TURBOMACHINE COMPRISING AN OVERSPEED LIMITING DEVICE

Abstract

The invention relates to a turbomachine comprising at least one compressor and at least one turbine comprising a rotor connected by a shaft to a rotor of the compressor, the rotor of the turbine comprising at least one blade surrounded by a stator casing of the turbine, the turbine comprising at least: an annular sealing device carried by the casing and comprising at least one first element mobile in tilting following a downstream movement of the turbine, from a sealing position in which it is in radial support on an upstream edge of the blade, and a tilted position in which it is axially spaced from said upstream edge; and an overspeed limiting device of said shaft comprising at least one projectile housed in said space and configured to be released into the turbine when the first element passes from its release position to its tilted position. Figure for abstract: Fig. 5

Description

Title of the invention: TURBOMACHINE COMPRISING AN OVERSPEED LIMITING DEVICE Technical field of the invention

[0001] The invention relates to a turbomachine, for example a turbojet, comprising a device for limiting overspeed of a turbine rotor of this aircraft turbomachine. Technological background

[0002] The phenomenon of overspeed of a turbine rotor is in principle a rare phenomenon.

[0003] For example, in the case of a turbojet, which conventionally comprises a low pressure rotor coupled to a turbojet fan, and in which the coupling is achieved by means of two shafts and a reducer, when present, mounted in series, such a phenomenon can occur when the shaft which connects the low pressure rotor to the reducer breaks, or when an internal organ of the reducer breaks, or when the shaft which connects the reducer to the fan breaks.

[0004] When one of these shafts or the internal component of the reducer breaks, the turbine rotor is consequently mechanically uncoupled from the fan, which then no longer exerts any resistive torque on this shaft and which consequently no longer limits its rotation speed.

[0005] However, the moving blades of the turbine continue to be driven in rotation by the gases leaving the combustion chamber of the turbomachine. The turbine then goes into overspeed, which subjects the turbine rotor to excessive centrifugal forces which are likely to cause it to burst and consequently the release of debris having high kinetic energy, with the consequence of risks of perforation of the external casing of the turbine and also of the fuselage of the aircraft which is equipped with this turbomachine. The overspeed limitation is therefore an imperative constraint to be respected in turbomachines.

[0006] The axial position of the turbine rotor shaft is determined in particular by a thrust bearing and by its coupling to the reducer when the latter is present.

[0007] Known overspeed limitation devices generally exploit the fact that the rupture of the turbine shaft allows a downstream movement of the turbine rotor under the action of the pressure of the gases on the rotor blades. Thus, mechanical braking devices for the turbine rotor have already been proposed, comprising means carried by the turbine rotor and intended to bear on corresponding means of a corresponding stator or distributor so as to brake the turbine rotor, following its downstream movement after the rupture of the turbine shaft.

[0008] It has also been proposed, within the same stage of the turbine, to mount the guide vanes of the stator in a removable or tilting manner so that the rotor, due to its movement downstream after the rupture of the turbine shaft, comes to bear on these vanes and makes them tilt onto the path of the moving vanes to destroy them and thus slow down the rotation of the turbine.

[0009] Finally, a technical solution has been proposed consisting, within the same stage of the turbine, of providing the blades of a stator blade with an area in the form of an axial deviation of the shape of said blades called "crown", allowing a blade of the turbine rotor, when it moves back during the breakage of the turbine shaft, to see the moving blades of its blade come into contact with the crown area of ​​the stator blades in order to destroy the blades of the moving blades and thus slow down the rotation of the turbine. This destruction operation is, for this reason, known as "feathering" the turbine.

[0010] In the particular case of a breakage of the shaft connecting the reducer to the fan, the overspeed of the turbine shaft can also risk causing the destruction of the reducer, because it is then driven at rotation speeds for which it is not designed.

[0011] Furthermore, this "plumage" solution can lead to the modification of the aerodynamic profile of the components of the turbomachine to the detriment of its performance in normal operation. Indeed, the "domed" profile is not optimized from an aerodynamic point of view, which can impact the efficiency of the stator blades. In addition, the "domed" profile imposes a constraint relating to the clearances between the turbine blades. Indeed, the clearances between the blades of a rotor blade and those of an adjacent stator blade must be reconfigured to ensure effective destruction of the turbine and avoid other phenomena such as rim cutting, which can lead to the destruction of the turbomachine in its entirety.

