Device for axially retaining moving blades of an lp turbine in the recesses of a rotor disc of the lp turbine, and method for assembling said moving blades

Abstract

One aspect of the invention relates to a device (30) for axially retaining a moving blade (10) of a low-pressure turbine in a recess (21) of a rotor disc of axis (X) of the turbine. This device comprises a stop part (40) intended to extend between an upstream face (11a) of a blade root (11) of the moving blade (10) and a downstream face (11b) of the root of the moving blade, the stop part (40) comprising: - a first wall (41) which forms an end stop for the upstream face (11a) of the blade root (11), - a second wall (42) which forms an end stop for the downstream face (11b) of the blade root (11), and - a connection surface (43) intended to extend between the first and the second wall (41, 42) along a radially inner end face (11c) of the blade root (11). Further features of the invention relate to a turbomachine rotor assembly and to a method for assembling moving blades (10) in the recesses (21) of an LP turbine rotor disc.

Description

DESCRIPTION TITLE: Axial retention device for the moving blades of a low-pressure turbine in the recesses of a rotor disk of the low-pressure turbine and method for mounting these moving blades TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a device for axially retaining the moving blades of a low-pressure (LP) turbine in the recesses of the LP turbine's rotor disc. It also relates to a method for mounting these moving blades in the rotor disc.

[0002] The invention has applications in the field of aeronautics and, in particular, in the field of low-pressure turbines for aircraft turbomachinery. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] A low-pressure (LP) turbine is known to comprise several successive impellers, separated by distributor stages. An impeller, also called a wheel, consists of moving blades and a rotor disc. The outer periphery of the rotor disc has mounting grooves, called recesses, which extend in substantially axial directions (i.e., at an angle of up to a few degrees to the axial direction). Each recess is designed to receive the root of a moving blade, which is pressed into the recess.

[0004] Typically, a first axial retaining ring, or flange, is arranged on the upstream face of the turbine disk, and a second axial retaining ring is arranged on the downstream face of the turbine disk. These rings form axial stops for the blade roots housed in the recesses. An example of a section of a low-pressure turbine comprising three impellers 1a, 1b, 1c according to the prior art is shown in Figure 1. The impellers 1a, 1b, 1c are separated from each other by distributors 7, 8, each equipped with a ferrule 9, 10 forming the inner wall of the flow channel F. Each impeller 1a, 1b, 1c comprises a disk rotating around the central axis of the turbine, schematically represented by the axis X, and having an outer peripheral rim 2a, 2b, 2c, to which the blades are fixed by their feet 3a, 3b, 3c. In particular, a first wheel 1a has a movable blade 4a mounted axially, by its foot 3a, in a recess 6a of the rim 2a of the disc. The foot 3a of the blade 4a is blocked axially, upstream, by an annular flange 13 and, downstream, by an annular flange 14, the flanges 13 and 14 being of different types.

[0005] These flanges and / or rods, which provide axial support for the feet 3a, 3b, 3c of the blades 4a, 4b, 4c, must be secured along said blades. In some cases, axial support for the flange or rod is ensured by a beak, or hook, with a relatively complex shape. In other cases, axial support is achieved by means of a locking mechanism.

[0006] Nowadays, moving blades are often made of a ceramic matrix composite (CMC), which has the advantage of being lightweight. CMC blades are therefore lighter than conventional metal blades. However, manufacturing CMC blades with a hook is complex because it involves weaving and requires forming two textured layers on the blade, at the platform 5a, 5b, 5c located between the blade and the blade root 3a, 3b, 3c. One layer forms the surface delimiting the air stream and the hook, and the other serves to prevent blade tipping and provide downstream overlap. Furthermore, the transfer of the centrifugal force from a flange or axial stop bead by a hook integrated into the blade leads to centrifugal mechanical loading, which is detrimental to the CMC hook.

[0007] In the case of a retention by dog ​​lock, the sealing of the impeller must be advanced to the foot of the low pressure distributors (LPD), which creates a lack of space to integrate axial stop solutions at the rear of the blades, i.e. on the downstream face of the blade feet.

[0008] There is therefore a real need for an axial retention device for the blade feet in the disc recesses which does not require the manufacture of a CMC hook, nor the advancement of the sealing at the foot of the DBP. SUMMARY OF THE INVENTION

[0009] To address the problems mentioned above regarding the axial retention of the moving blade foot in the disk cavity, the applicant proposes a stop piece positioned between the blade foot and the bottom of the disk cavity and extending between the upstream and downstream faces of the blade foot.

