IMPROVED ARCHITECTURE OF A TURBOMACHINE WITH COUNTER-ROTATING TURBINE

Abstract

Counter-rotating turbine of a turbomachine extending about an axis of rotation and comprising an inner rotor rotating about the axis of rotation, and comprising at least one inner movable blade rotatably supported by a first shaft, an outer rotor rotating about the axis of rotation in a direction opposite to the inner rotor, and comprising at least one outer movable blade rotatably supported by a second shaft coaxial with the first shaft, the first and second shafts extending axially from upstream to downstream of the turbine, wherein the first shaft is guided in rotation by a first bearing disposed between the first shaft and an upstream casing of the turbine, and the second shaft is guided in rotation by a second bearing disposed between the second shaft and said upstream casing of the turbine.

Claims

1. A counter-rotating turbine of a turbomachine, extending about an axis of rotation and comprising: an inner rotor configured to rotate about the axis of rotation, and comprising at least one inner movable blade rotatably supported by a first shaft, an outer rotor configured to rotate about the axis of rotation in a direction opposite to the inner rotor, and comprising at least one outer movable blade rotatably supported by a second shaft coaxial with the first shaft, the first and second shafts extending axially from upstream to downstream of the turbine, wherein the first shaft is guided in rotation by a first bearing disposed between the first shaft and an upstream casing of the turbine, and the second shaft is guided in rotation by a second bearing disposed between the second shaft and said upstream casing of the turbine, the counter-rotating turbine comprising an outer casing at least partially surrounding the outer rotor, the outer casing extending axially from an upstream end of the turbine, over a length of less than 50% of the length of the turbine.

2. The turbine according to claim 1, wherein the at least one inner movable blade is rotatably supported by a portion of the first shaft cantilevered from the first bearing, and the at least one outer movable blade is rotatably supported by a portion of the second shaft cantilevered from the second bearing.

3. The turbine according to claim 1, wherein the second bearing is disposed between the second shaft and the first shaft.

4. The turbine according to claim 1, wherein the first and second bearings are disposed substantially in line with each other along the axis of rotation.

5. The turbine according to claim 1, wherein the first and second bearings are disposed substantially at a median plane of the turbine according to the axis of rotation.

6. The turbine according to claim 1, comprising a lubrication device configured to convey and discharge a lubricating fluid through the upstream casing, and to lubricate at least the first and second bearings via the lubricating fluid.

7. The turbine according to claim 1, wherein the first and second bearings are roller bearings.

8. A turbomachine comprising the turbine according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention and its advantages will be better understood upon reading the detailed description given below of different embodiments of the invention given by way of non-limiting examples. This description refers to the pages of appended figures, on which:

[0034] FIG. 1 represents a general view illustrating the operating principle of a turbomachine with counter-rotating fans according to the state of the art,

[0035] FIG. 2 represents a schematic view of a low-pressure turbine according to the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

[0036] Referring to FIG. 1, a turbomachine 10 with counter-rotating fans includes a longitudinal axis X-X. From upstream to downstream along the direction of flow of the gases 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 high-pressure body) and a downstream module C (or low-pressure turbine section).

[0037] 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.

[0038] In a manner well known per se, the high-pressure body B comprises a gas generator for producing combustion gases. This gas generator comprises a compressor 12, a combustion chamber 14 and a high-pressure turbine 16.

[0039] The air compressed by the compressor 12 is mixed with the fuel in the combustion chamber 14 before being burned therein. The thus produced combustion gases drive the movable 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.

[0040] The low-pressure turbine section C comprises a first annular rotor, or outer rotor 20. This outer rotor 20 comprises a row of outer movable blades 200 of the turbine which extend radially inwardly and which are axially spaced apart from each other.

[0041] The low-pressure turbine section C also comprises a second annular rotor or inner rotor 22. This inner rotor 22 comprises a row of inner movable blades 220 of the turbine which extend radially outwardly and which are axially spaced apart from each other. The turbine blades 200, 220 of the inner and outer rotors 20, 22 are disposed alternately relative to each other such that the inner and outer rotors 20, 22 are nested within each other.

[0042] The movable turbine blades 200 of the outer rotor 20 are rotatably supported by a first low-pressure shaft 24. Likewise, the movable turbine blades 220 of the inner rotor 22 are rotatably supported by a second low-pressure shaft. 26 disposed coaxially about the first shaft 24. The low-pressure shafts 24, 26 extend axially from upstream to downstream of the axis X of the turbomachine. The inner and outer rotors 20, 22 are surrounded by an outer casing 50.

[0043] The combustion gases coming from the high-pressure body B pass through the low-pressure turbine section C. These combustion gases therefore rotatably drive the turbine blades 200, 220 of the inner and outer rotors 20, 22 in opposite directions. Thus, the first and second low-pressure shafts 24, 26 also rotate in a counter-rotating manner.

