Improved low pressure turbine axial clearance control device

Abstract

Improved device for controlling axial clearance of low pressure turbine Low pressure turbine (60) of aircraft turbomachine, comprising an annular air flow vein, a stator with several stator stages each comprising a distributor (65) and a rotor with several rotor stages each comprising a movable wheel (64), the movable wheels (64) being carried by a rotor shaft (102) and driven in rotation by the latter about an axis of rotation (X), the low pressure turbine (60) comprising an axial clearance control device (90) capable of taking air from the annular vein at a downstream end of the low pressure turbine (60), of conveying the taken air towards a region radially internal to the rotor shaft (102), and of injecting the air at at least one injection point (P1) along the rotor shaft (102). Figure for abstract: Fig. 2.

Description

Title of the invention: Improved device for controlling the axial clearance of a low-pressure turbine Technical field

[0001] The present disclosure relates to the field of aeronautical turbomachines. More specifically, the present disclosure relates to a low-pressure turbine of an aircraft turbomachine, and in particular the management of differential clearances existing in such a turbine, and a clearance control method for such a turbine. Prior art

[0002] In a known manner, an aeronautical turbomachine turbine, in particular a low-pressure turbine, comprises a stator part and a rotor part. The stator part comprises several stator stages distributed axially along a central axis of the turbine. Each stator stage comprises a distributor comprising fixed vanes, or rectifiers, distributed around the central axis. The rotor part comprises several rotor stages also distributed axially along a central axis of the turbine, each rotor stage being axially interposed between two stator stages and comprising a moving wheel comprising vanes moving around the central axis.

[0003] In operation, the thermal inertia of the stator is less important than that of the rotor. As a result, the temperature of the stator changes more quickly than that of the rotor, which implies a greater expansion of the stator line than of the rotor line of the low pressure turbine. In order to limit the risk of contact between certain portions of the stator and the rotor, and therefore a degradation of the turbine due to these differential expansions, it is necessary to dimension the clearances between the rotor line and the stator line in order to maintain, at all times during a mission, clearances between the rotor and the stator.

[0004] For this purpose, various existing systems make it possible to take these differential expansions into account. It is notably known to use a system for active control of radial clearances during operation, by routing to ducts around the outer skin of the turbine casing, “cold” air taken upstream of the combustion chamber or in the secondary flow downstream of the fan, in order to cool the casing and close the radial clearances during engine operation to improve the performance of the low-pressure turbine.

[0005] It is also known to provide axial non-contact clearances between each rotor and stator stage, consisting of providing a sufficient margin between the stator stages and the rotor stages, making it possible to absorb the relative displacement of the stator towards the downstream side of the flow.

[0006] Nevertheless, the needs for performance gain, and therefore for limiting the fuel consumption, require limiting these clearances. Excessive clearances increase the risk of leaks. In this respect, the implementation of these axial clearances must also take into account the axial overlap between the rotor and stator parts. Indeed, in order to limit air leaks from the air flow path to the regions radially internal and external to this path, i.e. air leaks passing radially above or below the moving blades, it is necessary to provide axial overlaps between the rotor and the stator, by installing spoilers at the level of the moving blade platforms, partially covering the rectifier platforms.

[0007] Consequently, it is difficult to increase the axial non-contact clearances between the stator parts and the rotor parts, without harming the axial overlap distances between these parts, and therefore the efficiency of the turbine, the reduction in the overlap distance in fact involving an increase in air leaks. Conversely, the increase in the axial overlap distances, and therefore the reduction in the axial clearances between the stator parts and the rotor parts, increases the risk of contact between these parts due to differential expansions in certain flight phases.

[0008] There is therefore a need for a solution that at least partially overcomes the aforementioned drawbacks and improves the management of differential clearances in low-pressure turbines. Statement of the invention

[0009] The present disclosure relates to a low-pressure turbine of an aircraft turbomachine centered on an axis of rotation, comprising an annular air flow duct, a stator with several stator stages each comprising a distributor and a rotor with several rotor stages each comprising a moving wheel, the moving wheels being carried by a rotor shaft and driven in rotation by the latter around the axis of rotation, the low-pressure turbine comprising an axial clearance control device capable of taking air from the annular duct at a downstream end of the low-pressure turbine, of conveying the taken air towards a region radially internal to the rotor shaft, and of injecting the air at at least one injection point along the rotor shaft.