[0010] In the following description, the terms "upstream" and "downstream" are defined with respect to the direction of air flow from the air inlet to the air outlet of the LP turbine. In other words, upstream and downstream are understood along a central axis X with respect to the general direction of the operating gases.

[0011] In the description, the term "exterior" refers to the surfaces or parts of parts furthest from the central X axis of the turbomachine air stream (i.e., the axis of rotation of the fan blades), as opposed to the term "interior" which refers to the surfaces and parts of parts closest to said central X axis.

[0012] According to a first aspect, the invention relates to an axial retention device for a moving blade of a low-pressure turbine in a cavity of a rotor disk of the shaft of said turbine, characterized in that it comprises, a stop piece intended to extend between an upstream face of a blade root of the moving blade and a downstream face of said blade root, said stop piece comprising: a first wall which forms a stop for the upstream face of the blade root, a second wall which forms a stop for the downstream face of the blade root, and a connecting surface intended to extend between the first and second walls, along a radially internal end face of the blade root.

[0013] This device allows for axial stopping or locking of the blade roots within the disc's recesses without requiring any hooks on the blade or any specific parts on the downstream face of the impeller. It thus eliminates the need for an axial retaining ring, the centrifugal force of which would have to be absorbed by a hook integrated into the CMC blade. Furthermore, it has the advantage of a compact design, saving space downstream of the blade root and thus allowing room for axial sealing.

[0014] In addition to the characteristics mentioned in the preceding paragraph, the axial retention device according to one aspect of the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: The retaining piece is a single-piece metal component. The first wall of the retaining piece has a width or height dimension that is greater than another width or height dimension of the second wall, the dimensions being taken in a plane transverse to the mating surface. The first wall is configured to extend partially over an upstream face of the rotor disk. The first wall of the retaining piece extends perpendicularly on either side of the mating surface. The second wall of the retaining piece extends perpendicularly to the mating surface so as to cover a downstream face of a blade root.

[0015] A second aspect of the invention relates to a turbomachine rotor assembly comprising an X-axis rotor disk which has hollows cut out at its periphery and movable blades mounted in hollows of the disk, two circumferentially adjacent hollows around the disk each delimiting a tooth of the disk, characterized in that it comprises: several stop pieces as defined above, each stop piece being intended to axially retain a movable blade in a corresponding hollow of the disk, and, means for locking the stop pieces against the disk, the first wall of each stop piece extending circumferentially so as to be in contact with at least one upstream face of a tooth of the rotor disk.

[0016] Advantageously, this assembly may include the following features, considered individually or according to all technically possible combinations: the disc includes a cavity cut into the disc and the first wall includes a hook mounted by interlocking in the cavity. It comprises a plurality of retaining pieces, each arranged in a recess of the disk and configured so that their first walls are circumferentially arranged end to end around the X-axis. It includes a retaining ring fixed to the disk and mounted around the entire circumference of the rotor disk, against the first walls of the retaining pieces, so as to hold the retaining pieces in position within the disk recesses. It further comprises a retaining circlip housed in a groove of the rotor disk, at an inner end of the retaining ring, the retaining circlip being configured to secure the retaining ring to the disk after the retaining ring has been mounted on the disk.

[0017] A third aspect of the invention relates to a method of mounting low-pressure turbine moving blades in the recesses of a rotor disk of said turbine, characterized in that it comprises, for each moving blade, the following steps: installation of a stop piece as defined above against a radially internal end face of a blade foot, and installation of the moving blade equipped with the stop piece in a recess of the rotor disk.

[0018] This method has the advantage of being relatively simple to implement.

[0019] Advantageously, the process involves the following operations: installation of the retaining ring in a groove of the rotor disc, and installation of a retaining ring on the disc along the first walls of the retaining piece, the retaining ring being held in position by a locking action performed by the retaining ring. BRIEF DESCRIPTION OF THE FIGURES

[0020] Other advantages and features of the invention will become apparent from the following description, illustrated by the figures in which:

[0021] Figure 1, already described, represents a schematic longitudinal cross-sectional view of part of a BP turbine with several blade wheels according to the prior art;

[0022] Figure 2 shows a longitudinal cross-sectional view of the axial retaining device according to the invention, with a stop piece mounted between a blade foot and a disc cavity;

[0023] Figure 3 shows a schematic upstream view and a schematic downstream view of a stop piece of the axial retaining device according to the invention, mounted between a blade foot and a disc cavity;

