Gas turbine for twin-rotor aircraft

Abstract

The invention relates to a turbine comprising a first rotor (22a) and a second rotor (22b) which can rotate in opposite directions and are staggered. The turbine further comprises a ring (66) to which a wear-resistant material (68) is fixed, the ring (66) being unsegmented and extending over a sector between 350 and 360° between a first impeller (22aa) of the first rotor and the second rotor (22b), and axially between the upstream and downstream ends of the ring (66), the ring being held together with the second rotor (22b).

Description

Technical Field

[0001] The field of the invention is that of gas turbines for aircraft and, in particular, that of turbofans or turbofan engines for aviation. Background Art

[0002] As a preface, let me first point out:

[0003] - any turbomachine and / or turbine referred to herein generally has a common X-axis substantially parallel to the direction of gas flow from upstream to downstream, this axis being the axis of rotation of any rotor of said turbomachine or turbine,

[0004] - "outer" and "inner" refer to positions radially relative to the X-axis; the outer position is a position further from the X-axis and the inner position is a position closer to the X-axis, and

[0005] - "Circumferential" (or "tangential") means: around the X-axis, extending around the X-axis.

[0006] A gas turbine engine for an aircraft (e.g. a turbofan, which is a twin-casing, twin-flow engine) comprises a fan, which is usually driven directly by a low-pressure turbine (hereinafter referred to as the LP turbine) and is axially arranged upstream of the low-pressure turbine, which is located downstream of a high-pressure turbine (hereinafter referred to as the HP turbine). The combustion chamber is axially inserted between the downstream HP turbine and the upstream LP (low-pressure) compressor, and the turbine downstream of the upstream LP compressor also includes an HP (high-pressure) compressor. This configuration with a fan directly driven by the LP turbine has the following disadvantages: the fan rotates at the same speed as the LP turbine. However, in order to achieve a good specific fuel consumption and a low noise level, the fan should rotate as slowly as possible, while adjusting the blade profile to maintain a high airflow and speed, thereby maintaining the required thrust level.

[0007] Besides the technical solution of placing the gearbox on the shaft connecting the fan and the LP turbine, as an alternative turbofan engine, it has been proposed that, since the turbine extends around an axis (X), it comprises:

[0008] - a first rotor, comprising a first running wheel (or impeller), and

[0009] - a second rotor comprising a second running wheel (or impeller), the first and second rotors being rotatably mounted about said axis (X), said first rotor and said second rotor being configured to rotate in opposite directions, at least some of the second impellers being axially inserted between at least some of the first impellers.

[0010] Thus, for example, in FR2942273, the LP turbine comprises a first rotor, a portion of which rotates axially around a second impeller. The fan is driven by the second rotor via a second turbine shaft and by the first rotor via a first turbine shaft, the first turbine shaft rotating in the opposite direction to the second shaft, the counter-rotating turbine having the advantage of having a smaller footprint to perform the same function as a conventional turbine.

[0011] Invention Disclosure

[0012] In the problem that the present invention seeks to provide a technical solution, the following points can be noted:

[0013] -The critical part that must be retained will be considered the second rotor,

[0014] - This second rotor must, if possible, be protected from damage that could result from the release of blades or parts of these blades with which said rotor is equipped, in particular if such release is not detected quickly

[0015] - The fixing of the blades of the first rotor must be ensured. Summary of the invention

[0016] A technical solution proposed to some or all of the above problems is that the above known gas turbine further comprises a ring to which the wear-resistant material is fixed,

[0017] - a ring extending around the rotation axis between the first impeller (at least one of the first impellers) and the second rotor, and

[0018] Axially between the upstream and downstream ends of the ring, the ring is held together with the second rotor.

[0019] Thus, in other words, the turbine comprises said ring, to which the wear-resistant material is fixed, said ring extending around one of the first impellers, with which the wear-resistant material cooperates.

[0020] In practice, the wear-resistant material is inserted between the ring and said one of the first impellers and surrounds said impeller.

[0021] Thus, the wear-resistant material is fixed relative to the ring; however, one of the first impellers is movable relative to the wear-resistant material (rotatable about the X axis),

[0022] By being in contact with the wear-resistant material, the first moving wheel cooperates with or engages with said wear-resistant material during rotation of the turbine.

