Turbomachine assembly comprising platform having edge provided with complementary protrusions and notches, and associated turbomachine

Abstract

The object of the invention is a bladed turbine assembly extending about an axis (AX), the turbine comprising a disk carrying blades (21a-21d), where each blade (21a-21d) extends radially from a root to a heel comprising a platform (26a-26d), each blade being rigidly connected to the disk through the root, the platform (26a-26d) being rigidly connected to the disk through the root. The invention is characterized in that:-the turbine assembly comprises blades (21a, 21c) which are prestressed towards the upstream and blades (21b, 21d) which are prestressed towards the downstream, each blade (21a, 21c) which is prestressed towards the upstream displaces its root (24c) towards the upstream, each blade (21b, 21d) which is prestressed towards the downstream displaces its root (24c) towards the upstream, and each blade (21b, 21d) which is prestressed towards the downstream displaces its root (24c) towards the downstream. 21d) with its heel (24b) tending to displace towards the downstream; -a pair of circumferentially adjacent blades having platforms (26a-26d), the circumferentially adjacent ends (27b-27d, 28a-28c) of the platforms comprising protrusions (29a-29c) and notches (31b-31d) that cooperate together; -each projection (29a-29c) is pressed into a recess (31b-31d) in the axial direction (AX) by the prestress of the blade carrying the projection, the recess receiving the projection.

Description

Technical Field

[0001] The present invention relates to reducing vibrations in a bladed turbine disk during use. Background Art

[0002] exist Figure 1 In the turbojet engine 1 shown, external air enters an air intake duct 2 to pass through a fan 3 comprising a series of rotating airfoils and is then divided into a central main airflow and a bypass airflow surrounding the main airflow.

[0003] Next, the main airflow is compressed in the first compression stage 4 and the second compression stage 5, and then reaches the combustion chamber 6, after which the main airflow expands while passing through a set of turbines 7 and 8, and then is discharged downstream while generating thrust. The bypass airflow is directly propelled backward by the fan in the jet defined by the casing 9 to generate complementary thrust.

[0004] In practice, such an engine comprises a rotor rotating about a longitudinal axis AX of the engine, the rotor comprising a plurality of disks, each carrying at its periphery a series of blades or airfoils, these disks corresponding to the fan, the compressor and the turbine.

[0005] like Figure 2 As shown, such a blade 11a comprises a root 12a by which the blade is fastened to a disk (not shown), the root 12a being extended by an airfoil 13a extending along a spanwise direction EVa radial to the axis of rotation. This airfoil 13a terminates in a heel 14a comprising a platform 16a or in this case a heel carrying two parts of fins 17a, 18a intended to ensure a sealing function.

[0006] The blades carried by the same disk have the same shape, making them Figure 2 The blade 11a in the figure is circumferentially adjacent to the blade 11b, which comprises the same parts indicated by the same reference numerals but with the letter b instead of the letter a.

[0007] The outer periphery of the bladed disk is thus defined by the platforms of the blades carried by the disk, the platforms extending adjacent to one another to jointly define a generally cylindrical outer peripheral shroud.

[0008] During operation, these blades are subject to high temperatures and significant centrifugal stresses, which tend to increase the length of the blades in the spanwise direction of the blades. Under these conditions, when the turbine is stopped, adjacent platforms that were in contact with each other tend to be circumferentially spaced apart from each other when the turbine is running, with the spacing or gap being about 1 / 4 of a 1 / 2 inch. Figure 2 Marked as J in the middle.

[0009] Considering the presence of vibration excitations in such a turbine, this situation leads to vibration modes of the blades due to which the platforms of the blades tend to collide circumferentially with each other, which can degrade the blades.

[0010] This vibration mode can occur on rotating blades (i.e. blades carried by a disk), but also on stationary blades, i.e. blades carried by a fixed element such as a rectifier, which is located downstream of the bladed disk of, for example, a fan or compressor, to reduce the swirl of the flow that has passed through the rotating blades.

[0011] One solution for damping the vibration modes is to apply a torsional prestress to each disk during the installation of the blades on the disk. In this case, the platform tends to rotate about its span axis so that the edges of the platforms of two adjacent blades remain bearing against each other despite the effects of centrifugal stresses and thermal expansion. During operation, the vibration modes of the blades generate friction at the bearing points of the platforms, which makes it possible to damp these vibration modes by friction.