[0024] Figure 4 shows several cross-sectional views, upstream or downstream, of various embodiments of the stop piece according to the invention;

[0025] Figures 5A, 5B and 5C represent, respectively, a cut perspective view, an upstream view and a downstream view of an embodiment of the axial restraint device according to the invention;

[0026] Figure 6 shows, in perspective views, several stages of the assembly process for the movable blades according to the invention; and

[0027] Figure 7 shows a perspective view of several movable blades mounted in a rotor disk with the axial retaining device according to the invention. DETAILED DESCRIPTION

[0028] An example of an axial retention device for moving blades of a low-pressure turbine is described in detail below, with reference to the accompanying drawings. This example illustrates the features and advantages of the invention. It should be noted, however, that the invention is not limited to this example.

[0029] In the figures, identical elements are identified by identical references. For the sake of readability, the size scales between represented elements are not respected.

[0030] An example of an axial retaining device according to the invention is shown in cross-section in Figure 2. This axial retaining device 30 comprises, for each movable blade 10, a stop piece 40 configured to be housed between the foot 11 of the blade 10 and the recess 21 of the disk 20 of the BP turbine rotor. This piece The stop 40 extends between the upstream face 11a of the blade foot 11 and the downstream face 11b of this blade foot. For this purpose, the stop piece 40 comprises: a first wall 41, also called the upstream wall, configured to be positioned at least partially along the upstream face 11a of the blade foot, a second wall 42, also called the downstream wall, configured to be positioned at least partially along the downstream face 11b of the blade foot, and a connecting surface 43 axially connecting (i.e. along the central axis (X)) the upstream wall 41 and the downstream wall 42, along the internal face 11c of the blade foot.

[0031] The upstream and downstream walls of the retaining piece 40 can, for example, be made of metal or an alloy, such as one of the superalloys commonly used in this area of ​​the turbine. The upstream walls 41 and downstream walls 42 are, for example, square or rectangular in shape. The connecting surface 43 can be a plate, preferably made of the same metal or alloy as the upstream and downstream walls. The connecting surface 43 is preferably rectangular, with an axial dimension substantially greater than the axial dimension of the blade root 11. The upstream walls 41 and downstream walls 42, as well as the connecting surface 43, can be made in one piece so that the retaining piece 40 is a single unit.

[0032] In some embodiments, the upstream wall 41 and the downstream wall 42 of the retaining piece have similar dimensions. In other embodiments, the upstream wall 41 and the downstream wall 42 have different dimensions, with the upstream wall 41 being larger than the downstream wall 42. Indeed, as shown in the example in Figures 2 and 3, the upstream wall 41 can extend radially (i.e., along an axis perpendicular to the X-axis) in front of the upstream face 11a of the blade root and in front of the portion of the upstream face of the disc 20 below the cavity. The upstream wall 41 can thus extend parallel to the upstream opening 21a of the cavity 21 and to the inner portion of the upstream face of the disc 20 (the inner portion being the part of the disc without inter-cavity teeth 22). In this example, the downstream wall 42 extends radially in front of the downstream opening 21 b of the alveolus 21, that is, along the downstream face 11 b of the blade foot.The stop piece 40 thus presents, in. The example of figures 2 and 3, an inverted T-shaped section, with an upstream wall 41 extending radially on either side of the connecting surface 43 and a downstream wall 42 extending radially towards the platform 12 of the blade 10. With such a configuration, the upstream wall 41 is blocked, upstream, by the disc 20 so that the entire stop piece 40 is axially blocked upstream.

[0033] The axial retaining device 30 of the invention may include, in addition to the stop piece 40, a flange 50, or retaining ring, mounted radially along the upstream face 20a of the disc 20. This flange 50, of annular shape, extends parallel to the alveoli 21 and the inter-alveoli teeth 22 of the disc 20 over the entire circumferential length of the disc. This flange 50, whose shape is classic for a BP turbine flange, has a hook 51 partially housed in a groove 23 of the disc 20. This hook 51 ensures the attachment of the flange 50 to the disc 20. Thus mounted along the disc 20, the flange 50 extends upstream of the upstream wall 41 of the stop piece 40 so as to prevent any axial movement, from downstream to upstream, of the stop piece 40.

[0034] It is therefore understood that the stop piece 40 is axially blocked in a bidirectional manner, that is to say, both from upstream to downstream and from downstream to upstream. Thus, the blade foot 11, positioned inside the stop piece 40, is also axially blocked in a bidirectional manner.

