FR3102152A1 - improved attachment of counter-rotating turbine blades - Google Patents

Abstract

Improved attachment of counter-rotating turbine blades Counter-rotating turbine (C) of a turbomachine (10) comprising an inner rotor and an outer rotor having an outer drum (50b) to which are fixed a plurality of outer movable wheels each comprising outer movable vanes, the outer rotor comprising a downstream movable wheel (60) comprising a plurality of downstream movable vanes (600), each vane (600) comprising at least one downstream movable vane (61), a radially outer end of at least one vane ( 600) being fixed to the outer drum (50b) downstream of said outer drum by means of at least one first axial fixing means (71), and a radially inner end of said at least one blade (600) being fixed to a internal disc (25), by means of at least one second axial fixing means (72), the blade (600) being a separate part from the external drum (50b) and from the internal disc (25). Figure for the abstract: Fig. 3.

Description

improved attachment of contra-rotating turbine blades

This presentation relates to the field of turbomachines. More specifically, the present disclosure relates to a counter-rotating turbomachine turbine, and a turbomachine comprising such a turbine.

An aircraft turbomachine extends around an axis and generally comprises, from upstream to downstream in the direction of gas flow along this axis, a fan, a low pressure compressor, a high pressure compressor, a combustion chamber, a high pressure turbine and a low pressure turbine. The low pressure compressor rotor is driven by the low pressure turbine rotor, and the high pressure compressor rotor is driven by the high pressure turbine rotor.

In order to improve engine efficiency, aircraft turbomachines can be equipped with a counter-rotating low-pressure turbine. The counter-rotating turbine comprises an inner rotor, called a fast rotor, connected to a first turbine shaft, and configured to rotate in a first direction of rotation, and an outer rotor, called a slow rotor, connected to a second turbine shaft, and configured to rotate coaxially with the inner rotor and in a second direction of rotation, opposite to the first direction of rotation. The vanes of the first rotor are alternated with the vanes of the second rotor in the axial direction. The blades of each stage of the inner rotor are fixed to a disc, or internal drum integral with the first turbine shaft and rotating in the first direction of rotation, and the blades of each stage of the outer rotor are fixed to a disc, or external drum secured to the second turbine shaft and rotating in the second direction of rotation.

In known manner, the connection between the outer drum of the outer rotor, and the second turbine shaft, is achieved by means of a rotating casing, or downstream movable wheel, fixed to the outer drum downstream of the latter. More specifically, the rotating casing comprises an outer radial shroud fixed to the outer drum axially downstream of the latter, and an inner radial shroud, or inner disc, integral with the second turbine shaft. Vanes extend radially between the inner shroud and the outer shroud, and make it possible to keep the latter fixed to one another, the rotation of one causing the rotation of the other. Thus, when the blades of the outer rotor are driven in rotation in the second direction of rotation, the rotation of the outer drum causes the rotation of the outer shroud.

The outer shroud, the inner disc, and the blades extending between them, form a single part, the rotating casing thus being manufactured in one piece. However, although this one-piece structure allows precise centering of the outer rotor with respect to the inner rotor, it promotes the propagation of cracks, or splits, forming on the blades of the casing rotating in the hot air flow path, up to to critical parts of the outer rotor, including the inner disc and outer shroud. Such cracks may be due to objects being ingested into the engine, hitting one or more blades.

There is therefore a need for a counter-rotating turbine architecture making it possible to overcome at least in part the above drawbacks.

This presentation relates to a counter-rotating turbomachine turbine extending around an axis of rotation and comprising:
- an internal rotor configured to rotate around the axis of rotation, and comprising an internal drum on which is fixed a plurality of internal mobile wheels, each comprising internal mobile blades, and being supported in rotation by a first shaft,
- an external rotor configured to rotate around the axis of rotation in a direction opposite to the direction of rotation of the internal rotor, and comprising an external drum on which is fixed a plurality of external mobile wheels each comprising external mobile blades, and being supported in rotation by a second shaft coaxial with the first shaft, the outer rotor comprising at least one downstream mobile blade, the blade comprising at least one downstream mobile blade,
a radially outer end of at least one blading being fixed to the outer drum downstream of said outer drum via at least one first axial fixing means, and a radially inner end of the blading being fixed to an inner disc integral with the second shaft, via at least one second axial fixing means, the blade being a separate part of the outer drum and of the inner disc.