[0012] In this context, the object of the invention is to provide a solution for limiting the vibration modes of a bladed disk, in particular in the case of blades made of ceramic matrix composites, the acceptable prestress of which is lower than that of blades made of metal alloys. Summary of the invention

[0013] To this end, the object of the invention is a turbine assembly with blades extending circumferentially around an axis of rotation and comprising blades, wherein each blade extends radially relative to the axis of rotation up to a heel, which is located at the free radial end of the blade and comprises a platform, characterized in that:

[0014] The turbine assembly comprises blades prestressed upstream and blades prestressed downstream arranged alternately circumferentially around the axis of rotation, the heel of each blade prestressed upstream tending to be displaced upstream, and the heel of each blade prestressed downstream tending to be displaced downstream;

[0015] - pairs of circumferentially adjacent blades have platforms, the circumferential adjoining edges of the circumferential ends of the platforms comprising projections and recesses that fit together;

[0016] - Each protrusion is in axial contact in the recess housing it, this contact being maintained by the prestress of the blade carrying the protrusion.

[0017] With this arrangement, the blades must be prestressed substantially in the axial direction, which significantly simplifies the implementation of the solution for damping the vibration modes.

[0018] The invention also relates to a bladed assembly as defined herein, wherein the projection and the recess each have the shape of a parallelogram as a whole.

[0019] The invention also relates to a bladed assembly as defined herein, wherein the projections and recesses extend in a direction that is substantially circumferential relative to the axis of rotation.

[0020] The invention also relates to a bladed assembly defined in this way, wherein each edge of the circumferential end of the platform comprises a plurality of protrusions or a plurality of indentations.

[0021] The invention also relates to a bladed assembly defined in this way, wherein each platform comprises one circumferential end edge provided with at least one notch and another circumferentially opposite circumferential end edge provided with at least one protrusion.

[0022] The invention also relates to a bladed assembly as defined herein, wherein the blades are made of a ceramic matrix composite material.

[0023] The invention also relates to a bladed assembly as defined herein, wherein the blade is prestressed by offsetting its root along the axis of rotation relative to a disk carrying the blade in a substantially axial direction.

[0024] The invention also relates to a bladed assembly defined in this way, wherein the blades are prestressed by bending towards upstream or towards downstream when viewed in a plane containing the axis of rotation.

[0025] The invention also relates to a turbomachine comprising an assembly thus defined. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] -[ Figure 1 ] is a longitudinal cross-sectional view of a known turbojet engine;

[0027] -[ Figure 2 ] is a perspective view of two circumferentially adjacent blades arranged in a rotating disk according to an arrangement known in the prior art;

[0028] -[ Figure 3 ] is a perspective view of two circumferentially adjacent blades arranged in a rotating disk according to the present invention;

[0029] -[ Figure 4 ] is a top view of the platform of four circumferentially adjacent blades according to the present invention;

[0030] -[ Figure 5 ] is a top view partially showing two circumferentially adjacent platforms according to a first alternative embodiment of the present invention;

[0031] -[ Figure 6 ] is a top view partially showing two circumferentially adjacent platforms according to a second alternative embodiment of the present invention;

[0032] -[ Figure 7] is a top view partially showing two circumferentially adjacent platforms according to a third alternative embodiment of the present invention;

[0033] -[ Figure 8 ] is a side view of a first example, schematically illustrating prestressing of the blade by deflecting it toward upstream;

[0034] -[ Fig. 9 ] is a side view of a second example, schematically illustrating the application of prestress to the blade due to a change in the curvature of the blade;

[0035] -[ Fig.10 ] is a partial view of a turbine rotor element equipped with blades according to the invention. DETAILED DESCRIPTION

[0036] The idea underlying the invention is to ensure vibration damping by providing a platform with longitudinal edges provided with protrusions and recesses fitting together, and the blades are alternately prestressed upstream and downstream to press the fit axially together.

[0037] exist Figure 3 , the blade 21b comprises a root 22b, by which the blade 21b is fastened to a disk (not shown), the root 22b being extended by an airfoil 23b extending along a spanwise direction EVb radial to the axis of rotation of the disk. The airfoil 23b terminates in a heel 24b comprising a platform 26b, the platform 26b being defined in the circumferential direction by two edges of circumferential ends 27b and 28b, these edges of the circumferential ends being the longitudinal edges of the platform.