[0035] In some embodiments, the axial retaining device 30 also includes an axial retaining ring 60 housed in the groove 23 of the disc 20. This axial retaining ring 60 is a substantially annular part made of a flexible, substantially elastic material, such as the superalloys commonly used in turbines. The axial retaining ring 60 has a radial slot extending over its entire cross-section. This radial slot allows it to be lowered into the groove 23 to insert (or remove) the flange 50.

[0036] Figure 4 illustrates embodiments in which the stop piece 40 has different shapes. Drawing A in Figure 4 shows, in cross-section, an example of a stop piece 40 comprising an upstream wall 41 equipped with a shoulder 44 that fits inside the disc 20. This shoulder 44, also called a hook, is formed by an axial extension extending at a substantially right angle in line with the upstream wall 41. This axial extension is configured to fit into a suitable housing 24 located at the entrance of the groove 23 of the disc 20. Viewed in section, the shoulder 44 has a hook shape, a portion of which is housed in the disc 20. In other words, the shoulder 44 fits into the disc, under the recess 21 receiving the stop piece 40, partially fitting the inner perimeter of the recess 21 of the disc 20, so that the centrifugal force of the stop piece 40 is taken up by the disc and the blade 10 is partially relieved of this force.

[0037] Drawings B and C of Figure 4 show, respectively, a cross-sectional view and a schematic upstream view, an example of a retaining piece 40 in which the upstream wall 41 extends radially to the platform 12 of the blade 10 so as to create a partial seal of the recesses 21. In this embodiment, the retaining piece 40 has a substantially U-shaped cross-section, with an upstream wall 41 extending in a single radial direction from the connecting surface 43; the upstream wall 41 extends further radially than the downstream wall 42, reaching the platform 12 of the blade. The axial blocking, or stopping, downstream is achieved, in this embodiment, by blocking the upstream wall 41 against the teeth 22 of the disc 20.

[0038] Drawing D in Figure 4 shows, in a schematic view from the downstream side, an example of the retaining piece 40 in which the downstream wall 42 extends radially on either side of the connecting surface 43. In this embodiment, the downstream wall 42 extends not only in front of the upstream face 11a of the blade root, but also in front of the upstream face of the disc 20 under the recess 21. The downstream wall 42 thus contributes to the upstream axial blocking of the retaining piece 40.

[0039] Of course, the various embodiments described above can be combined with each other such as, for example, the upstream wall 41 of drawing C combined with the downstream wall 42 of drawing D, or the upstream wall with the shoulder 44 of drawing A combined with the downstream wall 42 of drawing D, etc.

[0040] The embodiment of drawing B in Figure 4 is shown in Figure 5A, in Figure 5B, in Figure 5A, in Figure 5B, and in Figure 5C, in Figure 5C, in Figure 5A. These views show a stop piece 40 with a roughly U-shaped cross-section, mounted in a recess 21 of the disc 20, under the blade foot 11, so as to cover the face upstream 11a of the blade foot 11, downstream face 11b of the blade foot and the inner face 11c of said blade foot. Figure 5A also shows the groove 23 of the disc 20 in which the retaining ring 60 and the flange 50 are housed, said retaining ring 60 being positioned at the inner end of the flange 50.

[0041] Regardless of the shape and dimensions of the upstream and downstream walls of the stop piece 40, the axial retaining device 30 is mounted as shown in Figure 6. The mounting method according to the invention comprises the following steps, represented by drawings E to H: Drawings E: manufacturing of the stop piece 40 with its upstream wall 41 and its downstream wall 42 connected by the connecting surface 43; Drawings F: installation of the stop piece 40 under the blade foot 11, that is to say against the inner face 11c of the foot 11 of the blade 10; Drawing G: Installation of the movable blade 10 equipped with the stop piece 40 in a recess 21 of the disc 20, the upstream wall 41 of the stop piece being in contact with the teeth 22 located on either side of the recess 21; and Drawings H (for the embodiments concerned and after all the blades have been mounted): installation of the flange 50 in the groove 23 of the disc 20, along the upstream wall 41, the flange 50 being installed after the stop ring 60 has been positioned in the groove 23.