In certain embodiments, the first and the second axial fixing means extend mainly according to the axis of rotation.

In this discussion, the terms "inner" and "outer", and the terms "inner" and "outer" and their derivatives are considered in the radial direction of the turbine. Similarly, the terms "upstream" and "downstream" are considered according to the direction of gas flow in the turbomachine, along the axis of rotation.

The first and the second shaft can be tubular, and are coaxial, getting along along the axis of rotation. The internal mobile wheels of the internal rotor are alternated, according to the axial direction, with the external mobile wheels of the external rotor. The downstream movable wheel forms a rotating casing fixed to the outer drum downstream of the latter, and rotating at the same time as the latter. The downstream mobile wheel makes it possible to make the connection between the external drum and the second shaft, thus making it possible to transmit the torque of the external mobile wheels to the second shaft.

It is further understood by "axial fixing means" that the contact between the ends of the blade and the outer drum and the inner disc respectively takes place mainly in an axial direction, that is to say substantially parallel to the axis of rotation of the turbine. In other words, the contact surface between these different parts is substantially perpendicular to the axis of rotation of the turbine. This configuration allows axial tightening between these different parts, limiting the risks of variations in tightening due to centrifugal forces, resulting in an off-centering of the outer rotor with respect to the inner rotor.

Furthermore, according to this configuration, the blading(s) do not form a single and same part with the internal disc in a single piece, but are separate parts, fixed to each other via the second axial fixing means. Thus, when a crack appears on one or more blades of the blading, the risks of propagation of this crack as far as the critical parts of the outer rotor such as the outer drum and the inner disc are limited, or even eliminated. , by the presence of the first and second axial fixing means, and of the interfaces between these various parts. This device thus makes it possible to ensure precise centering of the outer rotor with respect to the inner rotor, while limiting the propagation of cracks in a blade, up to the critical parts.

In certain embodiments, the first and the second axial fixing means are bolted connections.

The use of bolted connections allows the blades to be clamped effectively against the internal disc and the external drum. Thus, during the transmission of the torque from the external rotor to the internal disc, the shearing stresses undergone by the bolted connections will be limited, compared to the use of pins, for example, on which the shearing stresses cause fatigue and rapid wear of these. In addition, wear phenomena due to friction between the surfaces of the internal disc, the external drum, and the blades under the effect of movements potentially caused by insufficient tightening, are limited by the firm fixing provided by the bolted connections.

In some embodiments, the outer end of the blade includes an outer platform and a first radial flange extending radially outwardly of the turbine from the outer platform, and being attached to the outer drum through the first axial fixing means.

The outer platform is attached to the radially outer end of the downstream moving blade(s) so as to form a single piece with the latter. The platforms and the blades can in particular be manufactured in one piece. The platforms make it possible to delimit the hot air flow vein. The first radial flange extends from the outer platform to the outside of the turbine in the radial direction, perpendicular to the axis of rotation of the turbine. It also forms a single piece with the outer platform, and has an axisymmetric shape. It has a flat face in contact with a flat face of a radial flange arranged at the downstream end of the outer drum. Preferably, the first radial flange comprises at least one orifice allowing attachment to the outer drum via the first axial attachment means. The orifice is preferably circular. This method of fixing between two radial flanges by means of the axial fixing means, in particular a bolted connection, has the advantage of being simple to implement.

In some embodiments, the inner end of the blading includes an inner platform and a second radial flange extending radially inwardly of the turbine from the inner platform, and being attached to the inner disc through the second axial fixing means.