[0012] It may thus be desirable to provide a turbomachine which makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention

[0013] The invention aims in particular to provide a simple, economical and effective solution to these problems, making it possible to avoid the drawbacks of the known technique. The invention aims in particular to allow the destruction of several stages of turbine blades, and preferably, of all the stages of the turbine.

[0014] For this purpose, the invention proposes a turbomachine comprising at least one overspeed limitation device which projects at least one free projectile onto the blades of at least one blade of the turbine.

[0015] By "free" it is understood that the projectile is projected free from any connection, in particular mechanical, with any part of the turbomachine and that it is therefore free to move in the vein of the turbomachine.

[0016] In the present invention, the turbomachine, in particular an aircraft turbomachine, comprises at least one compressor, an annular combustion chamber and at least one turbine, the turbine comprising a rotor connected by a shaft to a rotor of the compressor, the rotor of the turbine comprising at least one blade surrounded by a stator casing of the turbine, and the turbine comprising an annular sealing device carried by the casing and which extends around a longitudinal axis of the turbomachine, said sealing device cooperating with an external periphery of the blade, the turbomachine further comprising a device for limiting overspeed of said shaft, the rotor of the turbine being intended to move downstream along the longitudinal axis in the event of rupture of an element of the turbomachine, characterized in that: - the annular sealing device comprises at least a first element which is capable of bearing radially inwards on an upstream annular rim of the external periphery of the blading, this annular element comprising or defining an annular space which extends radially between this element and the casing, this first element being carried by the casing and movable in tilting, following the downstream movement of the turbine, from a sealing position in which it at least partly surrounds the upstream rim of the blading and bears radially on this upstream rim, and a tilted position in which it is axially spaced from the upstream rim of the blading, and - the overspeed limitation device comprises at least one projectile housed in said space and configured to be released into the turbine when the first element moves from its release position to its tilted position.

[0017] Thus, the turbomachine as described allows the low-pressure turbine to be stopped in the event of a rupture of an element of the turbomachine and the displacement of the low-pressure rotor, for example the shaft connecting the low-pressure rotor to the reducer, or an internal member of the reducer, or the shaft connecting the reducer to the fan, thanks solely to a mechanism that is activated autonomously by simple recoil of the turbine following the rupture of the element of the turbomachine. The overspeed phenomenon can be avoided or limited. It will then be understood that it is not necessary to use an overspeed detection device. The turbomachine as described is therefore an integrated safety or "fail-safe" system that uses the recoil of the turbine to limit the overspeed phenomenon.Another advantage of the invention is that it makes it possible to dispense with a complex control system for controlling the seal, this seal being achieved autonomously via a mechanical interaction between the sealing device and a blade having an external upper end without wipers.

[0018] Furthermore, the speed with which the limiting device slows the rotor now depends only on its response time after the turbine recoils. Furthermore, the device makes it possible to project a free projectile through several successive stages, and, the characteristics of the projectile being calculated, to predict with certainty the destruction of all these stages. The major advantage is that it is no longer necessary to sacrifice the performance of a distributor stage to ensure overspeed stopping. It is therefore possible to maintain an efficient aerodynamic design while meeting the certification point.

[0019] The invention may further comprise one or more of the following optional features, in any technically possible combination: - the first element is mounted so as to tilt or pivot relative to axes tangent to a circumference centered on the longitudinal axis; - in the tilted position, the downstream end of the first element is oriented radially downstream and inwards; - the first element is an upstream element of the sealing device; - the sealing device further comprises a second downstream annular element attached to the downstream end of the first element and comprising an internal annular surface arranged opposite a portion of the external periphery of the blading; - the first and second elements are fixed to an internal annular surface of the casing by means of at least one elastic member; - the overspeed limitation device further comprises a system for propelling the projectiles out of said space, said system being configured to be triggered automatically when the first element tilts; - the propulsion system comprises at least one elastic member; - the at least one elastic member is configured to stress the first and second elements radially inwards and resting on the external periphery of the blading, in order to provide a seal; - the at least one projectile is a ball or a cross, for example metallic.

