A turbomachine assembly comprising blades carrying runners and a cable connecting the runners to each other.

Abstract

The invention relates to a rotating turbomachine assembly extending around an axis of rotation, comprising a disk carrying blades (21a, 21b) and intended to be surrounded by a casing through which a flow circulates from upstream to downstream when the turbomachine is in operation, wherein each blade (21a, 21b) extends radially with respect to the axis of rotation from a foot (22a, 22b) by which it is fixed to the disk to a heel (24a, 24b) opposite the foot (22a, 22b), this heel (24a, 24b) comprising a platform (26a, 26b) carrying at least one blade (27a, 27b, 28a, 28b), and wherein: – several blades (27a, 27b, 28a, 28b) comprise at least one through orifice (29a, 29b); – at least one cable (31) passes through openings (29a, 29b) formed in the slots (27a, 27b) of at least two platforms (26a, 26b). Figure for the abbreviation: Figure 3

Description

Title of the invention: Turbomachine assembly comprising blades carrying wipers and a cable connecting the wipers to each other Technical field

[0001] The invention relates to the reduction of vibrations in a turbomachine bladed disc in service. STATE OF THE PRIOR ART

[0002] In such a turbojet 1 shown in [Fig.l], 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.

[0003] The primary flow is then compressed in a first and second compression stage 4 and 6 before arriving in a combustion chamber 7, after which it expands by passing through a set of turbines 8 before being evacuated to the outside, generating thrust. This thrust is generated downstream of the turbojet engine according to the direction of circulation of the flow in the latter. The secondary flow is propelled directly downstream by the fan in a vein delimited by the casing 9 to generate additional thrust.

[0004] In practice, such an engine comprises a rotor rotating around its longitudinal axis AX, and including several discs each carrying at its external periphery a series of blades or vanes, these discs corresponding to the fan, the compressors and the turbines.

[0005] As shown in [Fig.2], such a blade 11a comprises a root 12a by which it is mounted to a disc (not shown), extended by a blade 13a extending in a direction of span EVa radial with respect to the axis of rotation. This blade 13a is terminated by a heel 14a comprising a platform 16a or heel carrying here two wipers 17a, 18a intended to provide sealing functions.

[0006] The blades carried by the same disk have the same morphology, so that the blade 11b circumferentially close to the blade 11a in [Fig.2], comprises the same components identified by the same numerical references but supplemented by the letter “b” instead of the letter “a”.

[0007] The external periphery of a bladed disc is thus delimited by the platforms of the blades that it carries, which extend contiguously circumferentially to each other to jointly delimit a shell.

[0008] In operation, these blades are subjected to high temperatures and central forces significant trifuges, which tend to increase their length according to their span direction. Under these conditions, the circumferentially contiguous platforms, which are joined when the turbomachine is stopped, tend to space themselves circumferentially from each other when the turbomachine is in operation, this spacing or clearance being marked by J in [Fig.2].

[0009] Given the vibrational excitations present in such a turbomachine, this situation can lead to vibrational modes of the blades by which their platforms tend to collide circumferentially with each other, which is likely to degrade them.

[0010] Such vibration modes can appear on rotating blades, i.e. blades carried by disks, but also appear in fixed blades, i.e. blades carried by a fixed element such as a rectifier located for example downstream of a fan or compressor bladed disk to reduce the gyration of the flow having passed through the rotating blades.

[0011] In the case of a rectifier, document FR2978798 teaches providing on the one hand a circumferential cord passing through rings carried by the platforms, and on the other hand that each platform has a protuberance resting on the external face of the neighboring platform.

[0012] In operation, the circumferential friction forces of the cord in the rings oppose the relative movements of the platforms, to reduce the amplitude of their vibration modes. Similarly, the circumferential friction of the protuberances on the external faces slows down the circumferential movements of the platforms relative to each other to reduce the corresponding vibration modes.

[0013] In practice, the implementation of a cord requires the provision of rings or eyelets and the availability of significant space at the external faces of the platforms, which is penalizing in terms of integration to the point that this solution is not compatible with rotating blades.

[0014] The implementation of protuberances generating friction forces requires the establishment of high prestresses during the assembly of the blades, i.e. static constraints complicating both the design and the assembly of these blades.

[0015] Solving this problem for ceramic matrix composite (CMC) blades is more difficult than for metal alloy blades, because the permissible mechanical stresses for CMC blades are lower than those for metal alloy blades.

[0016] In this context, the invention aims to provide a solution for limiting the vibration modes of bladed discs, particularly in the case of blades made of material ceramic matrix composite having a lower permissible prestress than that of metal alloy blades. Statement of the invention

[0017] To this end, the invention relates to a turbomachine bladed assembly extending circumferentially around an axis of rotation, and comprising, in which each blade extends radially to a heel located at a free radial end of the blade, this heel comprising a platform carrying at least one wiper which protrudes radially from the heel, characterized in that:

[0018] - two lips each have at least one through-hole,

[0019] - the bladed assembly comprises at least one cable passing through the two licks for connect them together via their holes.