Preferably, each blade extends between two respective platforms, an internal platform and an external platform. These platforms make it possible to delimit the hot air flow vein. The internal platform is fixed to the radially internal end of the downstream moving blade(s) so as to form one and the same part with the latter, and also with the external platform. The second radial flange extends from the internal platform towards the inside of the turbine in the radial direction, perpendicular to the axis of rotation of the turbine. It preferably also forms one and the same piece with the internal platform. It has a flat face in contact with a flat face of a radially outer end of the internal disc. Preferably, the second radial flange comprises at least one orifice allowing attachment to the internal disc via the second axial attachment means. The orifice is preferably circular. This method of fixing between two radial flanges by means of the axial fixing means, in particular a bolted connection, also has the advantage of being simple to implement.

In certain embodiments, at least one of the first and of the second axial fixing means comprises a means for tangential centering of the blading with respect to the outer drum.

The tangential centering means can be a cylindrical pin inserted in an orifice of a radial flange, or cylindrical rings surrounding the bolted connection, and whose dimensions make it possible to eliminate the clearances existing between the walls of the orifice and the bolted connection. . The movements of the blades of the downstream mobile blades in the circumferential direction, around the axis of rotation of the turbine, are thus limited.

In some embodiments, in the radial direction, the length of the second radial flange is less than half the distance between the internal platform and the external platform.

In other words, the second radial flange extends towards the inside of the turbine, up to its attachment to the internal disk, over a distance less than half the length of a downstream moving blade. Limiting the length of this second radial flange makes it possible to further limit the propagation of cracks forming on one or more downstream moving blades, in the hot air stream.

In some embodiments, the first radial flange is attached to the outer drum via at least two first axial attachment means.

This improves the attachment between the first radial flange and the outer drum, and resists shearing stresses more effectively.

In certain embodiments, the turbine comprises a plurality of downstream mobile blades, each downstream mobile blade comprising an external attachment platform fixed to the external drum via at least one first axial attachment means, and an internal fixing fixed to the internal disc via at least one second axial fixing means.

Thus, whatever the downstream mobile blade undergoing a crack, the propagation of this crack will be limited by the presence of a first or a second fastening means.

In some embodiments, each blading comprises a single downstream moving vane.

Thus, when a single downstream moving blade has a crack, only this blade will need to be replaced, freeing it from its first and second means of axial attachment to the outer drum and to the inner disc respectively. Thus, the propagation of the crack will be limited to this single blade, and will not reach the external drum, the internal disc or another moving blade downstream.

This presentation also relates to a turbomachine comprising a counter-rotating turbine according to any one of the preceding embodiments.

The invention and its advantages will be better understood on reading the detailed description given below of various embodiments of the invention given by way of non-limiting examples. This description refers to the attached figure pages, on which:

FIG. 1 represents a general view illustrating the principle of operation of a turbine engine with counter-rotating fans,

FIG. 2 represents a perspective view of a moving blade downstream comprising a single blade, according to the present presentation,

Figure 3 shows a side view of the blade of Figure 2, attached to an outer drum and an inner disc,

Figure 4 shows a perspective view of an assembly of blades of Figure 2, fixed to the outer drum and to the inner disc,

Figure 5 shows a detailed view of the attachment of a blade of Figure 4 on the outer drum.

Referring to Figure 1, a turbine engine 10 with counter-rotating fans has a longitudinal axis X-X. From upstream to downstream in the direction of gas flow in the turbomachine (represented by the black arrow), the turbomachine 10 essentially comprises three parts: an upstream module A (or fan section), an intermediate module B (or body high pressure) and a downstream module C (or low pressure turbine section). Further, the terms "internal" or "external" and their derivatives refer to the radial direction of the turbomachine, the radial direction being perpendicular to the X-X axis.

The three parts A, B and C of the turbomachine are modular, that is to say they each form a single assembly and can each be replaced by being separated from the other parts of the turbomachine.

In a manner well known per se, the high-pressure body B comprises a gas generator to produce combustion gases. This gas generator comprises a compressor 12, a combustion chamber 14 and a high-pressure turbine 16.

