating from upstream to downstream, in which each blade (21b, 21c) extends radially from a foot (22b, 22c) to a heel (24b, 24c) comprising a platform (26b, 26c) carrying at least one lip (27a, 27b ), characterized in that: – it comprises an alternation of blades (21c) prestressed towards the upstream and blades (21b) prestressed towards the downstream, each blade prestressed towards the upstream (21c) having its heel ( 24c) tending to shift upstream, each blade prestressed downstream (21b) having its heel (24b) tending to shift downstream; – the pairs of adjacent blades have blades (27b, 27c) whose ends (27b1, 27b2, 27c1, 27c2) overlap while being pressed axially by the prestressing of the blades. Figure for abstract: Figure 3

Description

Turbomachine assembly comprising blades carrying liplets whose ends overlap each other in the circumferential direction

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

STATE OF PRIOR ART

In such 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 fixed 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 here carrying two lips 17a, 18a intended to ensure 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 joined in the circumferential direction when the turbomachine is stopped, tend to space circumferentially from each other when the turbomachine is in service, this spacing or clearance being identified by J on there . 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 platform supports, which allows these vibration modes to be damped by friction.

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 circumferentially around an axis of rotation and comprising blades, in which each blade extends radially relative to the axis of rotation up to a heel located at a free end of the blade, this heel comprising a platform carrying at least one lip which extends radially protruding from the platform, characterized in that two circumferentially adjacent blades have lips whose ends extend circumferentially so as to overlap in the direction of the axis of rotation while being in axial contact with each other.

With this arrangement, the blades only have to be prestressed in the axial direction, which significantly simplifies the implementation of a vibration mode damping solution.

The invention also relates to a bladed assembly thus defined, comprising an alternation of blades prestressed towards the upstream and blades prestressed towards the downstream, each blade prestressed towards the upstream having its heel tending to shift towards the upstream , each blade prestressed towards the downstream having its heel tending to shift towards the downstream.

The invention also relates to a bladed assembly thus defined, in which each blade carries an upstream lip and a downstream lip which protrude radially from the platform, and in which the circumferential ends of the upstream lip of two circumferentially adjacent blades extend circumferentially so to overlap in the direction of the axis of rotation.

The invention also relates to a bladed assembly thus defined, in which each blade carries an upstream lip and a downstream lip, and in which the ends of downstream lip of two circumferentially adjacent blades extend circumferentially so as to overlap in the direction of the axis of rotation.

The invention also relates to a bladed assembly thus defined, in which at least one lip has circumferential ends which are offset axially relative to the body of this lip.

The invention also relates to a bladed assembly thus defined, comprising an alternation of blades, each blade comprising one or more blades whose ends extend so as to protrude circumferentially from the platform which carries them, and one or more blades whose ends ends extend without protruding circumferentially from the platform which carries them.

The invention also relates to a bladed assembly thus defined, in which the blades are made of ceramic matrix composite material.

The invention also relates to a bladed assembly thus defined, in which the blades are prestressed by offset of their feet relative to the disc which carries them, in the direction close to the axis of rotation.

The invention also relates to a bladed assembly thus defined, in which the blades are prestressed by being curved upstream or downstream when viewed in a plane containing the axis of rotation.

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 two circumferentially adjacent blades fitted to a rotating disk according to the invention;

- There is a top view of the platforms of four circumferentially adjacent blades in accordance with a first embodiment of the invention;

- There is a side view of a first example of a blade prestressed upstream;

- There is a side view of a second example of a pre-stressed upstream blade;

- There is a top view of the platforms of four circumferentially adjacent blades in accordance with a second embodiment of the invention;

- There is a top view of the platforms of four circumferentially adjacent blades in accordance with a third embodiment of the invention;

- 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 ensure vibration damping by providing ends of wipers which overlap while being axially supported on each other to generate frictional forces when the platforms carrying these wipers move circumferentially relative to each other. In this context, the blades are pre-stressed alternately upstream and downstream, so as to ensure that the lip ends are axially pressed on top of each other.

On the , a blade 21b comprises a foot 22b by which it is fixed to a disk (not shown), extended by a blade 23b extending in a direction of span EVb radial with respect to the axis of rotation of the disk. This blade 23b is terminated by a heel 24b comprising a platform 26b or heel here carrying an upstream lip 27b, and a downstream lip 28b intended to ensure sealing functions. This platform 26b is delimited circumferentially by two longitudinal edges 29b and 31b.

Another dawn 21c, close to dawn 21b on the and which has the same morphology, includes the same elements designated by the same numerical references but ending with the letter “c” instead of the letter “b”. These two blades are carried by the same disc, not shown, which rotates around an axis of rotation when the engine is in service.

