Device for axially retaining moving blade of low-pressure turbine in slot of rotor disc of low-pressure turbine and method for assembling said moving blade

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 slot (21) of a rotor disc of an axis (X) of the turbine. The device comprises a stop (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 (40) comprising:-a first wall (41) forming an end stop for the upstream face (11a) of the blade root (11); -a second wall (42) forming an end stop for the downstream face (11b) of the blade root (11); and-a connecting surface (43) intended to extend between the first and second walls (41, 42) along a radially inner end face (11c) of the blade root (11). Other features of the invention relate to a turbomachine rotor assembly and a method for assembling moving blades (10) in slots (21) of an LP turbine rotor disc.

Description

Technical Field

[0001] The invention relates to a device for axially retaining moving blades of a low-pressure (LP) turbine in slots of a rotor disk of the LP turbine. The invention also relates to a method for mounting these moving blades in a rotor disk.

[0002] The invention is applicable to the field of aviation, in particular to the field of low-pressure turbines for aircraft turbomachines. Background Art

[0003] In a known manner, a low pressure (LP) turbine comprises several consecutive impellers separated by distributor stages. The impeller, also called wheel, comprises so-called "moving" blades and a rotor disk. The outer periphery of the rotor disk comprises mounting grooves (called slots) extending substantially in the axial direction (i.e. at an angle of a few degrees relative to the axial direction). Each slot is designed to receive the root of a moving blade press-fitted into the slot.

[0004] Typically, a first axial retaining ring or flange arranged on the upstream face of a disk of the turbine and a second axial retaining ring arranged on the downstream face of the disk of the turbine are provided. These rings form axial stops for the blade roots received in the slots. Figure 1 An example of a low-pressure turbine section comprising three impellers 1a, 1b, 1c according to the prior art is shown. The impellers 1a, 1b, 1c are separated from each other by distributors 7, 8, each of which is equipped with a shroud 9, 10 forming an inner wall of the flow stream F. Each impeller 1a, 1b, 1c comprises a disk that rotates around a central axis of the turbine (indicated by the axis X) and comprises a peripheral rim 2a, 2b, 2c to which the blades are attached by their roots 3a, 3b, 3c. In particular, the first wheel 1a comprises a moving blade 4a, which is axially mounted by its root 3a in a slot 6a of the rim 2a of the disk. The root 3a of the blade 4a is axially blocked 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 snap rings that enable the root 3a, 3b, 3c of the blade 4a, 4b, 4c to be axially retained should be retained along the blade. In some cases, the axial retention of the flange or snap ring is ensured by a relatively complex-shaped docking hook or hook. In other cases, the axial retention is achieved by an engaging lock.

[0006] Nowadays, moving blades are usually made of ceramic matrix composite (CMC) materials, which have the advantage of being lightweight. CMC blades are therefore lighter than conventional metal blades. However, the manufacture of CMC blades with hooks is complicated, since this involves weaving and requires forming two layers of texture on the blade, at the platforms 5a, 5b, 5c located between the blade and the root 3a, 3b, 3c of the blade, one of which forms the surface that delimits the airflow and the hook, while the other serves to prevent the blade from tilting and covers the blade downstream. In addition, the centrifugal force transmitted from the axial flange or the snap ring to the hook integrated into the blade results in centrifugal mechanical loads, which are harmful for hooks made of CMC material.

[0007] In case of an engaged lock, the seal of the impeller must be pushed into the root of the low pressure distributor (LPD), which means that there is not enough space to integrate an axial stop solution at the back of the blade, ie on the downstream face of the blade root.

[0008] Therefore, there is a real need for a means for retaining the blade roots axially in the slots of the disk that does not require the fabrication of CMC hooks or seal advancement at the low pressure distributor root. Summary of the invention

[0009] In response to the problem discussed above of axially retaining the root of a moving blade in a slot of a disk, the applicant has provided a stopper positioned between the root of the blade and the bottom of the slot of the disk and extending between the upstream and downstream faces of the blade root.

[0010] In the following description, the terms "upstream" and "downstream" are defined relative to the air flow direction from the air inlet of the LP turbine to the air outlet of the LP turbine. In other words, upstream and downstream are understood to be along the central axis X relative to the general direction of the working gas.

