Turbomachine assembly comprising platforms having edges provided with complementary protrusions and notches and associated turbomachine

Abstract

The invention relates to a bladed turbomachine assembly extending around an axis (AX), this turbomachine comprising a disk carrying blades (21a-21d), wherein each blade (21a-21d) extends radially from a root through which it is rigidly attached to the disc up to a heel comprising a platform (26a-26d), the assembly being characterised in that: – it comprises alternating blades (21a, 21c) that are prestressed in the upstream direction and blades (21b, 21d) that are prestressed in the downstream direction, the heel (24c) of each blade (21a, 21c) that is prestressed in the upstream direction tending to be offset in the downstream direction, the heel (24b) of each blade (21b, 21d) that is prestressed in the downstream direction tending to be offset in the downstream direction; – the adjacent pairs of blades having platforms (26a-26d) of which contiguous circumferential ends (27b-27d, 28a-28c) comprise protrusions (29a-29c) and notches (31b-31d) that slot into one another; – each protrusion (29a-29c) being pushed into a notch (31b-31d) in the axial direction (AX) by the prestresses of the blades carrying them.

Description

[0001] Description

[0002] TURBOMACHINE ASSEMBLY COMPRISING PLATFORMS HAVING EDGES PROVIDED WITH COMPLEMENTARY PROTUBERANCES AND NOTCHES AND TURBOMACHINE

[0003] TECHNICAL FIELD

[0004] The invention relates to the reduction of vibrations in a turbomachine bladed disc in service.

[0005] STATE OF THE PRIOR ART

[0006] In such a turbojet 1 shown in Figure 1, 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.

[0007] The primary flow is then compressed in a first and second compression stage 4 and 5 before arriving in a combustion chamber 6, after which it expands by passing through a set of turbines 7 and 8 before being evacuated downstream, generating thrust. The secondary flow is propelled directly rearward by the fan in a vein delimited by the casing 9 to generate additional thrust.

[0008] In practice, such an engine comprises a rotor rotating around its longitudinal axis AX, and including several discs each carrying on its external periphery a series of blades or vanes, these discs corresponding to the fan, the compressors and the turbines.

[0009] As shown in Figure 2, such a blade 11a comprises a root 12a by which it is fixed to a disc (not shown), extended by a blade 13a which extends 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 here carrying two portions of wipers 17a, 18a intended to provide sealing functions.

[0010] The blades carried by the same disc have the same morphology, so that the blade 11b circumferentially contiguous with the blade 11a in figure 2, comprises the same components identified by the same numerical references but supplemented by the letter “b” instead of the letter “a”.

[0011] The outer periphery of a bladed disc is thus delimited by the platforms of the blades it carries, which extend contiguous to each other to jointly delimit a substantially cylindrical peripheral shell.

[0012] In operation, these blades are subjected to high temperatures and significant centrifugal forces, which tend to increase their length in their span direction. Under these conditions, the contiguous platforms, which are joined when the turbomachine is at a standstill, tend to become circumferentially spaced from each other when the turbomachine is in operation, this spacing or clearance being marked J in Figure 2.

[0013] 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.

[0014] Such vibration modes can appear on rotating blades, i.e. blades carried by discs, 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 disc to reduce the gyration of the flow having passed through the rotating blades.

[0015] One solution to dampen 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 platform edges of two adjacent blades remain in contact with 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 makes it possible to dampen these vibration modes by friction.

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

[0017] STATEMENT OF THE INVENTION

[0018] To this end, the invention relates to a turbomachine bladed assembly extending circumferentially around an axis of rotation, and comprising blades, in which each blade extends radially relative to the axis of rotation to a heel located at a free radial end of the blade, this heel comprising a platform, characterized in that:

[0019] - it comprises, circumferentially arranged around the axis of rotation, an alternation of upstream prestressed blades and downstream prestressed blades, each upstream prestressed blade having its heel tending to shift upstream, each downstream prestressed blade having its heel tending to shift downstream;

[0020] - the pairs of circumferentially adjacent blades have platforms whose circumferentially contiguous circumferential end edges have protrusions and notches which fit into each other;

[0021] - each protuberance is in axial contact in a notch receiving it, this contact being maintained by the pre-stresses of the blades which carry them.

[0022] With this arrangement, the blades have to be pre-stressed mainly in the axial direction, which significantly simplifies the implementation of a vibration mode damping solution.

[0023] The invention also relates to a bladed assembly thus defined, in which the protuberances and the notches each have a parallelogram shape overall.

[0024] The invention also relates to a bladed assembly thus defined, in which the protrusions and the notches extend in a direction mainly circumferential with respect to the axis of rotation.

[0025] The invention also relates to a bladed assembly so defined, in which each platform circumferential end edge has a plurality of protrusions or indentations. The invention also relates to a bladed assembly so defined, in which each platform has a circumferential end edge provided with at least one indentation, and another circumferentially opposite circumferential end edge which is provided with at least one protrusion.

[0026] The invention also relates to a bladed assembly thus defined, in which the blades are made of ceramic matrix composite material.