[0023] This helps to retain the blades of the first impeller without damaging the (radially external) part of the second rotor. In practice, on a conventional turbine (i.e. a turbine having only an internal rotor, without an external rotor, but instead having an external stator), any such ring is fixed to the external stator, which is generally a fixed turbine casing, and then performs the retaining function: in this case, the ring is merely complementary to the retaining. Conventional turbine rings are therefore in sector form, which facilitates their manufacture and mechanical strength. In the counter-rotating turbine of the invention, the ring is fixed to the second rotor. Therefore, the retention of the blades of the first rotor (whose blades may generally be radially internal with respect to a part of the second rotor surrounding them) must be ensured by one or more strong, durable rings to protect the second rotor (its aforementioned surrounding part).

[0024] It may be advantageous to choose the ring to extend over an angular sector between 350 and 360°.

[0025] Therefore, a ring made in an axisymmetric manner and therefore over 360° may be preferred, which ring cannot open under the impact of the released blades and is best suited to retention. However, a ring split between 350° and less than 360° can also be chosen to facilitate assembly and maintenance of the ring.

[0026] Furthermore, by maintaining the ring in the above-mentioned axial position on the second rotor, the ring will have a certain axial expansion capability when the turbine is running.

[0027] To facilitate this, it is also proposed that said retention of the ring to the second rotor is located axially closer to the centre of the ring than to said upstream and downstream ends.

[0028] The ring will be held axially with the second rotor by a rotating coupling which may comprise a dog clutch coupling (see below).

[0029] In the case where the upstream and downstream ends can be fixed axially (and preferably radially) only by means of said rotational coupling, the ring will have an advantageous freedom of deformation when the turbine is in operation, without having actual constraints.

[0030] And keeping the ring axially close to its center will promote more accurate ring balancing and less vibration in the turbine.

[0031] According to another feature, it is also proposed that for said retention of a ring to the second rotor, said ring has a central cylindrical bearing extending axially at the centre of said ring.

[0032] This position allows the ring to be efficiently and easily balanced during manufacturing and assembly.

[0033] Advantageously, the cylindrical bearing will be retracted into the second rotor.

[0034] The advantage is a very precise centering of the ring on the second rotor.

[0035] It also proposes:

[0036] - the ring has two first axial cylindrical surfaces, one upstream and one downstream, respectively, one being located further upstream than the other at the outer periphery of the ring,

[0037] the second rotor has two second axial cylindrical surfaces, upstream and downstream respectively, located radially opposite the first upstream and downstream cylindrical surfaces, respectively, at the inner periphery of a portion of the second rotor, and

[0038] - During normal operation of the turbine, a radial gap is established between the first cylindrical surface of the ring and the second cylindrical surface of said portion of the second rotor, respectively.

[0039] This in turn ensures good control of the operating clearance, and in particular the differential expansion, between the wear-resistant material and the blades of the first rotor.

[0040] Additionally and specifically for counter-rotating turbines, precise centering of the ring on the second rotor also allows for more precise balancing and thus less vibrations in the turbine.

[0041] According to yet another characteristic, it is proposed that for the axial stop of the ring and for said retention of the ring to the second rotor, a rotational coupling is established between the ring and the second rotor.

[0042] Preferably, this rotational coupling will be established in the axially central portion of the ring.

[0043] Thus, an effective axial stop and a safe and rebalanced attachment (fastener) in terms of mechanical stresses will be provided between the ring and the second rotor.

[0044] In order to achieve this rotational connection for the same purpose, it is also proposed that the rotational coupling comprises an axial stop between at least one radially outwardly projecting protrusion on the ring and at least one cooperating recess on the second rotor.

[0045] Advantageously, the rotary coupling will comprise a dog clutch coupling.

[0046] This will allow the translation stop to be close to the above-mentioned centering of the ring and will help to reduce the axial stresses in the ring. This is a technical solution that complements the non-sectorized ring.

[0047] In addition, a circumferential (also called tangential) bearing will be established between the ring and the blades directly downstream of the ring; usually adjacent to the above-mentioned first and second downstream axial cylindrical surfaces (if present). For this purpose, a rotating coupling member via a pin and mortise can connect the ring to an axially adjacent second impeller.

[0048] This should:

[0049] - allows the ring to stop rotating (about the X axis) in an efficient manner that is extremely easy to produce and install, and

[0050] - Prevent the ring from being gripped (claw-shaped).

[0051] Preferably, the wear resistant material will be presented circumferentially as a series of annular sectors.

[0052] This will facilitate the manufacture, installation of wear-resistant material on the rings and their replacement.