[0010] In the present disclosure, the terms “axial”, “radial”, “circumferential”, “internal”, “external” and their derivatives are defined relative to the central axis of the turbomachine, in other words the axis of rotation of the turbine. Furthermore, the terms “upstream” and “downstream” are defined relative to the normal direction of circulation of the air in the turbomachine, in particular in the annular air flow vein.

[0011] It is understood that the rotor shaft is the low pressure shaft carrying the rotor portion of the low pressure turbine. It is further understood that the air from the combustion chamber flows into the annular air flow vein from an upstream end from the low pressure turbine to a downstream end, i.e. at the outlet of the low pressure turbine. At this point along the flow path, the air temperature is known and controlled, and is relatively hotter, for example of the order of 500°C, than the temperature of the air present in the region radially internal to the rotor shaft, for example of the order of 300°C.

[0012] The axial play control device thus makes it possible to convey relatively hot air to the rotor shaft to inject it onto the latter, so as to heat its wall. This heating of the wall causes axial expansion of the rotor shaft. Such axial expansion causes a displacement of all the elements carried by the rotor shaft, and consequently of the entire rotor itself. In particular, an expansion of the rotor shaft causes an elongation of the latter, and therefore a downstream displacement of the moving wheels carried by the rotor shaft.

[0013] Consequently, the axial clearance control device makes it possible to expand the rotor shaft when necessary, in particular in the flight phases during which expansion of the stator takes place. It is thus possible to maintain a constant or substantially constant axial clearance between the rotor and the stator. This also makes it possible to maximize the axial overlap distance between the rotor and the stator, while limiting the risks of contact between the rotor and the stator during operation of the engine. In other words, it is thus possible to improve the sealing of the low-pressure turbine and therefore its efficiency, while improving its service life, and also limiting its axial size by reducing the cold non-contact clearances between the rotor and the stator.

[0014] In certain embodiments, the low pressure turbine comprises outlet guide vanes arranged downstream of a last rotor stage of the low pressure turbine, the axial clearance control device comprising a sampling channel capable of sampling air from the annular flow path at the outlet guide vanes.

[0015] It is understood that the outlet guide vanes are carried by an exhaust casing known by the acronym "TRF" (for "Turbine Rear Frame" in English) or "TRV" (for "Turbine Rear Vane" in English), and constitute the downstream end of the low-pressure turbine. The sampling channel samples air at this location, for example between two outlet guide vanes. This has the advantage of precisely locating the sampling site, and consequently of precisely knowing the temperature of the air sampled in the duct, and therefore of improving the precision of the control of the expansion of the rotor shaft.

[0016] In some embodiments, the axial clearance control device comprises a conveying channel adapted to convey the air taken by the bleed channel towards the region radially internal to the rotor shaft, and an injection channel comprising at least one injection nozzle adapted to inject the air at the at least one injection point along of the rotor shaft.

[0017] It is therefore understood that the axial clearance control device comprises, from upstream to downstream in a direction of air flow in the axial clearance control device, a sampling channel, a routing channel, an injection channel and an injection nozzle. The axial clearance control device can therefore be easily implemented and integrated into the low-pressure turbine. The injection of air into the region radially internal to the rotor shaft can be carried out by air impacts on the internal wall of the rotor shaft, making it possible to improve the efficiency of heat transfers and therefore control the expansion of the rotor shaft.

[0018] In certain embodiments, the at least one injection point is located radially in line with an upstream end of the low pressure turbine.

[0019] By "right", it is understood that the injection point is arranged radially opposite the upstream end of the low pressure turbine, in other words at the same axial position along the central axis as said upstream end.

[0020] Injecting the hot air taken from the annular vein at an upstream end of the low-pressure turbine makes it possible to cause an expansion of the rotor shaft at said upstream end, this expansion thus imparting the entire part of the rotor shaft downstream of the injection point, causing a downstream movement of the entire part of the rotor shaft and the moving wheels that it carries. This makes it possible to further improve the aforementioned effects, in particular the efficiency of the turbine and its service life.