[0020] With this arrangement, the cable generates friction forces which oppose the relative circumferential movements of the blades in operation, so as to reduce their vibration modes.

[0021] The invention also relates to a bladed assembly thus defined, in which one of the wipers comprises several orifices crossed by the cable.

[0022] The invention also relates to a bladed assembly thus defined, in which each platform carries an upstream lip and a downstream lip, and in which the cable passes through an orifice of the upstream lip and an orifice of the downstream lip.

[0023] The invention also relates to a bladed assembly thus defined, in which the platforms jointly delimit an annular ferrule, and in which the cable extends over 360° around the annular ferrule.

[0024] The invention also relates to a bladed assembly thus defined, in which the ends of the cable are welded or knotted to form a closed loop.

[0025] The invention also relates to a bladed assembly thus defined, in which the cable is a braided cable so as to have a rough surface.

[0026] The invention also relates to a bladed assembly thus defined, in which the cable is formed from a material of the metallic superalloy type based on nickel, cobalt or iron.

[0027] The invention also relates to a bladed assembly thus defined, in which the blades are blades made of ceramic matrix composite material.

[0028] The invention also relates to a turbomachine equipped with a bladed assembly thus defined. Brief description of the drawings

[0029] - [Fig.l] is a longitudinal sectional view of a known turbojet engine;

[0030] - [Fig.2] is a perspective view of two circumferentially adjacent blades adjacent equipping a rotating disk according to an arrangement known to the State of technique;

[0031] - [Fig.3] is a perspective view of two circumferentially adjacent blades adjacent equipping a rotating disk according to the invention;

[0032] - [Fig.4] is a top view of the platforms of two circumferential blades partially adjacent according to the invention;

[0033] - [Fig.5] is a top view of the platforms of four blades in succession adjacent according to the invention;

[0034] - [Fig.6] is a partial view of a turbomachine rotor element equipped of blades according to the invention.

[0035] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0036] The idea behind the invention is to ensure damping of the vibration modes of the blades with a cable connecting together the wipers carried by the platforms of the blades to generate friction forces when these platforms move circumferentially relative to each other. In operation, the friction forces generated oppose the movements of the platforms by dissipating energy to damp the vibration modes.

[0037] In [Fig. 3], a blade 21a has a root 22a by which it is mounted to a disc (not shown), extended by a blade 23a extending in a direction of span EVa radial relative to the axis of rotation of the disc. This blade 23a is terminated by a heel 24a located at its free radial end, this heel comprising a platform 26a carrying here an upstream lip 27a, and a downstream lip 28a intended to provide sealing functions.

[0038] Another blade 21b, circumferentially close to blade 21a in [Fig.3] and which has the same morphology, comprises the same elements designated by the same numerical references but supplemented by the letter “b” instead of the letter “a”.

[0039] These two circumferentially adjacent blades are carried by the same disc (not shown) which rotates around an axis of rotation of the engine when the latter is in operation, and when they are not in operation, the longitudinal edges of the platforms 26a and 26b are joined.

[0040] As visible in [Fig. 3] the upstream wiper 27b of the blade 21b extends circumferentially in the extension of the upstream wiper 27a of the blade 21a. Similarly, the downstream wiper 28b of the blade 21b extends circumferentially in the extension of the downstream wiper 28a of the blade 21a.

[0041] The upstream wipers of the set of blades carried by the disc jointly delimit an upstream crown extending circumferentially around the cylindrical shell delimited by the platforms carrying these wipers. The outer edge of this upstream crown slides along abradable elements (not shown) which are carried by the motor casing, to ensure a seal thanks to which the flow crossing the blades cannot bypass them by passing radially beyond the platforms.

[0042] In the same way, the downstream crown formed by the downstream wipers slides along an abradable element not shown to ensure a seal opposing the passage of flow radially beyond the platforms.

[0043] The upstream crown and the downstream crown 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.

[0044] When the engine they equip is in service, these blades are subjected to high temperatures and to significant centrifugal forces which tend to lengthen these blades in their span direction, and consequently to circumferentially space their platforms from each other.

[0045] Thus, and as shown schematically in [Fig. 3], the longitudinal edges of the platforms 26a and 26b which are contiguous are spaced circumferentially from each other when the engine is in operation, by a clearance marked J.

[0046] This circumferential spacing of the platforms in use contributes to the establishment of a vibration mode by which the platforms move circumferentially relative to each other, their contiguous longitudinal edges then being likely to collide in such a vibration mode.

[0047] According to the invention, several wipers comprise a through orifice, and a cable passes through these orifices, to generate friction when the platforms carrying these wipers move circumferentially relative to each other.

[0048] In [Fig. 3], the lip 27a has a through hole or orifice 29a, and the lip 27b has another through orifice marked by 29b. In addition, a cable marked by 31 passes through these two orifices, constituting, as visible in [Fig. 4], a closed loop extending on either side of each of these lips 27a and 27b.