[0011] In this specification, the term "external" refers to the surface or part of the component farthest from the central axis X of the turbine machine airflow (i.e., the rotation axis of the fan blades). The term "external" is contrary to the term "inner", which refers to the surface and part of the component closest to the central axis X.

[0012] According to a first aspect, the invention relates to a device for axially retaining a moving blade of a low-pressure turbine in a slot of a rotor disk having the axis of the turbine, characterized in that the device comprises a stop extending between an upstream face of a blade root of a moving blade and a downstream face of the blade root of the moving blade, the stop comprising:

[0013] - a first wall forming a stop for the upstream face of the blade root,

[0014] - a second wall forming a stop for the downstream face of the blade root, and

[0015] - a connecting surface extending between the first wall and the second wall along the radially inner end face of the blade root.

[0016] This device enables the blade root to be axially stopped or blocked in the slot of the disk without requiring any hooks on the blade or any specific parts on the downstream face of the impeller. This therefore avoids the need for an axial retaining ring, the centrifugal force of which must be transmitted to the hooks integrated in the CMC blade. In addition, this device has the advantage of an overall space reduction, saving space downstream of the blade root, leaving room for axial sealing.

[0017] In addition to the features just discussed in the preceding paragraph, the axial retaining device according to one aspect of the present invention may have one or more of the following additional features, which may be considered individually or in any technically possible combination:

[0018] - The stop is a one-piece metal part.

[0019] The first wall of the stopper has a width or height dimension that is greater than another width or height dimension of the second wall, these dimensions being taken in a plane transverse to the connection surface.

[0020] - The first wall is configured to extend partially over the upstream face of the rotor disk.

[0021] The first wall of the stopper extends vertically on both sides of the connection surface.

[0022] The second wall of the stop extends perpendicularly to the connecting surface so that the second wall can cover the downstream face of the blade root.

[0023] A second aspect of the invention relates to a turbomachine rotor assembly comprising a rotor disk having an axis X, the rotor disk having slots hollowed out at the periphery of the disk, the moving blades being mounted in the slots of the disk, two circumferentially adjacent slots around the disk each defining a tooth on the disk, characterised in that the assembly comprises:

[0024] - a plurality of stops as described above, each stop being used to retain a moving blade axially in a corresponding slot in the disk, and

[0025] - means for blocking the stopper against the disc,

[0026] The first wall of each stopper extends circumferentially to contact at least one upstream face of a tooth of the rotor disk.

[0027] Advantageously, the assembly may have the following features, which may be considered individually or in any technically possible combination:

[0028] - The tray comprises a cavity hollowed out in the tray, and the first wall comprises hooks interlockingly fitting into the cavity.

[0029] The assembly comprises a plurality of stops each arranged in a slot of the disc and configured such that the first walls of the plurality of stops are arranged circumferentially around the axis X, end to end.

[0030] The assembly comprises a retaining ring attached to the disk and mounted over the entire circumference of the rotor disk against the first wall of the stopper in order to retain the stopper in place in the slot of the disk.

[0031] The assembly further comprises a snap ring received in a groove of the rotor disk at the inner end of the retaining ring, the snap ring being configured to secure the retaining ring to the disk after the retaining ring has been mounted to the disk.

[0032] A third aspect of the invention relates to a method for mounting a moving blade of a low-pressure turbine in a slot in a rotor disk of the turbine, characterized in that, for each moving blade, the method comprises the following steps:

[0033] - installing the aforementioned stop against the radially inner end face of the blade root, and

[0034] - The moving blades equipped with the stop are mounted in the slots of the rotor disk.

[0035] The advantage of this approach is that it is relatively simple to implement.

[0036] Advantageously, the method comprises the following operations:

[0037] - installing a snap ring in a groove of the rotor disk, and

[0038] - Mounting a retaining ring on the disc along the first wall of the stopper, the retaining ring being held in place by the stop formed by the snap ring. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other advantages and features of the present invention will become apparent from a reading of the following description illustrated by the accompanying drawings, in which:

[0040] Already described Figure 1 shows a schematic longitudinal cross-sectional view of a portion of a LP turbine having several impellers according to the prior art;

[0041] Figure 2shows a longitudinal cross-sectional view of an axial retaining device according to the invention, wherein a stopper is mounted between the blade root and the slot of the disk;

[0042] Figure 3 A schematic upstream view and a schematic downstream view show a stop of an axial retaining device according to the invention, which stop is mounted between a blade root and a slot of a disk;