[0038] and Figure 3 Another blade 21c adjacent to the blade 21b in the embodiment and having the same form comprises the same elements denoted by the same reference numerals but with the letter c instead of the letter b. The two blades are carried by the same disk, not shown, which rotates about the axis of rotation when the engine is running.

[0039] As in Figure 4 As can be seen more clearly in FIG. 2 , the opposite circumferential end edge 28b of the platform 26b comprises a protrusion 29b or projection which extends the platform 26b circumferentially in the circumferential direction to half the length of the blade along the axis of rotation AX of the blade. The protrusion has the shape of a lug extending beyond the edge 28b while being defined by a profile having the shape of the letter U. The profile shape is given as an example, it being understood that functionally, a shape defining two contact surfaces is sufficient.

[0040] Furthermore, the edge 27c of the platform 26c facing the edge 28b comprises in its central region a recess 31c or a housing, the shape of which is complementary to the shape of the protrusion 29b. This recess also has a U-shape, the dimensions of which are slightly larger than the dimensions of the protrusion 29b to accommodate the protrusion 29b. Thus, by inserting the protrusion 29b into the recess 31b, the platforms 26b and 26c fit together in the circumferential direction. This recess shape is also given as an example, it being understood that, functionally, a shape defining two contact surfaces is sufficient.

[0041] like Figure 5 As shown, the protrusion can have a rectangular shape with rounded edges, and the corresponding recess also has a rectangular shape with rounded edges. Typically, the protrusion and the recess have a parallelogram shape as a whole.

[0042] In addition, if Figure 6 As shown, the protrusions and recesses may extend in a direction that is substantially inclined relative to the circumferential direction, rather than extending in the circumferential direction.

[0043] In order to increase the contact surface, such as Figure 7 As shown, one of the edges of the circumferential ends of two adjacent platforms may also be provided with a protrusion 29b, 29b', while the other edge has a plurality of corresponding recesses 31c, 31c'.

[0044] More generally, each platform comprises a longitudinal edge provided with a protrusion (i.e., the edge of the circumferential end of the platform) and a longitudinal edge opposite to the longitudinal edge, the opposite longitudinal edge being provided with a recess having the same shape, so that all platforms fit together with each other along the circumferential direction.

[0045] Therefore, if Figure 4 As can be seen in the figure, the platform 26a of the blade 21a adjacent to the blade 21b comprises a circumferential end edge 28a provided with a projection 29a which is inserted circumferentially into a corresponding recess 31b formed in a circumferential end edge 27b of the platform 26b which adjoins the edge 28a. The projection 29b of the opposite circumferential end edge 28b of the platform 26b is inserted into a recess 31c of an edge 27c of the platform 26c which adjoins the platform 26b. Likewise, the opposite circumferential end edge 28c of the platform 26c comprises a projection 29c which is inserted into a corresponding recess 31d formed in an adjacent circumferential end edge 27d of another platform 26d carried by the blade 21d which adjoins the blade 21c circumferentially.

[0046] In addition to the adjacent platforms being fitted together via their respective protrusions and recesses, the circumferentially adjacent blades are prestressed in opposite directions along the axial direction, such as Figure 4 These prestresses make it possible to keep the protrusion and the recess cooperating with the protrusion against each other along the axial direction AX.

[0047] More specifically, blades 21b and 21d are prestressed so as to continuously tend to displace the platforms of blades 21b and 21d towards downstream, whereas blades 21a and 21c are prestressed so as to continuously tend to displace the platforms of blades 21a and 21c towards upstream.

[0048] The upstream prestressing of the blades can be ensured by offsetting the root of the blades relative to the other blades along the axis AX upstream, as shown in Figure 8 In a similar manner, the prestressing of the blades towards the downstream can be obtained by offsetting the root of the blades towards the downstream relative to the other blades. The offset along the axis AX here refers to the offset of the blade along the axis of its insertion into the disk, wherein this insertion axis is usually called the setting axis and can be slightly inclined relative to the axis AX.

[0049] It is also possible to provide blades that are curved toward upstream so that they are prestressed toward upstream, such as Fig. 9 As shown in the example of , on the other hand, blades are provided which are slightly prestressed toward downstream, so that the blades are prestressed toward downstream.

[0050] Therefore, there are various relatively simple solutions to obtain different prestresses or compensations along the axial direction on the blades, which are arranged in an alternating manner around the disk so as to be alternately prestressed upstream and downstream.