As visible on the the downstream lip 28c of the blade 21c extends circumferentially in the extension of the downstream lip 28b of the blade 21b. Similarly, the upstream lip 27c of the blade 21c extends circumferentially essentially in the extension of the upstream lip 27b of the blade 21b.

The upstream lip of all the blades carried by the disc jointly delimit an upstream lip extending circumferentially around the cylindrical ring delimited by the platforms. The outer edge of this upstream lip slides along abradable elements not shown carried by a casing, to ensure a seal so that the flow crossing the blades does not bypass them by passing beyond the platforms.

In the same way, the downstream wiper constituted by the downstream wipers slides along an abradable element not shown to ensure a seal opposing the passage of flow radially beyond the platforms. The upstream lip and the downstream lip are spaced from each other along the axis of rotation of the motor by a distance less than the length of the platforms along this axis.

As visible in Figures 3 and 4, the upstream lips 27b and 27c have ends which overlap circumferentially while bearing in the axial direction corresponding to the axis of rotation AX of the motor against each other.

The lip 27b is a straight lip which extends circumferentially from a first circumferential end 27b1 to a second end 27b2. This lip 27b is straight, that is to say it extends substantially along the same plane normal to the axis of rotation AX.

The wiper 27c is a wiper with offset ends which extends circumferentially from a first end 27c1 to a second end 27c2, but its first end 27c1 is offset axially downstream relative to the body of the wiper 27c, and it protrudes circumferentially beyond the longitudinal edge 29c of the platform. The second end 27c2 is also offset axially downstream relative to the body of the lip 27c and it protrudes beyond the longitudinal edge 31c. It is also possible to provide a configuration in which the ends are offset axially upstream instead of being offset downstream.

As visible in Figures 3 and 4, thanks to the offset of the first end 27c1 and its protrusion from the longitudinal edge, this first end 27c1 circumferentially overlaps or overlaps the second end 27b2, to be in axial support against it in the direction AX.

Generally speaking, the blades with straight blades and offset ends are mounted circumferentially alternately around the disc which carries them, such that all the ends of the upstream blades overlap.

According to this alternation which appears more clearly on the , a second end 27a2 of a wiper 27a with offset ends carried by a platform 26a of a blade 21a circumferentially adjacent to the blade 21b, axially overlaps the first end 27b1 of the straight wiper 27b carried by the platform 26b.

The second end 27b2 of the right upstream lip 27b is overlapped axially by the first end 27c1 of the lip 27c having offset ends. The second offset circumferential end 27c2 of the lip 27c axially overlaps a first end 27d1 of a straight upstream lip 27d carried by a platform 26d of another blade 21d which is circumferentially adjacent to the blade 21c.

Complementary to the axial overlap of all the ends of the upstream lip, the blades 21b and 21d with straight blades and the blades 21a and 21c with blades having offset ends are prestressed in opposite directions in the axial direction, as indicated by the arrows on there . These prestresses make it possible to maintain the ends of the wipers which overlap axially in support of each other in the axial direction AX. In the case where the ends of the tongues are offset upstream instead of being offset downstream, the directions of the prestressing must be reversed to ensure support for these ends.

More particularly, the blades 21b and 21d are pre-stressed to continually tend to shift their platforms downstream, while the blades 21a and 21c are pre-stressed to continually tend to shift their platforms upstream.

The prestressing of a blade towards the upstream can be ensured by shifting its root upstream along the axis AX in relation to the other blades, as illustrated schematically on the . Analogously, the prestressing of a blade towards the downstream can be obtained by shifting its foot towards the downstream in relation to the other blades.

In practice, the offset of a blade along the axis AX can correspond to an offset in a direction slightly inclined relative to that of the axis AX, this direction corresponding to the axis of engagement of the root. blade in the disk, called axis or broaching direction which can be slightly oblique to the axis AX.

It is also possible to provide, on the one hand, blades slightly curved towards the upstream so that they are pre-stressed towards the upstream, as illustrated in the example of the , and on the other hand blades slightly prestressed towards the downstream so that they are prestressed towards the downstream.

Thus, different relatively simple solutions exist to obtain different prestresses or compensations depending on the axial direction on the blades, these being arranged alternately around the disc to be prestressed alternately upstream and downstream.

The alternation of preload can be obtained by providing an alternation of blades without compensation and of blades having compensation towards the upstream or of blades having compensation towards the downstream. When the assembly is assembled, the support exerted by the uncompensated blades on the compensated blades then necessarily generates an alternation of prestressing upstream and downstream.

Under these conditions, the ends of the wipers in contact and resting on each other make it possible to dampen the vibration modes. More particularly, when the platforms of two circumferentially adjacent blades approach and move away circumferentially from each other under the effect of a vibration mode, the axial support of the ends of their lip generate friction forces which oppose these movements, to dampen the vibration mode, by dissipation of energy.