[0043] Figure 4 Several cross-sectional views from upstream to downstream showing various embodiments of the stopper according to the invention;

[0044] Figure 5A , Figure 5B and Figure 5C A sectional perspective view, an upstream view and a downstream view of an embodiment of an axial retaining device according to the present invention are respectively shown;

[0045] Figure 6 Several steps of the method for mounting a moving blade according to the invention are shown in perspective view; and

[0046] Figure 7 A perspective view is shown of several moving blades mounted in a rotor disk using axial retaining means according to the invention. DETAILED DESCRIPTION

[0047] An exemplary embodiment of an axial retaining device for a LP turbine blade is described in detail below with reference to the accompanying drawings. This example illustrates the features and advantages of the present invention. However, it should be noted that the present invention is not limited to this example.

[0048] In the drawings, identical elements are identified by identical reference numerals. For reasons of readability, the size ratios between the illustrated elements are not taken into account.

[0049] exist Figure 2 An example of an axial retaining device according to the invention is shown in a cross-sectional view in FIG. For each moving blade 10, the axial retaining device 30 comprises a stopper 40 configured to be housed between the root 11 of the blade 10 and the slot 21 of the disk 20 of the rotor of the LP turbine. The stopper 40 extends between the upstream face 11a of the blade root 11 and the downstream face 11b of the blade root. To this end, the stopper 40 comprises:

[0050] a first wall 41 (also called upstream wall) configured to be positioned at least partially along the upstream face 11 a of the blade root,

[0051] a second wall 42 (also called downstream wall) configured to be positioned at least partially along the downstream face 11 b of the blade root, and

[0052] A connecting surface 43 connecting the upstream wall 41 and the downstream wall 42 axially, ie along the central axis (X), this connecting surface 43 being along the inner face 11 c of the blade root.

[0053] The upstream and downstream walls of the stopper 40 may be made, for example, of a metal or alloy, such as one of the superalloys commonly used in this area of ​​the turbine. The upstream wall 41 and the downstream wall 42 are, for example, square or rectangular in shape. The connecting surface 43 may be a plate, preferably made of the same metal or alloy as the upstream and downstream walls. The connecting surface 43 is preferably rectangular, the axial dimension of which is substantially greater than the axial dimension of the blade root 11. The upstream and downstream walls 41, 42 and the connecting surface 43 may be made in a single piece, so that the stopper 40 is one-piece.

[0054] According to some embodiments, the upstream wall 41 and the downstream wall 42 of the stopper have similar dimensions. According to other embodiments, the upstream wall 41 and the downstream wall 42 have different dimensions, wherein the dimensions of the upstream wall 41 are greater than those of the downstream wall 42. Figure 2 and Figure 3 As shown in the example of , the upstream wall 41 may extend radially (i.e., along an axis perpendicular to the axis X) in front of the upstream face 11a of the blade root and in front of a portion of the upstream face of the disk 20 below the slot. Thus, the upstream wall 41 may extend parallel to the upstream opening 21a of the slot 21 and to the inner portion of the upstream face of the disk 20 (the inner portion being the portion of the disk without the inter-slot teeth 22). In this example, the downstream wall 42 extends radially in front of the downstream opening 21b of the slot 21, i.e., along the downstream face 11b of the blade root. Figure 2 and Figure 3 In the example shown, the stop 40 thus has an inverted T-shaped cross section, wherein the upstream wall 41 extends radially on both sides of the connecting surface 43, while the downstream wall 42 extends radially in the direction of the platform 12 of the blade 10. With this configuration, the upstream wall 41 is blocked upstream by the disk 20, so that the entire stop 40 is axially blocked upstream.

[0055] In addition to the stopper 40, the axial retaining means 30 of the invention may comprise a flange 50 or a retaining ring mounted radially along the upstream face 20a of the disk 20. This flange 50, which is annular in shape, extends parallel to the slots 21 and the inter-slot teeth 22 of the disk 20 over the entire circumferential length of the disk. This flange 50 is generally shaped as a flange of an LP turbine and comprises a hook 51 which is partially housed in the groove 23 of the disk 20. This hook 51 ensures that the flange 50 is hooked on the disk 20. Thus, the flange 50 mounted along the disk 20 extends upstream of the upstream wall 41 of the stopper 40 so as to prevent any axial movement of the stopper 40 from downstream to upstream.