[0027] The invention also relates to a bladed assembly thus defined, in which the blades are prestressed by offsetting along the axis of rotation of their roots relative to the disc which carries them in an essentially axial direction.

[0028] The invention also relates to a bladed assembly so defined, in which the blades are prestressed by being curved upstream or downstream when viewed in a plane containing the axis of rotation.

[0029] The invention also relates to a turbomachine comprising an assembly thus defined.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] - [Fig. 1] is a longitudinal sectional view of a known turbojet engine;

[0032] - [Fig. 2] is a perspective view of two circumferentially adjacent blades equipping a rotating disk according to an arrangement known from the state of the art;

[0033] - [Fig. 3] is a perspective view of two circumferentially adjacent blades equipping a rotating disc according to the invention;

[0034] - [Fig. 4] is a top view of the platforms of four circumferentially adjacent blades according to the invention;

[0035] - [Fig. 5] is a top view partially showing two circumferentially contiguous platforms according to a first variant of the invention;

[0036] - [Fig. 6] is a top view partially showing two circumferentially contiguous platforms according to a second variant of the invention;

[0037] - [Fig. 7] is a top view partially showing two circumferentially contiguous platforms according to a third variant of the invention;

[0038] - [Fig. 8] is a side view of a first example schematically showing the prestressing of a blade by upstream offset; - [Fig. 9] is a side view of a second example schematically showing the prestressing of a blade resulting from a modification of its curvature;

[0039] - [Fig. 10] is a partial view of a turbomachine rotor element equipped with blades according to the invention.

[0040] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0041] The idea behind the invention is to ensure vibration damping by providing platforms having longitudinal edges provided with protuberances and notches which fit together, and that the blades are prestressed alternately upstream and downstream, to axially press these fittings.

[0042] In Figure 3, a blade 21b has a root 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 delimited by two circumferential end edges 27b and 28b in the circumferential direction, these circumferential end edges being the longitudinal edges of the platform.

[0043] Another blade 21c, close to blade 21b in Figure 3 and which has the same morphology, comprises the same elements designated by the same numerical references but terminated by 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 operation.

[0044] As can be seen more clearly in Figure 4, the opposite circumferential end edge 28b of the platform 26b comprises a protrusion 29b or outgrowth which circumferentially extends the platform 26b in the circumferential direction at a level located at half its length along the axis of rotation AX of this blade. This protrusion has a lug shape which protrudes from the edge 28b, being delimited by a contour having the shape of the letter U. This contour shape is given by way of example, since functionally, a shape delimiting two contact surfaces is sufficient. Complementarily, the edge 27c of the platform 26c, which is opposite (in view) the edge 28b, comprises in its central region a notch 31c or housing, the shape of which is complementary to that of the protrusion 29b. This notch also has a U shape, with dimensions slightly larger than those of protuberance 29b in order to accommodate it.The platforms 26b and 26c are thus fitted in the circumferential direction by the engagement of the protuberance 29b in the notch 31b. This shape of notch is also given as an example, since functionally, a shape delimiting two contact surfaces is sufficient.

[0045] As illustrated in Figure 5, the protrusions can have rectangular shapes with rounded ends, and the same applies to the corresponding notches. In general, the protrusions and notches have generally parallelogram shapes.

[0046] Furthermore, and as illustrated in Figure 6, the protrusions and notches may extend in a direction substantially inclined relative to the circumferential direction instead of extending in this circumferential direction.

[0047] In order to increase the contact surfaces, it is also possible to provide, as in Figure 7, that the circumferential end edges of two contiguous platforms are provided, one with several protuberances 29b, 29b', and the other with several corresponding notches 31c, 31c'.

[0048] More generally, each platform has a longitudinal edge, that is to say a circumferential end edge of this platform, provided with a protuberance and its opposite longitudinal edge which is provided with a notch of the same shape, so that all the platforms are fitted together in the circumferential direction.

[0049] Thus, and as seen in Figure 4, a platform 26a of a blade 21a adjacent to the blade 21b has a circumferential end edge 28a which is provided with a protrusion 29a circumferentially engaged in a corresponding notch 31b formed in the circumferential end edge 27b of the platform 26b, which is contiguous to the edge 28a. The opposite circumferential end edge 28b of the platform 26b has its protrusion 29b engaged in the notch 31c of the edge 27c of the platform 26c contiguous to the platform 26b. And similarly, the opposite circumferential end edge 28c of the platform 26c has a protrusion 29c which is engaged in a corresponding notch 31d formed in an adjoining circumferential end edge 27d of another platform 26d carried by a blade 21d circumferentially adjacent to the blade 21c.

[0050] In addition to the nesting of the adjacent platforms with each other by their respective protuberances and notches, these circumferentially adjacent blades are prestressed in opposite directions along the axial direction, as indicated by the arrows in Figure 4. These prestresses make it possible to keep the protuberances and notches in which they are nested in abutment against each other along the axial direction AX.

[0051] More particularly, blades 21b and 21d are pre-stressed to continually tend to shift their platforms downstream, while blades 21a and 21c are pre-stressed to continually tend to shift their platforms upstream.