This damping also works in the case of vibration mode generating differential movements of the platforms according to their radial directions (span directions). Furthermore, in the case of a vibration mode presenting axial displacements, the device can act as a vibration limiter, except in the case where the blades vibrate in phase.

As will be understood, the degree of prestressing of the blades upstream and downstream is dimensioned to generate a pressing force at the level of the contacts between the ends of the blades making it possible to dissipate the energy resulting from the vibration modes.

In the example of the , the upstream seals all have overlapping ends, while the downstream seals are straight seals whose ends do not extend beyond the longitudinal edges so that these ends do not overlap.

It is also possible, as illustrated in the , to provide, conversely, straight lips that do not overlap for the upstream lip, and lips whose ends all overlap for the downstream lip. In this case, and as illustrated in the , the lips 28b and 28d are straight and have straight ends 28b1, 28b2 and 28d1 not exceeding the longitudinal edges, while the lips 28a and 28c have offset ends 28a2, 28c1 and 28c2 which protrude from the longitudinal edges, to cover circumferentially the ends 28b1, 28b2 and 28d1.

It is still possible, as illustrated in the to provide wipers having ends which overlap circumferentially for the entire upstream wiper and also for the entire downstream wiper.

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 21b, 21c can then be mounted by their feet in corresponding cells of this disc DR by constituting a crown of blades 21b, 21c which surround the disc DR while being carried by it.

Generally speaking, the invention was presented for rotating blades comprising a platform and at least one lip manufactured from CMC type material, but the invention also applies to blades made of a metal alloy.

Claims (10)

Bladed turbomachine assembly extending circumferentially around an axis of rotation (AX) and comprising blades (21a-21d), in which each blade (21a-21d) extends radially relative to the axis of rotation ( AX) to a heel (24b, 24c) located at a free end of the blade (21a-21d), this heel (24b, 24c) comprising a platform (26a-26d) carrying at least one lip (27a- 27d, 28a-28d) which extends radially protruding from the platform (26a-26d), characterized in that two circumferentially adjacent blades have lips (27a-27d) whose ends (27a1-27d1, 27a2-27d2) extend circumferentially so as to overlap in the direction of the axis of rotation (AX) while being in axial contact with each other. Bladed assembly according to claim 1, comprising an alternation of blades (21a, 21c) prestressed upstream and blades (21b, 21d) prestressed downstream, each blade prestressed upstream (21a, 21c) having its heel (24c) tending to shift towards the upstream, each vane prestressed towards the downstream (21b, 21d) having its heel (24b) tending to shift towards the downstream. Bladed assembly according to claim 1 or 2, in which each blade (21a-21d) carries an upstream lip (27a-27d) and a downstream lip (28a-28d) which project radially from the platform, and in which the circumferential ends ( 27a1-27d1, 27a2-27d2) of upstream lips (27a-27d) of two circumferentially adjacent blades extend circumferentially so as to overlap in the direction of the axis of rotation. Bladed assembly according to one of claims 1 to 3, in which each blade (21a-21d) carries an upstream lip (27a-27d) and a downstream lip (28a-28d), and in which the ends (28a1-28d1, 28a2-28d2) of downstream lips (28a-28d) of two circumferentially adjacent blades extend circumferentially so as to overlap in the direction of the axis of rotation. Bladed assembly according to claim 3 or 4, in which at least one lip (27a-27d, 28a-28d) has circumferential ends (27a1-27d1, 27a2-27d2, 28a1-28d1, 28a2-28d2) which are offset axially by relation to the body of this lick (27a-27d, 28a-28d). Bladed assembly according to one of claims 1 to 5, comprising an alternation of blades (21a, 21c), each blade comprising one or more lip(s) (27a, 27c) whose ends (27a2, 27c1, 27c2) extend from so as to protrude circumferentially from the platform (26a, 26c) which carries them, and one or more pads (27b, 27d) whose ends (27b1, 27b2, 27d1, 27d2) extend without protruding circumferentially from the platform (26b, 26d) who wear them. Bladed assembly according to one of claims 1 to 6, in which the blades (21a-21d) are made of ceramic matrix composite material. Bladed assembly according to one of claims 1 to 7, in which the blades (21a-21d) are prestressed by offset of their feet (22b, 22c) relative to the disc which carries them, in the direction of the axis of rotation (AX). Bladed assembly according to one of claims 1 to 8, in which the blades (21a-21d) are prestressed by being curved upstream or downstream when viewed in a plane containing the axis of rotation (AX). Turbomachine comprising a bladed assembly according to one of claims 1 to 9.