[0056] It can therefore be understood that the stopper 40 is axially blocked in both directions, ie, from upstream to downstream and from downstream to upstream. Therefore, the blade root 11 itself located inside the stopper 40 is axially blocked in both directions.

[0057] According to some embodiments, the axial retaining means 30 further comprises an axial snap ring 60 housed in the groove 23 of the disk 20. The axial snap ring 60 is a generally annular piece made of a flexible, generally elastic material, such as a super alloy commonly used in turbines. The axial snap ring 60 comprises a radial groove extending over the entire cross section of the snap ring. The radial groove enables the axial snap ring to be lowered into the groove 23 to insert (or remove) the flange 50.

[0058] Figure 4 Embodiments in which the stopper 40 has different shapes are shown. Figure 4 Figure A in Figure 1 shows an example of a stopper 40 in a cross-sectional view, which includes an upstream wall 41 having a shoulder 44 inserted into the disk 20. This shoulder 44, also called a hook, is formed as an axial extension extending from the upstream wall 41 at a substantially right angle. This axial extension is designed to be inserted into a suitable housing 24 located at the entrance of the groove 23 of the disk 20. In the cross-sectional view, the shoulder 44 is hook-shaped, a part of which is accommodated in the disk 20. In other words, the shoulder 44 is inserted into the disk below the slot 21 receiving the stopper 40, thereby partially interlocking with the inner periphery of the slot 21 of the disk 20, so that the centrifugal force of the stopper 40 is transmitted to the disk, and the blade 10 partially releases this force.

[0059] Figure 4 Figures B and C of show an example of a stopper 40 in a cross-sectional view and a schematic upstream view, respectively, in which an upstream wall 41 extends radially to the platform 12 of the blade 10 so as to form a partial seal for the slot 21. In this embodiment, the stopper 40 has a generally U-shaped cross section, in which the upstream wall 41 extends in a single radial direction from the connecting surface 43; the upstream wall 41 extends radially further than the downstream wall 42 until it reaches the blade platform 12. In this embodiment, the axial blocking or stopping in the downstream direction is achieved by blocking the upstream wall 41 against the teeth 22 of the disk 20.

[0060] Figure 4 Figure D in Figure 4 shows an example of a stop 40 in a schematic downstream view, in which a downstream wall 42 extends radially on both sides 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 disk 20 below the slot 21. The downstream wall 42 thus participates in axially blocking the stop 40 in the upstream direction.

[0061] Of course, the various exemplary embodiments described above may be combined with each other, for example, the upstream wall 41 of Figure C is combined with the downstream wall 42 of Figure D, or the upstream wall having the shoulder 44 of Figure A is combined with the downstream wall 42 of Figure D, and so on.

[0062] Figure 4 The embodiment of Figure B in Figure 5A In the cross-sectional perspective view, Figure 5B In the upstream view (or front view), Figure 5C These views show a stopper 40 having a generally U-shaped cross section, which is mounted in the slot 21 of the disk 20 below the blade root 11 so as to cover the upstream face 11a of the blade root 11, the downstream face 11b of the blade root and the inner face 11c of the blade root. Figure 5A Also shown is a groove 23 in the disc 20 in which a snap ring 60 and a flange 50 are received, the snap ring 60 being located at the inner end of the flange 50 .

[0063] Regardless of the shape and size of the upstream and downstream walls of the stopper 40, the axial retaining means 30 is Figure 6 The installation method according to the present invention comprises the following steps shown in Figures E to H:

[0064] - Figure E: production of a stopper 40 , wherein the upstream wall 41 and the downstream wall 42 of the stopper 40 are connected by a connecting surface 43 ;

[0065] - Figure F: The stopper 40 is mounted below the blade root 11 , ie against the inner face 11 c of the blade root 11 of the blade 10 ;

[0066] - Diagram G: Installation of a moving blade 10 equipped with a stop 40 into a slot 21 in a disk 20, the upstream wall 41 of the stop being in contact with the

[0067] The teeth 22 on both sides of the slot 21 are in contact; and

[0068] Diagram H (for the embodiment in question, after all the blades have been installed): flange 50 is installed along upstream wall 41 in groove 23 of disk 20 , after collar 60 has been positioned in groove 23 .