The air compressed by the compressor 12 is mixed with the fuel in the combustion chamber 14 before being burned there. The combustion gases thus produced drive the moving blades of the high-pressure turbine 16 which itself drives the compressor 12 via a high-pressure shaft 18. The circulation of the combustion gases in the turbomachine 10 takes place axially from upstream to downstream.

The fan section A is located upstream of the turbomachine 10. A cowl 28 annularly surrounds this fan section A. The cowl 28 is supported by spacers 30 which extend radially towards the inside of the turbomachine .

Fan section A comprises a first row of fan blades 32 mounted on an upstream fan shaft 34 which is connected to an upstream end of the second low-pressure shaft 24.

Fan section A also includes a second row of fan blades 36 which are spaced axially downstream from the first row of fan blades 32 and mounted on an aft fan shaft 38 connected to an upstream end of the first low-pressure shaft 26.

The first and second rows of fan blades 32, 36 thus rotate in opposite directions which are represented, by way of example, by the respective arrows F1 and F2. This contra-rotating fan configuration thus gives the turbomachine high efficiency for relatively low specific consumption.

The fan blades 32, 36 extend radially from the upstream 34 and downstream 38 fan shafts practically as far as the cowl 28. They are arranged in the air circulation passage supplying both the primary stream 40 leading to the compressor 12 of the high pressure body B and the secondary vein 42 bypass.

At its upstream end, the second low-pressure shaft 24 supports the first low-pressure shaft 26 in rotation via a first rolling bearing 44 and a second rolling bearing 46 disposed downstream of the first .

The first rolling bearing 44 is of the ball type to withstand the axial loads, while the second rolling bearing 46 is of the roller type to withstand the radial loads of the turbomachine.

The low-pressure turbine section C comprises a first annular rotor, or external rotor. This first rotor comprises a row of internal impellers comprising external impeller impellers 20 which extend radially inwards and which are spaced axially from one another.

The low-pressure turbine section C also includes a second annular rotor, or internal rotor. This second rotor comprises a row of internal impellers comprising internal impeller blades 22 which extend radially outward and which are spaced axially from each other. The turbine blades 20, 22 of the first and second rotors are arranged alternately with respect to each other so that the first and the second rotors are nested one inside the other.

The external mobile wheels of the external rotor are supported in rotation by the second low-pressure shaft 24. Similarly, the internal mobile wheels of the internal rotor are supported in rotation by the first low-pressure shaft 26 disposed coaxially around the second shaft 24. The low-pressure shafts 24, 26 extend axially from upstream to downstream of the turbomachine.

The low-pressure turbine section C is traversed by the combustion gases coming from the high-pressure body B. These combustion gases therefore rotate the turbine blades 20, 22 of the first and second rotors in opposite directions. Thus, the first and second low-pressure shafts 24, 26 also rotate counter-rotatingly.

Furthermore, the internal mobile blades 22 comprise a foot fixed to an axisymmetric internal drum 50a, and extend radially outwards from this foot to a radially outer end. The outer moving blades 20 comprise an outer portion fixed to an axisymmetric outer drum 50b, and extend radially inwards from this base to a radially inner end.

The remainder of the description describes a mode of attachment for moving blades downstream, with reference to the low pressure turbine C of the turbomachine 10. Nevertheless, this method of attachment is not limited to this low pressure turbine, and can be adapted to other elements of the turbomachine, for example the high pressure turbine.

The connection between the outer drum 50b of the outer rotor, and the second turbine shaft 24, is achieved by means of a rotating casing, or downstream movable wheel 60, fixed to the outer drum 50b downstream of the latter. More specifically, this downstream moving wheel 60 is the moving wheel arranged furthest downstream in the outer rotor. It may be in particular, in a known manner, stage number six of the counter-rotating turbine. This downstream movable wheel 60 comprises a radially outer shroud 62 fixed to the outer drum 50b axially downstream of the latter, and a radially inner shroud 63 secured to the second turbine shaft 24, by means of an axisymmetric internal disk 25 s extending between the inner shroud 63 and the second turbine shaft 24.