[0021] In certain embodiments, the low pressure turbine comprises inlet guide vanes arranged upstream of a first rotor stage of the low pressure turbine, the at least one injection point being located radially in line with the inlet guide vanes.

[0022] It is understood that the inlet guide vanes are carried by a turbine inlet casing known by the acronym “TVF” (for “Turbine Vane Frame” in English) or “TCF” (for “Turbine Center Frame” in English), and constitute the upstream end of the low-pressure turbine. The injection channel injects air onto the rotor shaft at the same axial position as the inlet guide vanes. This has the advantage of precisely locating the injection site, and therefore of further improving the precision of the control of the expansion of the rotor shaft.

[0023] In some embodiments, the at least one injection point is a first injection point, the axial clearance control device being capable of injecting air at at least one second injection point along the rotor shaft, downstream of the first injection point.

[0024] This makes it possible to improve the speed of expansion of the rotor shaft, and thus to further improve the effectiveness of the axial play control device.

[0025] In certain embodiments, the axial clearance control device is capable of injecting air at a plurality of injection points distributed axially at regular intervals along the rotor shaft.

[0026] This makes it possible to improve the uniformity of the injection of air along the rotor shaft, and therefore to further improve the aforementioned effects, in particular the effectiveness of the axial play control device.

[0027] In some embodiments, the injection points are distributed axially over a total distance of between 80 and 120 cm along the rotor shaft. Preferably, the injection points are distributed over a total distance of 100 cm along the rotor shaft. This distance makes it possible to encompass the entire axial amplitude of the low-pressure turbine, and therefore to move axially and jointly all the moving wheels of the rotor when necessary.

[0028] In some embodiments, the axial clearance control device comprises a variable diameter shutter capable of regulating an air flow rate conveyed to the region radially internal to the rotor shaft.

[0029] It is understood that the quantity of air taken by the sampling channel is then regulated by the shutter, so as to regulate the air flowing in the routing channel, in the injection channel, and then being injected onto the wall of the rotor shaft. The shutter thus makes it possible to adapt the air flow rate according to the desired expansion of the rotor shaft, which itself must be adapted according to the expansion of the stator. The precision of the axial clearance control device and therefore its effectiveness are therefore further improved.

[0030] In some embodiments, the low pressure turbine comprises a control unit capable of regulating the shutter according to predetermined flight parameters.

[0031] The control unit may be of the FADEC type (for "Full Automatic Digital Engine Control" in English), and makes it possible to adapt the opening diameter of the shutter, and therefore the flow of air injected onto the rotor shaft, according to predetermined flight parameters involving a certain expansion of the stator of the turbine. This makes it possible to further improve the precision of the device.

[0032] In some embodiments, the predetermined flight parameters comprise at least one of altitude, flight phase, air temperature, rotor shaft rotational speed.

[0033] In certain embodiments, the rotor shaft is hollow, a central degassing tube being arranged inside the rotor shaft and being integral in rotation with the latter, the central tube comprising an external casing surrounding an internal casing delimiting an internal passage capable of receiving oil to be degassed, the external casing and the internal casing delimiting between them an annular channel, the axial clearance control device being configured to convey the air taken from the vein annular to the annular canal.

[0034] In some embodiments, the outer casing comprises a plurality of bores, the annular channel constituting the injection channel and the bores constituting the injection nozzles. The axial clearance control device thus uses equipment already present in the turbine, consequently facilitating its implementation.

[0035] The present disclosure also relates to an aircraft turbomachine comprising a low pressure turbine according to any one of the preceding embodiments.

[0036] The present disclosure also relates to a method for controlling axial clearance for a low pressure turbine according to any one of the preceding embodiments, the method comprising sampling air from the annular flow path at a downstream end of the low pressure turbine, conveying the sampled air to a region radially internal to the rotor shaft, and injecting the air at at least one injection point along the rotor shaft.