[0053] According to yet another feature, a gas turbine engine for an aircraft is also proposed, the turbine engine having an upstream inlet for the entry of gases and a downstream outlet for the exit of gases, the turbine engine comprising:

[0054] - a turbine as described above having all or part of its features, said turbine being a LP turbine, and

[0055] - A HP turbine located upstream of the LP turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 A schematic axial cross-sectional view showing a possible embodiment of a counter-rotating turbine according to the invention,

[0057] Figure 2 showing an enlarged view of the first and second rotors; Figure 1 Region II,

[0058] Figure 3 A schematic diagram showing an assembly comprising said ring (hereinafter 66) to which a wear-resistant material (hereinafter 68) is fixed,

[0059] Figure 4 represents an alternative embodiment of the assembly,

[0060] Figure 5 Indicated in Figure 2 A diagram of a vertical segment in region V of ,

[0061] Figure 6 represents a perspective view of a tear with this region V,

[0062] Figure 7 represents an alternative embodiment of said region V,

[0063] Figure 8 Another embodiment variant of this region V is shown,

[0064] Fig. 9 Another point on the circumference shows Figure 6 Schema,

[0065] Fig.10 Show Fig. 9 The XX section, and

[0066] Fig.11 Shown in Fig.10 The area around the hollow body 823. DETAILED DESCRIPTION

[0067] The following refers to implementations which are presented as examples only.

[0068] therefore, Figure 1 The drawing in illustrative embodiment illustrates a counter-rotating geared turbine 10 for an aircraft.

[0069] This turbomachine 10 includes, from upstream to downstream in the airflow direction from upstream (US) axial to downstream (DS), a fan 12, a low-pressure compressor 14, a high-pressure compressor 16, an annular combustion chamber 18, a high-pressure turbine 20 and a low-pressure (also called LP) counter-rotating turbine 22.

[0070] Reference numeral 23 denotes an intake casing located between the fan 12 and the compressor 14. Reference numeral 24 denotes an intermediate casing between the compressors 14 and 16, and reference numeral 26 denotes a turbine casing (TVF type) between the turbines 20 and 22. Reference numeral 28 denotes an exhaust casing (TRF type).

[0071] The high-pressure turbine rotor 20 rotates the high-pressure compressor rotor 16 via a high-pressure shaft 30 which is centrally located and guided in rotation by bearings such as an upstream bearing 32 and a downstream bearing 34 .

[0072] The counter-rotating turbine 22 includes a first rotor 22a having a wheel 22aa (also referred to as a first impeller) configured to rotate in a first rotational direction and connected to a first turbine shaft 36, and a second rotor 22b having a wheel 22ba (also referred to as a second impeller) configured to rotate in an opposite rotational direction and connected to a second turbine shaft 38. The wheel 22ba is axially inserted between the wheels 22aa. The first rotor 22a and the second rotor 22b are surrounded by a housing 29, the downstream end of which includes a flange for attachment (fixing) to the exhaust housing 28.

[0073] The first shaft 36 in the example extends axially within the shaft 30 and rotates the low-pressure compressor rotor 14. The first shaft 36 is further coupled to an input shaft 36a which meshes with a sun or planetary gear, for example with an epicyclic gear train, of a mechanical gearbox 42. The input shaft 36a is thus rotatably fixed to the shaft 36.

[0074] The second shaft 38 in the example extends within the shaft 36 and rotates the fan 12. The second shaft 38 is coupled to a fan housing 39 and an output shaft 38a which meshes with a ring gear 5 of a gearbox 42.

[0075] The gearbox 42 further comprises satellites meshed with the sun gear and the ring gear respectively and carried by satellite holders 42a. The satellite holders may be fixed or movable. In a planetary gearbox, the satellite holders are movable, in a planetary gearbox, the satellite holders are fixed. The satellite holders 42a may or may not be fixed to the input housing 23.

[0076] The first shaft 36 is centrally and guided upstream by a bearing 48 mounted between the first shaft 36 and the intermediate casing 24 , and downstream by a bearing 50 mounted between the first shaft 36 and the turbine casing 26 .

[0077] The second shaft 38 is centrally located and guided upstream by a bearing 52 mounted between the second shaft 38 and the first shaft 36 , and downstream by a bearing 54 shown between the second shaft 38 and the exhaust casing 28 .