The inner 63 and outer 62 shrouds are concentric and axisymmetric around the X axis. Radial arms, called downstream moving vanes 61, extend radially between the inner shroud 63 and the outer shroud 62, and allow the latter to be held together each other, the rotation of one causing the rotation of the other. Thus, when the blades 20 of the outer rotor are driven in rotation in the second direction of rotation, the rotation of the outer drum 50b causes the rotation of the outer shroud 62. This rotational movement is transmitted to the inner shroud 63 and to the inner disc 25 through the blades 61 of the rotating casing, allowing the rotation of the second turbine shaft 24.

More specifically, the downstream moving wheel 60 comprises a plurality of downstream moving blades 600 assembled to each other circumferentially to form the downstream moving wheel 60 which is annular. Each downstream mobile blade 600 comprises between one and six downstream mobile blades 61. In the example described below with reference to FIGS. 2 to 4, the blades 600 comprise a single blade 61. This example is not limiting, the invention being applicable to blades comprising a plurality of downstream moving blades 61.

In this example therefore, each blade 600, one of which is illustrated in perspective in FIG. 2, comprises a moving downstream blade 61 extending between a radially outer platform 620 and a radially inner platform 630. The circumferential assembly of the blades, and therefore these platforms 620, 630 to each other, form the outer 62 and inner 63 shrouds, the inner faces of which delimit the hot air flow path in which the downstream moving blades 61 are located.

The blading 600 comprises a first radial flange 621 extending radially towards the outside of the turbine from the upstream end of the external platform 620. The first radial flange 621 can comprise between one and ten axial orifices 622. In the example illustrated, the first radial flange 621 comprises three holes 622.

Furthermore, the blade 600 comprises a second radial flange 631 extending radially towards the inside of the turbine from a central region in the axial direction, for example, of the internal platform 630. The second radial flange 631 can comprise between one and ten axial orifices 632. In the example illustrated, the second radial flange 631 comprises a single orifice 632. In addition, the length of the second radial flange 631 is preferably less than half the length of the blade 61.

Each vane 600 is fixed both to the outer drum 50b and to the inner disc 25. In other words, each vane 600 is an individual part distinct from the outer drum 50b and from the inner disc 25, and attached to the outer drum 50b and to the internal disk 25.

More specifically, the first radial flange 621 is fixed to a radial flange 501b of the outer drum 50b, at a downstream end of the latter, by means of first axial fixing means. These first axial fixing means are bolted connections 71. Each bolted connection 71 comprises a threaded screw 710 and a nut 712. The threaded screw 710 is inserted into holes in the radial flange 501b of the outer drum 50b and in the corresponding holes 622 of the first radial flange 621, from the side of the outer drum 50b for example. The nut 712 is screwed onto the screw 710, on the side of the first radial flange 621, so as to tighten the first radial flange 621 against the radial flange 501b of the outer drum 50b. Each blade 600 is therefore fixed, at its radially outer end, to the outer drum 50b by three bolted connections 71.

In addition, the second radial flange 631 is fixed to an outer radial flange 251 of the internal disk 25, via a second axial fixing means. This second axial fixing means is a bolted connection 72. Each bolted connection 72 comprises a threaded screw 720 and a nut 722. The threaded screw 720 is inserted into a hole in the outer radial flange 251 of the inner disc 25, and into a hole 632 corresponding to the second radial flange 631, from the side of the internal disc 25 for example. The nut 722 is screwed onto the screw 720, on the side of the second radial flange 631, so as to tighten the second radial flange 631 against the external radial flange 251 of the internal disc 25. Each blade 600 is therefore fixed, at its end radially internal, to the internal disc 25 by a bolted connection 72.

According to this configuration, when a blade 61 has a crack, or fissure, caused for example by an object ingested in the hot air flow stream, the propagation of this crack will be limited to the single blade 600 comprising this blade 61. The propagation of this crack will indeed be stopped, at most, at the level of the bolted connections 71, 72, and will not propagate to the outer drum 50b and to the inner disc 25.