[0049] In operation, the separation and the bringing together of the two platforms 26a and 26b, under the effect of a vibratory stress, generates friction of the cable 31 at the level of the orifices 29a and 29b which it passes through which oppose these relative movements of the platforms.

[0050] In the example of [Fig.4], the cable 31 forms a loop extending only between the orifices 29a and 29b, but other paths are possible for this cable. For example, all the upstream wipers being provided with an orifice, the cable 31 can pass through each hole, extending alternately along the upstream face and along the downstream face of the upstream crown, so as to describe a zig-zag type pattern, extending over 360° around the axis of rotation.

[0051] The downstream wipers may also include orifices, marked 32a and 32b. in [Fig.5], in which there is shown, in addition to platforms 26a and 26b, another platform 26c carrying upstream 27c and downstream 28c lips, and another platform 26d carrying upstream 27d and downstream 28d lips.

[0052] In this other configuration, the cable 31 forms a loop passing through the orifices 29a-29d and 32a-32d of the different wipers, while constituting a loop which extends from the upstream crown to the downstream crown.

[0053] More particularly, the cable 31 extends on either side of the upstream crown, passing through its orifices 29b and 29c, it extends on either side of the downstream crown, passing through its orifices 32b and 32c, and it successively passes through the orifices 29a and 32a as well as the orifices 29d and 32d, extending parallel to the axis AX, so as to constitute a closed loop.

[0054] Here again, other arrangements are possible, such as for example a first cable passing through all the orifices of the upstream crown to form a zigzag type pattern there, and another cable passing through all the orifices of the downstream crown to form another zigzag pattern there.

[0055] It is also possible to provide several orifices per lip, so as to increase the contact surface between the cable and the orifices so as to increase the friction forces generated when the assembly is in operation.

[0056] More generally, the cable 31 is not taut: on the contrary, it is loose when the turbomachine is stopped, so as not to be subjected to excessive internal stresses when the turbomachine is in operation.

[0057] The centrifugal force that the cable undergoes when the turbomachine is put into service ensures that the cable is in effective contact with the orifices that it passes through when the turbomachine is in service, so as to generate friction forces under the effect of the relative circumferential movements of the platforms.

[0058] As regards the assembly, the cable is advantageously put in place after assembly of the blades on the disc which carries them, by being inserted into the corresponding orifices, the ends of the cable being knotted or welded to each other so as to constitute a closed ball.

[0059] To increase the friction forces that it generates, the cable advantageously has a rough texture like that of a braid, which can be made of a metallic superalloy based on nickel, cobalt or iron. The objective being to have a high coefficient of friction between the cable and each hole that it passes through, this can be obtained by a braided cable or by any other means to increase the roughness, such as for example sandblasting.

[0060] A bladed assembly comprising blades according to the invention may belong to a turbomachine rotor element, such as the rotor disk DR, a part of which is shown in [Fig. 6]. The blades 21a, 21b may then be mounted by their roots 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.

[0061] Generally speaking, the invention has been presented for rotary blades comprising a platform and at least one wiper made of CMC type material, but the invention also applies to blades made of metal alloy.

Claims

Claims

1. A turbomachine bladed assembly extending circumferentially around an axis of rotation, and comprising blades (21a, 21b), in which each blade (21a, 21b) extends radially to a heel (24a, 24b) located at a free radial end of the blade (21a, 21b), this heel (24a, 24b) comprising a platform (26a-26d) carrying at least one upstream wiper (27a-27d) and one downstream wiper (28a-28d) which protrude radially from the heel (24a, 24b), characterized in that: - the upstream wipers (27a-27d) and the downstream wipers (28a-28d) carried by at least two circumferentially adjacent platforms (26a-26d) each comprise an orifice (29a-29d, 32a-32d) passing through, - the bladed assembly comprises at least one cable (31) passing through the orifices (29a-29d, 32a-32d) of the upstream wipers (27a-27d) and the downstream wipers (28a-28d) carried by these circumferentially adjacent platforms (26a-26d) to connect them together.

2. A bladed assembly according to claim 1, wherein one of the wipers (27a-27d, 28a-28d) comprises several orifices through which the cable (31) passes.

3. A bladed assembly according to claim 1 or 2, wherein the circumferentially adjacent platforms (26a-26d) jointly define an annular ferrule, and wherein the cable (31) extends 360° around the annular ferrule.

4. A bladed assembly according to one of claims 1 to 3, wherein the ends of the cable (31) are welded or knotted together to form a closed loop.

5. A bladed assembly according to one of claims 1 to 4, wherein the cable (31) is a braided cable so as to have a rough surface.

6. A bladed assembly according to one of claims 1 to 5, wherein the cable is formed from a metal superalloy type material based on nickel or cobalt or iron.

7. A bladed assembly according to one of claims 1 to 6, in which the blades (21a, 21b) are blades made of ceramic matrix composite material.

8. Turbomachine equipped with a bladed assembly according to one of claims 1 to 7.

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