[0078] The fan shaft 39 and the output shaft 38a are guided by upstream bearings 56 and downstream bearings 58. These bearings 56, 58 are located upstream of the gearbox 42, firstly between the fan shaft 39 and the output shaft 38a, and secondly between the fan shaft 39 and the intake housing 23. Downstream of the gearbox 42, a bearing 60 guides the rotation of the input shaft 36a and is mounted between this shaft and the input housing 23.

[0079] Both impellers 22aa and 22ba include blades on the outer periphery, referenced 221 and 222 respectively.

[0080] from Figure 2 As best seen in the diagram of FIG. 2 , impeller 22aa is coupled for common rotation by portion 62a of first rotor 22a, and impeller 22ba is coupled for likewise common rotation by portion 62b of second rotor 22b.

[0081] The portion 62a of the first rotor 22a and the portion 62b of the second rotor 22b may each be defined by an annular portion that is integrated through 360° around the X-axis.

[0082] Portion 62b surrounds wheel 22ba and also surrounds wheel 22aa as well as portion 62a.

[0083] exist Figure 6 The area of ​​portion 62b is best seen in FIG.

[0084] According to the present invention, at least one assembly 64 (specifically, Figure 2 22aa) is inserted radially between the portion 62b and the free outer ends 220a of the blades of the wheel 22aa, the assembly comprising at least one ring 66 extending circumferentially over a sector between 350 and 360° and to which abrasion-resistant material 68 is fixed (see Figures 4 to 6 ).

[0085] At the outer periphery, the impeller blades 22aa have knife edge seals 70, at least one per blade.

[0086] To seal in the airflow 72 extending from the blades 221 and 222 , the knife edge seal ( 70 ) contacts the abradable material 68 during rotation of the turbine 22 .

[0087] Thus, the ring 66 extending around the axis of rotation X between the first impeller 22aa and the second rotor 22b is not segmented, as can be seen in Figure 3 Or as shown in 4.

[0088] Furthermore, in order to facilitate the fact that the ring 66 has a certain axial expansion capability, when the turbine is in operation, the turbine is provided axially between the upstream end 66a and the downstream end 66b of the ring, which is held on the second rotor 22b (its portion 62b), being fixed thereto; see in particular Figures 5 to 6 .

[0089] In order to further promote this and thus further minimize the stresses caused by the different axial expansions between the ring 66 and the second rotor 22 b, by ensuring that the upstream and downstream ends of the ring are free to expand axially, it is even proposed that the retention (the singular does not exclude several retentions) of the ring 66 to the second rotor 22 b is axially closer to the center of the ring than to said upstream end 66 a and downstream end 66 b (see Figures 5 to 8 The region 660) is positioned in which the ring will not be axially retained with the second rotor 22b.

[0090] Holding (engaging) in this region 660 axially close to its center, the ring will be well balanced and fewer vibrations will be generated in the turbine.

[0091] With regard to retention, the following items are proposed:

[0092] The ring 66 has a central cylindrical bearing surface 661 which is therefore located substantially in the center of the ring parallel to the axis of rotation X (see in particular Figure 5 , 7 and 8).

[0093] - In the axial centre portion 660 of the ring (see the same figure), a rotation coupling 74 is established between the ring 66 and the second rotor 22b (the portion 62b thereof).

[0094] A central cylindrical bearing surface 661 will thus be present at the outer periphery of the ring, which, both at rest and when the turbine is in operation, corresponds in complementary manner to a portion 62b arranged in the second rotor 22b (see in particular Figure 5 , 7 The cylindrical supports 76 on the rotor 8) are opposite and in radial contact, which contributes to an effective and easy implementation of the balancing of the rings during manufacture and assembly. Advantageously, the cylindrical bearing 661 will be shrunk into the second rotor.

[0095] This allows better control of the clearance between the wear-resistant material 68 and the sealing elements 70 of the blades of the first rotor 22a, each of which is arranged on a blade platform 222 / 222a of the first rotor (see Figure 5 ) on the outer periphery, and they themselves must cooperate on the outer periphery with the wear-resistant material 68 subsequently provided (fixed) on the radially facing portion 62b of the second rotor 22b.

[0096] By rotating the coupling 74, the attachment (fixing) will be secure and balanced again in terms of mechanical stresses between the ring and the second rotor 22b.

[0097] The rotation coupling 74 may include an axial stop 740 between at least one radially outwardly projecting protrusion 663 on the ring 66 and at least one radial groove 620 on the second rotor portion 62b; see Figures 6 to 8 .

[0098] Each protrusion 663 may be formed by teeth distributed circumferentially in several ring sectors.