[0037] In some embodiments, the method includes regulating the flow of air delivered to the region radially inner to the rotor shaft based on predetermined flight parameters. Brief description of the drawings

[0038] The invention and its advantages will be better understood upon reading the detailed description given below of different embodiments of the invention given as non-limiting examples. This description refers to the appended pages of figures, in which:

[0039] [Fig-1] [Fig.l] schematically represents a longitudinal sectional view of a turbomachine,

[0040] [Fig.2] [Fig.2] schematically represents a longitudinal sectional view of a low pressure turbine of the invention,

[0041] [Fig.3] [Fig.3] schematically represents a detailed view of a portion of a low-pressure turbine, showing the clearances existing between a rotor and a stator,

[0042] [Fig.4] [Fig.4] schematically represents a detailed view of a downstream portion of a low pressure turbine rotor shaft, showing an example of integration of a device according to the invention. Description of the embodiments

[0043] An embodiment of the invention will be presented with reference to Figures 1 to 4.

[0044] Unless otherwise indicated, the terms “upstream” and “downstream” are hereinafter defined in relation to the direction of flow of gases through a turbomachine, indicated by the arrow F in Figures 1 and 2.

[0045] [Fig.l] illustrates a dual-flow turbomachine 100 comprising a central axis X, which is the axis of rotation of the rotating parts of the turbomachine 100, and comprising in a known manner from upstream to downstream successively at least one fan 10, an engine part successively comprising at least one low pressure compressor stage 20, high pressure compressor stage 30, a combustion chamber 40, at least one high pressure turbine stage 50 and low pressure turbine stage 60. In the present embodiment, the turbomachine module considered is the low pressure turbine 60.

[0046] In a known manner, a fraction of air is taken from the high-pressure compressor 30 and is conveyed via a cooling duct 32 in order to cool hotter zones of the turbomachine 100, in particular the high-pressure turbine 50 and the low-pressure turbine 60.

[0047] Air can also be taken from the secondary flow downstream of the fan 10 and be conveyed to channels (not shown) surrounding the external wall of the low pressure turbine 60. Such a system, known by the acronym “LPTACC” (from the English “Low Pressure Turbine Active Clearance Control”), makes it possible to cool the skin of the casing in order to control the radial clearances of the low pressure turbine 60, which makes it possible to improve the engine performance. Indeed, since the thermal inertia of the stator is less important than that of the rotor, its temperature changes more quickly than that of the rotor. The LPTACC system makes it possible to control the radial movements of the casing to maintain the most closed radial clearances possible.

[0048] [Fig.2] is an enlargement of an area of ​​the turbomachine 100, illustrating simplified way the low pressure turbine 60.

[0049] The low-pressure turbine 60 illustrated here comprises a plurality of turbine stages 61, 62, in this example three stages. A first stage 61, as well as the stages 62 located downstream thereof respectively comprise a set of fixed distributors 70 and 65. Each stage 61, 62 further comprises a movable disc 63 on which is mounted a set of movable wheel blades 64 driven in rotation by the movable disc 63. The first stage 61 of the low-pressure turbine 60 comprises a movable wheel 64, as well as at least one hollow upstream distributor 70, in which cooling air circulates.

[0050] In the example illustrated in [Fig.2], the upstream distributor 70 comprises a plurality of inlet guide vanes 74 carried by a turbine inlet casing known by the acronym “TVF” (for “Turbine Vane Frame” in English), and constitute the upstream end of the low-pressure turbine 60. This inlet casing forms a single piece with a casing 66 constituting the turbine. The upstream distributor 70 is hollow to allow cooling air to pass through, exiting via an injection device 72 associated with the upstream distributor 70, comprising a plurality of injectors.

[0051] The following stages 62, located downstream of the first stage 61, each comprise at least at least one moving wheel 64 comprising moving blades and a distributor 65 in the form of a fixed blade. The moving disc 63 is integral in rotation with a low-pressure rotor shaft 102 extending along the central axis X, while each distributor 65 is connected to the casing 66. Each turbine stage 61, 62 further comprises a sealing ring 67 located opposite the moving wheels 64, and which is integral with the casing 66.

[0052] The low pressure turbine 60 further comprises a downstream distributor 80 arranged downstream of the last stage 62 and comprising outlet guide vanes 84 carried by an exhaust casing known by the acronym “TRF” (for “Turbine Rear Frame” in English) secured to the casing 66, and constituting the downstream end of the low pressure turbine 60.

[0053] In a known manner, the turbomachine 100 comprises a cooling device making it possible to convey, via the cooling duct 32, the fraction of air taken from the high-pressure compressor 30 to the high-pressure turbine 50 and the low-pressure turbine 60. In the example described below, the fraction of air taken from the high-pressure compressor 30 flows into the cooling duct 32, then into the hollow upstream distributor 70. The direction of circulation of the fraction of air through the hollow upstream distributor 70 is illustrated by the arrows 71.