[0069] Once all the moving blades 10, each equipped with a stop 40, have been mounted in the slots 21 of the disk 20, the upstream walls 41 of all the stops 40 are positioned circumferentially side by side, one behind the other. Figure 7 An example of several upstream walls 41 arranged side by side is shown in FIG. Figure 7Only two blade roots 11 are shown in FIG. 1 , but several upstream walls 41 are shown side by side, each forming part of one of the stops 40 housed in the slots 21 of the disk 20 . Figure 7 Also shown is a flange 50 which is mounted along the upstream wall 41 and which forms an axial retainer of the stop 40 (from downstream to upstream) and therefore of the blade root 11. The flange 50 not only ensures the axial retention of the blade root 11 by the stop 40, but also ensures ventilation of the slots 21 of the disk. Indeed, ventilation of the slots 21 of the disk 20 is essential during operation of the turbine, given the high temperatures of the gases circulating in the flow stream of an LP turbine.

[0070] Although described through multiple examples, alternatives and embodiments, the axial retaining device according to the present invention includes various alternatives, modifications and improvements, which will be obvious to those skilled in the art and should be understood to be within the scope of the present invention.

Claims

1. A turbomachine rotor assembly, comprising a rotor disk (20) and moving blades (10), the rotor disk having an axis (X), the rotor disk having slots (21) hollowed out at the periphery of the rotor disk, the moving blades being mounted in the slots (21) of the disk, two circumferentially adjacent slots around the disk each defining a tooth of the disk, characterized in that The assembly comprises a plurality of stoppers (40) extending 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 stoppers (40) comprising: - a first wall (41) forming a stop for the upstream face (11a) of the blade root (11), - a second wall (42) forming a stop for the downstream face (11b) of the blade root (11), and a connecting surface (43) extending between the first wall (41) and the second wall (42) along the radially inner end face (11c) of the blade root (11), - each stopper (40) is used to axially retain the moving blade (10) in a corresponding slot of the disk (20), and - means (50, 60) for blocking said stopper against said disk (20), - said first wall (41) of each stopper (40) extends circumferentially so as to come into contact with at least one upstream face of a tooth (22) of said rotor disk, - a plurality of stops (40) each disposed in a slot (21) of the disk (20) and configured such that the first walls (41) of the plurality of stops (40) are arranged circumferentially end to end around the axis (X), A retaining ring (50) is attached to the disk and is mounted over the entire circumference of the rotor disk (20) against the first wall (41) of the stopper (40) to hold the stopper (40) in place in the slot of the disk.

2. The assembly according to claim 1, characterized in that The stopper (40) is a one-piece metal part.

3. The assembly according to claim 1 or 2, characterized in that The first wall (41) of the stopper (40) has a width or height dimension that is greater than another width or height dimension of the second wall (42), said dimension being taken in a plane transverse to the connecting surface (43).

4. The assembly according to any one of claims 1 to 3, characterized in that The first wall (41) is configured to extend partially on the upstream face of the rotor disk (20).

5. The assembly according to any one of claims 1 to 4, characterized in that The first wall (41) of the stopper (40) extends vertically on both sides of the connecting surface (43).

6. The assembly according to any one of claims 1 to 5, characterized in that The second wall (42) of the stopper (40) extends perpendicularly to the connecting surface (43) so as to be able to cover the downstream face of the blade root.

7. The assembly according to claim 1, characterized in that The tray includes a cavity hollowed out therein, and the first wall (41) includes a hook (44) interlockingly fitted into the cavity.

8. The assembly according to claim 1, characterized in that The assembly also includes a snap ring (60) received in a groove (23) of the rotor disk at an inner end of the retaining ring (50), the snap ring being configured to secure the retaining ring (50) to the disk (20) after the retaining ring (50) has been mounted to the disk.

9. A method for mounting a moving blade (10) of a low-pressure turbine in a slot (21) of a rotor disk of said turbine, characterized in that For each moving blade, the method comprises the following steps: - mounting a stopper (40) of an assembly according to any one of claims 1 to 6 against a radially inner end face (11c) of a blade root (11), and - Mounting the moving blade (10) equipped with the stop (40) in the slot (21) of the rotor disk.

10. The method according to claims 11 and 12, characterized in that The method further comprises the following steps: - installing a snap ring (60) in the groove (23) of the rotor disk, and - Mounting a retaining ring (50) on said disc (20) along said first wall (41) of said stopper (40), said retaining ring (50) being held in place by the stop formed by said snap ring (60).

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