[0051] The alternation of prestress can be obtained by alternately providing blades without compensation and blades with compensation directed upstream or with compensation directed downstream. Thus, when the assembly is mounted, the bearing exerted by the non-compensating blades on the compensating blades necessarily produces an alternation of prestress directed upstream and downstream.

[0052] Under these conditions, the protrusions that fit into the corresponding recesses that are in axial contact and bearing with each other enable the vibration mode to be damped. More specifically, when the platforms of two circumferentially adjacent blades move circumferentially closer to or away from each other under the effect of the vibration mode, the axial bearing of the protrusion of one blade in the recess of the other blade generates friction stresses that oppose these movements to damp or even cancel the vibration mode by dissipating energy.

[0053] This damping also works in the case of vibration modes that cause different movements of the platform according to its radial direction (spanwise). In addition, in the case of vibration modes with axial movement, the system limits the vibrations because the vibration amplitude between two adjacent blades is limited by the functional gap between the protrusions and recesses connecting these two adjacent blades.

[0054] As will be appreciated, the degree to which the blades are prestressed upstream or downstream is sized to produce a compressive stress at the contact between the ends of the fins, thereby dissipating the energy generated by the vibration mode.

[0055] exist Figure 3 and Figure 4 In the example of , each blade comprises a circumferential end edge provided with a protrusion and an opposite circumferential end edge provided with a notch, so that the blades have all the same platform. Another possibility may involve providing an alternative solution, which comprises, 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 multiple protrusions and notches on the same edge to increase the contact surface.

[0056] A bladed assembly comprising a blade according to the invention may belong to a turbine rotor element, such as a rotor disk DR, a portion of which is located at Fig.10 Thus, the blades 21a, 21b can be mounted in respective cells of the disk DR by means of the roots of the blades 21a, 21b, while forming a ring of blades 21a, 21b which surrounds the disk DR when carried by the disk DR.

[0057] Generally, the invention is shown for a rotary blade comprising a platform and at least one fin portion made of CMC type material, but it is also applicable to blades made of metal alloys.

Claims

1. A bladed turbine assembly extending circumferentially about an axis of rotation (AX) and comprising blades (21a-21d), wherein: Each blade (21a-21d) extends radially relative to the rotation axis (AX) up to a heel (24b, 24c) located at the free end of the blade (21a-21d) and comprising a platform (26a-26d), characterized in that: - the turbine assembly comprises blades (21a, 21c) prestressed upstream and blades (21b, 21d) prestressed downstream arranged alternately in the circumferential direction around the rotation axis (AX), the heel (24c) of each blade (21a, 21c) prestressed upstream tending to be displaced upstream, and the heel (24b) of each blade (21b, 21d) prestressed downstream tending to be displaced downstream; - pairs of circumferentially adjacent blades have platforms (26a-26d), and circumferentially adjacent edges (27b-27d, 28a-28c) of circumferential ends of the platforms include protrusions (29a-29c) and recesses (31b-31d) that fit together; - Each protrusion (29a-29c) is in axial contact in the recess (31b-31d) housing said protrusion, this contact being maintained by the prestress of the blade carrying said protrusion.

2. The bladed assembly according to claim 1, wherein: The protrusions (29a-29c) and the recesses (31a-31c) each have a parallelogram shape as a whole.

3. The bladed assembly according to claim 2, wherein: The protrusions (29a-29c) and the recesses (31a-31c) extend in a generally circumferential direction relative to the axis of rotation (AX).

4. The bladed assembly according to any one of claims 1 to 3, wherein: Each edge (28b, 27c) of the circumferential end of the platform includes a plurality of protrusions (29b, 29b') or a plurality of notches (31c, 31c').

5. The bladed assembly according to any one of claims 1 to 4, wherein: Each platform (26a-26d) includes one circumferential end edge (27b-27d) provided with at least one notch (31b-31d) and another circumferentially opposite circumferential end edge (28a-28c) provided with at least one protrusion (29a-29c).

6. The bladed assembly according to any one of claims 1 to 5, wherein: The blade is made of a ceramic-based composite material.

7. A bladed assembly according to any one of claims 1 to 6, wherein: The blades are prestressed by offsetting their roots along the axis of rotation relative to the disk carrying the blades.

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

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

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