[0054] The air fraction is then injected via the injection devices 72 into a cavity radially under the vein 68, isolated in particular by a labyrinth seal 69 arranged between the upstream casing and the rotor shaft 102. The distributed air makes it possible in particular to cool the discs 63 and also allows the hot air present in the low-pressure turbine 60 to be purged, preventing the hot air coming from the combustion chamber 40 and flowing in the main air circulation vein of the low-pressure turbine 60 from penetrating into the cavity radially under the vein 68. The purging of the hot air from the low-pressure turbine 60 is here symbolized by the arrow 76.

[0055] To further limit air leaks from the vein to the regions radially internal and external to it, radial overlap zones between the stator parts and the rotor parts of the turbine are also provided. [Fig. 3] shows in detail a radially external end of a blade of the rotor wheel 64 and a blade of the distributor 65 of the stator according to the prior art, showing such an overlap. To do this, the external platform 640 of the rotor wheel blade 64 and the external platform 650 of the distributor blade 65 each comprise a spoiler, the spoilers being superimposed on each other over a distance R, corresponding to the axial overlap distance.

[0056] According to the prior art, the length of these spoilers is however limited by the risk of contact between the rotor and the stator. It is thus necessary to provide, when cold, an axial clearance J of non-contact between one end of the spoiler of the platform 650 and the blade of the wheel. 64 in order to avoid contact between these parts when the stator expands more significantly than the rotor in operation. The installation of this clearance J limits the length of the overlap distance R.

[0057] The low-pressure turbine 60 according to the invention, shown in [Fig. 2], makes it possible to overcome this drawback, thanks to an axial clearance control device 90 (hereinafter referred to more simply as “device 90”). The device 90 comprises channels for conveying air flowing in the annular air flow vein of the low-pressure turbine 60, towards a region radially internal to the rotor shaft 102. More precisely, the device 90 comprises, from upstream to downstream in a direction of air flow in the device 90, a sampling channel 91, a conveying channel 92, and an injection channel 93.

[0058] The sampling channel 91 is arranged so as to sample a fraction of air flowing in the annular vein, at the downstream end of the low-pressure turbine 60, preferably at the level of the downstream distributor 80, that is to say at the same axial position as the downstream distributor 80. This sampling location is advantageous in that the temperature at this location is known at each instant of a mission, and may for example be of the order of 500°C.

[0059] The conveying channel 92 then makes it possible to convey the air taken by the sampling channel 91 to the region radially internal to the rotor shaft 102, more precisely to the injection channel 93 arranged radially inside the rotor shaft 102. The injection channel 93 comprises at least one injection nozzle 94 making it possible to inject the air flowing in the injection channel 93 onto the wall of the rotor shaft 102.

[0060] The at least one injection nozzle 94 is arranged at the upstream end of the low-pressure turbine 60, in line with the upstream distributor 70, that is to say substantially at the same axial position as the upstream distributor 70, and makes it possible to inject the air into a first injection point PL. The injection channel 93 may comprise a plurality of injection nozzles 94, typically three injection nozzles 94 as in the present example making it possible to inject the air into a second injection point P2 downstream of the first injection point PI, and into a third injection point P3 downstream of the second injection point P2.

[0061] Preferably, the injection nozzles 94 are distributed at regular intervals axially along the injection channel 93 and the rotor shaft 102, so as to extend axially over a total distance of between 80 and 120 cm along the rotor shaft 102, typically 100 cm. The air can thus be injected uniformly at several injection points P1, P2, P3 axially distributed along the rotor shaft 102.

[0062] Furthermore, the device 90 comprises a variable diameter shutter 95, arranged in preferably between the sampling channel 91 and the delivery channel 92. Varying the diameter of the shutter 95 makes it possible to regulate the flow rate of air flowing into the delivery channel 92 and being injected by the injection nozzles 94. In other words, controlling the diameter of the shutter 95 makes it possible to control the quantity of hot air injected onto the rotor shaft 102, and thus to regulate the temperature of the internal wall of the rotor shaft 102, which therefore allows the expansion of the rotor shaft 102 to be controlled.