[0044] 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 inwardly of the turbomachine.

[0045] The fan section A includes a first row of fan blades 32 mounted on an upstream fan shaft 34 which is connected to an upstream end of the first low-pressure shaft 24.

[0046] The fan section A also includes a second row of fan blades 36 which are axially spaced apart downstream of the first row of fan blades 32 and mounted on a rear fan shaft 38 connected to one upstream end of the second low-pressure shaft 26.

[0047] 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 configuration with counter-rotating fans thus gives the turbomachine high efficiency for a relatively low specific consumption.

[0048] The fan blades 32, 36 extend radially from the upstream 34 and downstream 38 fan shafts practically to the cowl 28. They are disposed in the air circulation passage supplying both the primary flowpath 40 leading to the compressor 12 of the high-pressure body B and the secondary bypass flowpath 42.

[0049] At its upstream end, the first low-pressure shaft 24 rotatably supports the second low-pressure shaft 26 via a first rolling bearing 44 and a second rolling bearing 46 disposed downstream of the first rolling bearing.

[0050] 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.

[0051] At its downstream end, the first low-pressure shaft 24 is centered and guided by a bearing 72 mounted between the first shaft 24 and a downstream casing 70 (or TRF casing, or exhaust casing) of the turbine. Furthermore, at its downstream end, the second low-pressure shaft 26 is centered and guided by a bearing 62 mounted between the second shaft 26 and an upstream casing 60 (or TVF casing) of the turbine. The bearings 62 and 72 can be roller bearings or ball bearings.

[0052] The remainder of the description describes, with reference to FIG. 2, an arrangement of the bearings of the counter-rotating turbine of the present disclosure, in particular of the low-pressure turbine C of the turbomachine 10. However, this embodiment is not limited to this low-pressure turbine, and can be adapted to other elements of the turbomachine, for example the high-pressure turbine.

[0053] According to this embodiment, the bearings 62 and 72 of the first and second low-pressure shafts 24, 26 are displaced axially along the axis of rotation X, relative to their position described with reference to FIG. 1. More specifically, the bearing 62 is always mounted between the second shaft 26 and the upstream casing 60 of the turbine. However, according to this configuration, the bearing 72 is mounted between the first shaft 24 and the upstream casing 60 of the turbine as well. In other words, the bearings 62 and 72 are both carried by the same upstream casing 60.

[0054] Particularly, the bearing 72 is disposed between the first shaft 24 and the second shaft 26. The bearing 72 is therefore an inter-shaft bearing, in which its outer end is fixed to the second shaft 26 rotating in one direction, and its inner end is fixed to the first shaft 24 rotating in a direction opposite to the first shaft 24.

[0055] In addition, the bearings 62 and 72 can be disposed in line with each other, that is to say, be substantially aligned with each other along a radial direction. In other words, they can be disposed substantially at the same axial position, along the axis X. Preferably, this position corresponds to a geometric center of the turbine C. More specifically, when the turbine C extends axially over a length L between the blade located furthest upstream along the axis X, and the blade located furthest downstream, the bearings 62 and 72 are disposed at a distance substantially equal to L/2 from the blade located furthest upstream, along the axis X. In the example of FIG. 2, the inner rotor 22 comprises four blades 220, and the outer rotor 20 comprises three blades 200 disposed between the inner blades 220. Consequently, the bearings 62 and 72 are disposed at substantially the same axial position as the central blade 200 of the inner rotor 20.

[0056] According to this configuration, the first shaft 24 is shorter than according to the configuration presented with reference to FIG. 1. Thus, the bending stresses to which the first shaft 24 is subjected are minimized.

[0057] The bearings 62 and 72 being both carried by the upstream casing 60, the downstream casing 70 is no longer necessary to carry the bearing 72, and can consequently be omitted, in order to minimize the mass of the turbine C. Likewise, unlike the turbine described with reference to FIG. 1, the outer casing 50 extends axially only over a portion less than 50%, preferably less than 30%, more preferably less than 15% of the length L of the turbine. Thus, the downstream portion of the outer rotor 20 is no longer incased by the outer casing 50. The temperatures reached by the outer rotor 20 will therefore be lower than in a configuration in which the latter is entirely surrounded by the outer casing 50, thus limiting the risk of breakdowns. Furthermore, a cooling device (not represented) can be more easily set up in order to directly cool this downstream portion. In addition, this configuration makes the outer rotor more accessible. It is thus possible to inspect the latter more easily, through an endoscope for example, without having to dismantle the engine.

[0058] Although the present invention has been described with reference to specific exemplary 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. Particularly, individual characteristics of the different illustrated/mentioned embodiments can be combined in additional embodiments. Consequently, the description and the drawings should be considered in an illustrative rather than a restrictive sense.