Furthermore, the bolted connections 71, 72 may include tangential centering means. These centering means may for example comprise a cylindrical pin 80, arranged, for example, in at least one orifice 622 of the three orifices 622 of the first radial flange 621. According to the example presented in FIG. 5, the first radial flange 621 is fixed to the radial flange 501b of the outer drum 50b by means of two bolted connections 71 inserted in the first and the third of the three orifices 622 of the first radial flange 621. The orifice 622 disposed at the center, between the first and the third orifice 622, is not crossed by a bolted connection 71, but by a cylindrical pin 80. The cylindrical pin 80 can be inserted by force into the orifice 622, and the corresponding orifice of the flange 501b of the outer drum 50b , making it possible to adjust the circumferential position of the blading 600, and thus its centering.

Although the present invention has been described with reference to specific embodiments, it is obvious that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the different illustrated/mentioned embodiments can be combined in additional embodiments. Accordingly, the description and the drawings should be considered in an illustrative rather than restrictive sense.

Claims (11)

Counter-rotating turbine (C) of turbomachine (10) extending around an axis of rotation (X) and comprising:
- an inner rotor configured to rotate around the axis of rotation (X), and comprising an inner drum (50a) on which is fixed a plurality of inner movable wheels (22), each comprising inner movable blades, and being supported in rotation by a first shaft (26),
- an outer rotor configured to rotate around the axis of rotation (X) in a direction opposite to the direction of rotation of the inner rotor, and comprising an outer drum (50b) on which is fixed a plurality of outer movable wheels (20) each comprising external mobile blades, and being supported in rotation by a second shaft (24) coaxial with the first shaft (26), the external rotor comprising a downstream mobile wheel (60) comprising at least one downstream mobile blade (600), the blading (600) comprising at least one downstream moving blade (61),
a radially outer end of at least one blade (600) being fixed to the outer drum (50b) downstream of said outer drum via at least one first axial fixing means (71), and a radially inner end of the blading (600) being fixed to an internal disk (25) integral with the second shaft (24), via at least one second axial fixing means (72), the blading (600) being a part separate from the outer drum (50b) and the inner disc (25). Turbine (C) according to Claim 1, in which the first and the second axial fixing means (71, 72) extend mainly along the axis of rotation (X).
Turbine (C) according to Claim 1 or 2, in which the first and the second axial fixing means (71, 72) are bolted connections. Turbine (C) according to any one of claims 1 to 3, in which the external end of the vane (600) comprises an external platform (620) and a first radial flange (621) extending radially towards the exterior of the turbine from the outer platform (620), and being fixed to the outer drum (50b) via the first axial fixing means (71). Turbine (C) according to any one of claims 1 to 4, in which the internal end of the blade (600) comprises an internal platform (630) and a second radial flange (631) extending radially towards the interior of the turbine from the internal platform (630), and being fixed to the internal disk (25) via the second axial fixing means (72). Turbine (C) according to any one of Claims 1 to 5, in which at least one of the first and of the second axial fixing means (71, 72) comprises a means for tangential centering of the blade (600) by relative to the outer drum (50b). Turbine (C) according to Claim 5 or 6, in which, in a radial direction, the length of the second radial flange (631) is less than half the distance between the internal platform (630) and the external platform (620 ). Turbine (C) according to any one of Claims 4 to 7, in which the first radial flange (621) is fixed to the outer drum (50b) via at least two first axial fixing means (71). Turbine (C) according to any one of claims 1 to 8, comprising a plurality of blades (600) movable downstream, each blade (600) movable downstream comprising an external platform (620) for fixing fixed to the external drum (50b) via at least one first axial fixing means (71), and an internal fixing platform (630) fixed to the internal disc (25) via at least one second axial fixing means (72 ). Turbine (C) according to any one of claims 1 to 9, in which each vane (600) comprises a single vane (61). A turbomachine (10) comprising a counter-rotating turbine (C) according to any preceding claim.