[0063] [Fig. 4] schematically represents an example of integration of the device 90 in the low pressure turbine 60. Typically, the rotor shaft 102 of the low pressure body is hollow and contains a central degassing tube 900, commonly called “Center Vent Tube” or “CVT”, making it possible to separate the oil from the gases present in it, by centrifugal force.

[0064] To do this, the central tube 900 comprises an upstream part fixed to the rotor shaft 102 and therefore movable in rotation with the rotor shaft 102. The downstream part (not visible) of the central tube 900 is fixed and allows the evacuation of air laden with oil. The central tube 900 can be fixed to the rotor shaft 102, for example by a first bolted connection 103 fixing a flange of an external casing 910 of the central tube 900 with a shoulder of the rotor shaft 102. The rotor shaft 102 is itself fixed, by means of a second bolted connection 105, to a transmission cone 107 allowing the transmission of the rotary torque between the rotor shaft 102 and the movable discs 63. The rotor shaft 102 is furthermore guided in rotation relative to the stator part (not shown) by a bearing 104.

[0065] In this example, the central tube 900 comprises an outer casing 910 surrounding an inner casing 920 inside which the oil / air mixture circulates. An annular channel 930 is thus created between the outer casing 910 and the inner casing 920. It will be noted that the outer casing 910 and the inner casing 920 are connected to each other by spacers 940 forming a single piece with the outer casing 910 and the outer casing 920 and allowing the annular channel 930 to maintain a constant thickness along the central axis X.

[0066] Thus, in this example, the air conveyed by the conveying channel 92 is injected into the annular channel 930, which then serves as an injection channel 93. Furthermore, a plurality of radial holes are made in the external casing 910, and serve as injection nozzles 94.

[0067] The device 90 also comprises a control unit F for controlling the diameter of the shutter 95. Typically, the control unit may be of the FADEC (Full Automatic Digital Engine Control) type and also makes it possible to control the aforementioned LPTACC system, and in particular the flow rate of air taken as a function of the flight parameters.

[0068] In the same way, the control unit F is able to regulate the flow of air taken by the device 90 as a function of the flight parameters, so as to act on the quantity of hot air injected onto the rotor shaft 102 and therefore on the expansion of the latter.

[0069] The predetermined flight parameters include, but are not limited to, the altitude, the flight phase (takeoff or landing for example), the temperature of the air in the main stream, or the rotational speed of the rotor shaft 102. Each of these parameters is characteristic of a certain temperature within the turbine, and therefore of a certain level of expansion, known beforehand, of the stator part of the turbine. It is therefore possible, by the device 90 including the control unit F, to adapt the level of axial expansion of the rotor shaft 102 so as to maintain a substantially constant axial non-contact clearance J between the stator and the rotor.

[0070] For example, when the length of the rotor shaft 102 on which action is taken is 1 m, that is to say when the injection nozzles 94 are distributed axially along the rotor shaft 102 so as to extend over a total distance of 1 m, the coefficient of linear expansion of the rotor shaft is 105 T1. Consequently, a heating of 100°C on the rotor shaft 102 implies an expansion of the downstream part of the rotor shaft of 1 mm. Thus, when the parameters detected by the control unit F are characteristic of an expansion of the order of 1 mm of the stator part, the device 90 imposes on the rotor shaft 102 an axial expansion of the same order of magnitude, this axial correction making it possible to compensate for the expansion of the stator.

[0071] According to a method for controlling axial clearance for a low-pressure turbine of an aircraft turbomachine according to the invention, the device 90 detects, via the control unit F, a predetermined flight parameter, which may be one of the parameters mentioned above and involves a certain expansion of the stator. On the basis of this detection, the control unit F controls an opening diameter of the shutter 95, in order to regulate an air flow rate flowing in the conveying channel 92 towards the injection channel 93 and the injection nozzles 94.

[0072] In this regard, the method comprises sampling air from the annular flow path via the sampling channel, at the downstream end of the low-pressure turbine 60, conveying, via the conveying channel 92, the sampled air to a region radially internal to the rotor shaft, and injecting the air into at least one injection point PI along the rotor shaft 102, via the injection channel 93 and the injection nozzles 94.