[0042] Once all the movable blades 10, each equipped with a stop piece 40, have been mounted in the recesses 21 of the disc 20, the upstream walls 41 of all the stop pieces 40 are positioned side by side, circumferentially, one after the other. An example of several juxtaposed upstream walls 41 is shown in Figure 7. Although, for clarity, only two blade feet 11 are shown in this Figure 7, several upstream walls 41 are shown side by side, each forming part of one of the stop pieces 40 housed in the recesses 21 of the disc 20. Figure 7 also shows the flange 50 mounted along the upstream walls 41 and forming an axial restraint (from downstream to upstream) of the stop pieces 40 and, consequently, of the blade feet 11. The flange 50 not only ensures the axial stopping of the blade feet 11, via the stop pieces 40, but also the ventilation of the alveoli 21 of the disc.Indeed, the ventilation of the. The 21 alveoli of the disc 20 are necessary during the operation of the turbomachine given the high temperature of the gases circulating in the flow channel of the BP turbine.

[0043] Although described through a number of examples, variants and embodiments, the axial restraint device according to the invention includes various variants, modifications and improvements which will be obvious to a person skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.

Claims

DEMANDS

1. A turbomachine rotor assembly comprising a rotor disk (20) with axis (X) having recesses (21) machined around its periphery and movable blades (10) mounted in recesses (21) of the disk, two circumferentially adjacent recesses around the disk each defining a tooth of the disk, characterized in that it comprises several retaining pieces (40) intended to extend between an upstream face (11a) of a blade root (11) of the movable blade (10) and a downstream face (11b) of said blade root, said retaining pieces (40) comprising: - a first wall (41) which forms a stop for the upstream face (11 a) of the blade foot (11 ), - a second wall (42) which forms a stop for the downstream face (11 b) of the blade foot (11), and - a connecting surface (43) intended to extend between the first and second walls (41, 42), along a radially internal end face (11c) of the blade foot (11), - each retaining piece (40) being designed to axially hold a movable blade (10) in a corresponding recess of the disc (20), and, - means for locking (50, 60) the stop pieces against the disc (20), - the first wall (41) of each stop piece (40) extending circumferentially so as to be in contact with at least one upstream face of a tooth (22) of the rotor disc, - a plurality of stop pieces (40) each arranged in a cavity (21) of the disk (20) and configured so that their first walls (41) are circumferentially arranged end to end, around the axis (X), - a retaining ring (50) fixed to the disc and mounted around the entire circumference of the rotor disc (20), against the first walls (41) of the stop pieces (40) so as to hold the stop pieces (40) in position in the recesses of the disc.

2. Assembly according to claim 1, characterized in that the stop piece (40) is a one-piece metal piece.

3. Assembly according to claim 1 or 2, characterized in that the first wall (41) of the stop piece (40) has a width or height dimension which is greater than another width or height dimension of the second wall (42), the dimensions being taken in a plane transverse to the bonding surface (43).

4. Assembly according to any one of claims 1 to 3, characterized in that the first wall (41) is configured to extend partly over an upstream face of the rotor disk (20).

5. Assembly according to any one of claims 1 to 4, characterized in that the first wall (41) of the stop piece (40) extends perpendicularly on either side of the connecting surface (43).

6. Assembly according to any one of claims 1 to 5, characterized in that the second wall (42) of the stop piece (40) extends perpendicularly to the connecting surface (43) so as to be able to cover a downstream face of a blade foot.

7. Assembly according to claim 1, characterized in that the disc comprises a cavity hollowed out in the disc and in that the first wall (41) comprises a hook (44) mounted by interlocking in the cavity.

8. Assembly according to claim 1, characterized in that it further comprises a retaining ring (60) housed in a groove (23) of the rotor disc, at an internal end of the retaining ring (50), the retaining ring being configured to secure the retaining ring (50) to the disc (20) after mounting the retaining ring (50) on the disc.

9. A method for mounting the moving blades (10) of a low-pressure turbine in the recesses (21) of a rotor disk of said turbine, characterized in that it comprises, for each moving blade, the following steps: - installation of a stop piece (40) of the assembly according to any one of claims 1 to 6 against a radially internal end face (11c) of a blade foot (11), and - installation of the movable blade (10) equipped with the stop piece (40) in a cavity (21) of the rotor disc.

10. A method according to claims 11 and 12, characterized in that it further comprises the following steps: - installation of a retaining ring (60) in a groove (23) of the rotor disc, and - installation of a retaining ring (50) on the disc (20) along the first walls (41) of the stop piece (40), the retaining ring (50) being held in position by a locking made by the stop ring (60).

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