[0099] Although located in the axial central portion 660, the rotary coupling 74 and therefore the cooperating projections and recesses 663, 620 can be axially positioned differently relative to the centering formed by the cylindrical bearing surface 661 and its cylindrical support 76: just downstream of this centering, as in Figure 5 In the technical solution; upstream of the centering, such as in Figure 7 in the technical solution of; or in the middle of the latter, such as in Figure 8 Therefore:

[0100] -exist Figure 7 In the technical solution, it is described that the upstream wall 620a of the groove 620 is supported against the protrusion 663 on the upstream side, while the centering walls 661, 76 are located further downstream,

[0101] -exist Figure 8 In the technical solution, it is described that the protrusion 663 on the downstream side is supported against the downstream wall 620b of the groove 620, and the centering walls 661, 76 are adjacently axially distributed between the upstream continuity and the downstream continuity of this rotating coupling 74.

[0102] If referred to as "center", the cylindrical bearing 76 will be located substantially at the center 660 of the ring: the axial center of the ring is defined as the length L1 between its upstream end 66a and downstream end 66b (see Figure 8 ), including the axial teeth 821 (see below). The axial center portion 660 extends axially on either side of this center for a length that may be between 10% and 30% of the length L1. Up to about 25% on one side and up to about 5% on the other side are conceivable, such as in a case where only at least a portion of the upstream centering wall 661, 76 is located upstream of the middle of the length L1. Figure 8 In the middle, the rotating coupling 74 and the downstream parts of the centering walls 661 and 76 are located downstream of this middle.

[0103] Advantageously, the rotary coupling 74 will comprise a dog clutch. For this purpose, the projections and recesses 663, 620 can engage with each other to form a circumferential dog clutch.

[0104] WO2016189222 or FR3036433 provide examples of dog clutches. If there is already a shrink fit of the centering (see above), the shrink fit is already suitable for allowing relative manual rotation during the dog clutch.

[0105] In any case, this rotational and translational stop close to the above-mentioned centering 76, 661 of the ring will help to reduce the axial stresses in the latter.

[0106] This is a technical solution to supplement the non-sectorized ring 66 .

[0107] In this regard, Figure 3 The assembly 64 is illustrated as comprising a ring 66 extending 360° around the X-axis. Figure 4 An assembly 64 is illustrated, comprising a ring 66 spanning 350° of annularity, thus presenting itself as a split ring on its circumference at 641. Although this allows engagement with circumferential elastic deformation, this split solution is not as safe as a 360° annular, axisymmetric solution which cannot open under the impact of releasing the blades.

[0108] In each case, the wear-resistant material 68 will preferably be implemented in sectorized or non-sectorized blocks (not shown), each of which can be conventionally and removably secured to the ring 66 on its inner circumference.

[0109] More specifically, Figure 5 and 7 As shown in , it is also proposed that in the event of an abnormal situation (for example, blade impact or local overheating), upstream brackets 78a and downstream brackets 78b are advantageously arranged between the ring 66 and the portion 62b of the second rotor. These upstream brackets 78a and downstream brackets 78b are not present during normal operation of the turbine, nor are they present when stationary, wherein for the ring 66 and the portion 62b, there is a radial gap between the corresponding surfaces that will be subsequently marked as 665a, 80a at the upstream end and 665b, 80b at the downstream end; see Figure 7 .

[0110] Thus, the ring 66 will then have two first axial cylindrical surfaces, respectively upstream 665a and downstream 665b, one situated more upstream than the other at the outer periphery of the ring, and the portion 62b of the second rotor will have two second axial cylindrical surfaces, respectively upstream 80a and downstream 80b, situated radially opposite the first upstream and downstream cylindrical surfaces, respectively, at the inner periphery of said portion 62b.

[0111] This should help control the wear resistant material 68 and the blades 222 (or Figure 5 Or 222a, 222b in 10) between the operating gap and in particular the axial expansion of the sealing elements 70.

[0112] However, it should be noted that the centering solution between the central cylindrical bearing surface 661 and the cylindrical support 76 and the rotating coupling 74 is independent of these functions and can be provided separately on the ring 66, such as Figure 8 as shown in .

[0113] In this solution, only the centering support between the central cylindrical bearing surface 661 and the cylindrical support 76 and the rotating coupling 74 remains (compared to the above). In the event of an abnormal situation as mentioned above, the axial cylindrical surfaces of the upstream support 78a and the downstream support 78b are removed.