[0073] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may 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 various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0074] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

Claims

1. Low pressure turbine (60) of an aircraft turbomachine centered on an axis of rotation (X), comprising an annular air flow duct, a stator with several stator stages each comprising a distributor (65) and a rotor with several rotor stages each comprising a movable wheel (64), the movable wheels (64) being carried by a rotor shaft (102) and driven in rotation by the latter around the axis of rotation (X), the low pressure turbine (60) comprising an axial clearance control device (90) capable of taking air from the annular duct at a downstream end of the low pressure turbine (60), of conveying the taken air towards a region radially internal to the rotor shaft (102), and of injecting the air at at least one injection point (PI) along the rotor shaft (102).

2. Low pressure turbine (60) according to claim 1, comprising outlet guide vanes (84) arranged downstream of a last rotor stage of the low pressure turbine (60), the axial clearance control device (90) comprising a sampling channel (91) capable of sampling air from the annular flow path at the level of the outlet guide vanes (84).

3. Low pressure turbine (60) according to claim 2, wherein the axial clearance control device (90) comprises a conveying channel (92) capable of conveying the air taken by the bleed channel (91) towards the region radially internal to the rotor shaft (102), and an injection channel (93) comprising at least one injection nozzle (94) capable of injecting the air at the at least one injection point (PI) along the rotor shaft (102).

4. Low pressure turbine (60) according to any one of claims 1 to 3, in which the at least one injection point (PI) is located radially in line with an upstream end of the low pressure turbine (60).

5. Low pressure turbine (60) according to any one of claims 1 to 4, comprising inlet guide vanes (74) arranged upstream of a first rotor stage of the low pressure turbine (60), the at least one injection point (PI) being located radially in line with the inlet guide vanes (74).

6. Low pressure turbine (60) according to any one of claims 1 to 5, in which the at least one injection point (PI) is a first injection point, the axial clearance control device (90) being capable of injecting air into at least one second injection point (P2) along the rotor shaft (102), downstream of the first injection point (PI).

7. Low pressure turbine (60) according to any one of claims 1 to 6, in which the axial clearance control device (90) is capable of injecting the air at a plurality of injection points (PI, P2, P3) distributed axially at regular intervals along the rotor shaft (102).

8. Low pressure turbine (60) according to claim 7, wherein the injection points (PI, P2, P3) are distributed axially over a total distance of between 80 and 120 cm along the rotor shaft (102).

9. A low pressure turbine (60) according to any one of claims 1 to 8, wherein the axial clearance control device (90) comprises a variable diameter shutter (95) capable of regulating an air flow rate conveyed to the region radially internal to the rotor shaft (102).

10. Low pressure turbine (60) according to claim 9, comprising a control unit (F) capable of regulating the shutter (95) according to predetermined flight parameters.

11. The low pressure turbine (60) of claim 10, wherein the predetermined flight parameters comprise at least one of altitude, flight phase, air temperature, rotational speed of the rotor shaft (102).

12. Low pressure turbine (60) according to any one of claims 1 to 11, in which the rotor shaft (102) is hollow, a central degassing tube (900) being arranged inside the rotor shaft (102) and being rotationally integral therewith, the central tube (900) comprising an outer casing (910) surrounding an inner casing (920) delimiting an internal passage capable of receiving oil to be degassed, the outer casing (910) and the inner casing (920) delimiting between them an annular channel (930), the axial clearance control device (90) being configured to convey the air taken from the annular vein towards the annular channel (930).

13. A low pressure turbine (60) according to claims 3 and 12, wherein the outer casing (910) comprises a plurality of bores, the annular channel (930) constituting the injection channel (93) and the bores constituting the injection nozzles (94).

14. Aircraft turbomachine (100) comprising a low pressure turbine (60) according to any one of the preceding claims.

15. Method for controlling axial clearance for a low pressure turbine (60) according to any one of claims 1 to 13, the method comprising drawing air from the annular duct at a downstream end of the low pressure turbine (60), conveying the drawn air to a region radially internal to the rotor shaft (102), and injecting the air at at least one injection point (PI) along the rotor shaft (102).

16. A method according to claim 15, comprising regulating the flow of air delivered to the region radially internal to the rotor shaft (102) in accordance with predetermined flight parameters.

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