[0052] The prestressing of a blade upstream can be ensured by shifting its root upstream along the axis AX relative to the other blades, as illustrated schematically in Figure 8. Similarly, the prestressing of a blade downstream can be obtained by shifting its root downstream relative to the other blades. Here, the term "shifting along the axis AX" means a shifting of the blade along its axis of engagement in the disk, this axis of engagement usually called the broaching axis being able to be slightly inclined relative to the axis AX.

[0053] It is also possible to provide on the one hand upstream curved blades so that they are pre-stressed upstream, as illustrated in the example in Figure 9, and on the other hand slightly downstream pre-stressed blades so that they are pre-stressed downstream.

[0054] Thus, different relatively simple solutions exist to obtain different pre-stresses or compensations depending on the axial direction on the blades, these being arranged alternately around the disc to be pre-stressed alternately upstream and downstream.

[0055] The prestress alternation can be obtained by providing an alternation of uncompensated blades and upstream-compensated blades or downstream-compensated blades. When the assembly is mounted, the support exerted by the uncompensated blades on the compensated blades then necessarily generates an alternation of upstream- and downstream-compensated prestress.

[0056] Under these conditions, the protuberances fitted into the corresponding notches axially in contact and bearing on each other make it possible to dampen the vibration modes. More particularly, when the platforms of two circumferentially adjacent blades move circumferentially closer to and further away from each other under the effect of a vibration mode, the axial support of the protuberance of one in the notch of the other generates friction forces which oppose these movements, to dampen the vibration mode, or even to cancel it, by dissipation of energy.

[0057] This damping also works in the case of a vibration mode generating differential displacements of the platforms according to their radial directions (span directions). In addition, in the case of a vibration mode presenting axial displacements, the system limits the vibrations because the vibration amplitude between two adjacent blades is limited by the functional clearance between the protuberance and the notch by which they are connected.

[0058] As will be understood, the degree of prestressing of the blades upstream and downstream is sized to generate a pressing force at the contacts between the ends of the wipers allowing the dissipation of the energy resulting from the vibration modes.

[0059] In the example of Figures 3 and 4, each blade has a circumferential end edge provided with a protrusion and an opposite circumferential end edge provided with a notch, so that the blades have platforms that are all identical. Another possibility could be to provide an alternation comprising on the one hand blades whose circumferential end edges each have a notch and on the other hand blades whose circumferential end edges each have a protrusion. It is also possible to provide several protrusions and notches on the same edge so as to increase the contact surface.

[0060] A bladed assembly comprising blades according to the invention may belong to a turbomachine rotor element, such as the rotor disk DR, part of which is shown in FIG. 10. The blades 21a, 21b may then be mounted by their roots in corresponding cells of this disk DR, constituting a crown of blades 21a, 21b which surround the disk DR while being carried by the latter.

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

Claims

Demands 1. Bladed turbomachine assembly extending conferentially around an axis of rotation (AX) and comprising blades (21a-21d), in which each blade (21a-21d) extends radially with respect to the axis of rotation (AX) to a heel (24b, 24c) located at a free end of the blade (21a-21d) and comprising a platform (26a-26d), characterized in that: - it comprises, circumferentially arranged around the axis of rotation (AX), an alternation of blades (21a, 21c) prestressed upstream and blades (21b, 21d) prestressed downstream, each blade (21a, 21c) prestressed upstream having its heel (24c) tending to shift upstream, each blade (21b, 21d) prestressed downstream having its heel (24b) tending to shift downstream; - the circumferentially adjacent pairs of blades have platforms (26a-26d) whose circumferentially contiguous circumferential ends (27b-27d, 28a-28c) have protuberances (29a-29c) and notches (31b-31d) that fit together with each other; - each protuberance (29a-29c) is in axial contact in a notch (31b-31d) receiving it, this contact being maintained by the prestresses of the blades that support them.

2. Bladed assembly according to claim 1, wherein the protuberances (29a-29c) and the notches (31a-31c) each have an overall parallelogram shape.

3. Bladed assembly according to claim 2, wherein the protrusions (29a-29c) and the notches (31a-31c) extend in a predominantly circumferential direction with respect to the axis of rotation (AX).

4. Bladed assembly according to any one of claims 1 to 3, wherein each circumferential end edge (28b, 27c) of platform has several protrusions (29b, 29b') or several notches (31c, 31c').

5. Bladed assembly according to any one of claims 1 to 4, wherein each platform (26a-26d) has a circumferential end edge (27b-27d) having at least one notch (31b-31d), and another circumferentially opposite circumferential end edge (28a-28c) which has at least one protrusion (29a-29c).

6. Bladed assembly according to any one of claims 1 to 5, wherein the blades are made of ceramic matrix composite material.

7. Bladed assembly according to any one of claims 1 to 6, wherein the blades are prestressed by offsetting their feet along the axis of rotation relative to the disk that carries them.

8. Bladed assembly according to any one of claims 1 to 7, wherein the blades are prestressed by being curved upstream or downstream when viewed in a plane containing the axis of rotation.

9. Turbomachine comprising a bladed assembly according to any one of claims 1 to 8.

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