[0114] In any case, in both cases, at least one circumferential bearing surface (also called tangential, about the X-axis) will also preferably be established between the ring 66 and a blade (for example, blade 222b) which is located at Figure 5 axially downstream of the ring 66 and therefore also axially downstream of the vane 222a, the sealing element 70 of which cooperates with the wear-resistant material 68; see Figure 5 or 10.

[0115] Thus, in 82, the ring 66 is connected to the axially adjacent second impeller (22ba) via a rotational coupling member of a socket and groove.

[0116] Circumferential bearing surface 82 (or each of them, since there may be several circumferentially and / or when there are several rows of blades on the turbine, as in Figure 2 In the example of the embodiment of the present invention, there are three of them) can be implemented by an axial tooth 821 protruding downstream on the downstream edge, which is at the downstream end 66b of the ring 66 and engages quite closely with the axial tooth formed on the blade concerned (for example, Fig.10 222 / 222b) may have a complementary recess 823 on the upstream face of the annular connecting portion 84 to attach (fix) to the portion 62b of the second rotor 22b at the outer circumference; see also Fig.11 .

[0117] This will effectively and relatively easily implement and assemble, prevent loosening and allow each ring 66 to be rotatably locked relative to (the connecting ring portion 84 of) the adjacent downstream row of impellers 222a of the first impeller 22aa.

Claims

1. A gas turbine for an aircraft, the turbine extending about an axis (X) and comprising a first rotor (22a) comprising a first impeller (22aa); and a second rotor (22b) comprising a second impeller (22ba), the first and second rotors being rotatably mounted about the axis (X), the first rotor (22a) and the second rotor (22b) being configured to rotate in opposite directions, wherein at least some of the second impellers (22ba) are axially inserted between at least some of the first impellers (22aa), characterised in that: - the turbine further comprises a ring (66) to which a wear-resistant material (68) is fixed, the ring (66) extending around one of the first impellers (22aa), the wear-resistant material (68) cooperating with the first impeller, and - axially between the upstream end (66a) and the downstream end (66b) of the ring (66), the ring being held together with the second rotor (22b), In order to achieve axial stopping of the ring and fixation with the second rotor, a rotary coupling is established between the ring and the second rotor, and wherein the rotary coupling comprises an axial abutment between a plurality of radially outwardly projecting protrusions on the ring and a plurality of mating grooves on the second rotor, and Wherein, the rotary coupling comprises a dog clutch, which is formed by the plurality of radially outwardly protruding protrusions and the plurality of mating grooves, and the plurality of mating grooves and the plurality of radially outwardly protruding protrusions are engaged with each other.

2. The turbine according to claim 1, characterized in that The ring (66) extends over an angular sector between 350 and 360°.

3. The turbine according to claim 1, characterized in that The retention of the ring (66) to the second rotor (22b) is located axially closer to the center (660) of the ring than to the upstream and downstream ends (22b).

4. The turbine according to claim 1, characterized in that For the retention with the second rotor (22b), the ring (66) has a central cylindrical bearing (76) extending axially at the center (660) of the ring (66).

5. The turbine according to claim 4, characterized in that The cylindrical bearing (76) of the ring is retracted into the second rotor (22b).

6. The turbine according to claim 1, characterized in that: - the ring (66) has two first axial cylindrical surfaces, upstream and downstream respectively (665a, 665b), one being located more upstream than the other at the outer periphery of the ring (66), - the second rotor (22b) has two second axial cylindrical surfaces, upstream and downstream (80a, 80b), respectively, located radially opposite to the upstream and downstream cylindrical surfaces (665a, 665b), respectively, at the inner periphery of the portion (62b) of the second rotor (22b), and - During normal operation of the turbine, a radial gap is established between a first cylindrical surface of the ring (66) and a second cylindrical surface of the portion (62b) of the second rotor (22b), respectively.

7. The turbine according to claim 1, characterized in that The rotary coupling (74) is located at the axial center portion (660) of the ring (66).

8. The turbine according to claim 1, characterized in that A mortise and tenon type rotary coupling member connects the ring (66) to a second impeller (22ba) axially adjacent to the ring.

9. A turbine engine for an aircraft, the turbine engine having an upstream inlet through which gases enter and a downstream outlet through which gases leave, the turbine engine comprising: - a turbine (22) according to any one of the preceding claims, said turbine being a low-pressure turbine, and - A high-pressure turbine (20) situated upstream of said low-pressure turbine (22).

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