[0020] The invention also relates to a method for limiting overspeed in a turbomachine of the present invention.

[0021] The overspeed limitation method comprises: - a step of displacement of the turbine rotor, downstream along the longitudinal axis, following a rupture of an element of the turbomachine, - a step of tilting the sealing device in response to the moving step, during which the first element of the sealing device tilts from the sealing position to the tilted position; - a release step in response to the switching step, during in which the overspeed limiting device causes the release of at least one projectile into the turbine. Brief description of the figures

[0022] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which: - [Fig.l] is a very schematic half-view in longitudinal section of a conventional turbomachine ..., - [Fig.2] is a half-detailed view in longitudinal section of a turbine low pressure equipped with a sealing device according to a prior state of the art; - [Fig.3] is a half-detailed view in longitudinal section of a turbine low pressure equipped with an overspeed limitation device according to a prior state of the art; ... - [Fig.4] is a partial schematic view in longitudinal section of a turbomachine turbine according to the invention; - [Fig.5] is a partial schematic detail view of a portion of the turbine according to [Fig.4] showing the sealing and speed limiting devices according to the invention; - Figure 6 is a partial longitudinal sectional view of a low-pressure turbine of the turbomachine according to the invention, equipped with the sealing device according to an embodiment of the invention shown in an inactive mode; - Figure 7 is a partial longitudinal sectional view of a low-pressure turbine of the turbomachine according to the invention, equipped with the sealing device according to an embodiment of the invention shown in an active mode; - [Fig.8] is a partial longitudinal sectional view of a base turbine pressure of the turbomachine according to the invention, equipped with the overspeed limitation device according to an embodiment of the invention shown in an inactive mode; - [Fig.9] is a partial longitudinal sectional view of a base turbine pressure of the turbomachine according to the invention, equipped with the overspeed limitation device according to an embodiment of the invention shown in an active mode; - [Fig. 10] is a simplified schematic view of a released projectile entering contact with a moving blade and a fixed blade, according to a variant; and - [Fig. 11] is a simplified schematic view of the projectile of [Fig. 10] entering into rotation after contact with a moving blade and a fixed blade. Detailed description of the invention

[0023] In the following description, identical reference numerals designate identical parts or parts having similar functions. The designations "upstream" and "downstream" are defined with respect to a direction of flow of gases inside a turbomachine. The axial direction corresponds to the direction of the axis of the turbomachine, and a radial direction is a direction perpendicular to the axis of the turbomachine and intersecting this axis. The adjectives "inner" and "outer" are used with reference to a radial direction so that the inner part of an element is, in a radial direction, closer to the axis of the turbomachine than the outer part of the same element.

[0024] [Fig. 1] illustrates, for example and in a non-limiting manner, a type of aircraft turbomachine 100 to which the invention applies and which is here a double-flow, double-spool turbojet. The overall architecture of this turbomachine 100 is a conventional two-spool architecture, known from many turbomachines of the state of the art. For this reason, in the remainder of this description, any reference to the general architecture of a turbomachine according to the state of the art will be made by considering [Fig. 1].

[0025] Essentially, the turbomachine 100 comprises, from upstream to downstream according to the direction of flow of the gas flows F in the turbomachine, a fan 114 provided with blades 116, a low-pressure compressor 104BP, a high-pressure compressor 104HP, an annular combustion chamber 106, a high-pressure turbine 102HP, a low-pressure turbine 102BP and an exhaust turbine 110.

[0026] A 304HP rotor of the 104HP high-pressure compressor and a 202HP rotor of the 102HP high-pressure turbine are connected by a 108HP high-pressure shaft and form with it a high-pressure body. A 304BP rotor of the 104BP low-pressure compressor and a 202bp rotor of the 102BP low-pressure turbine are connected by a 108bp low-pressure (LP) shaft and form with it a low-pressure body.

[0027] Still with reference to [Fig.l], in the upstream part of the turbomachine 100, the fan 114 is connected to a fan shaft 118 which, in the example shown, is linked in rotation to the LP shaft 108BP by means of a reducer 120, for example a planetary reducer, which has been shown here schematically. The fan 114 and the low-pressure compressor 104BP thus form a low-pressure upstream module of the turbomachine 100.

[0028] In certain engines, the fan 114, and in particular when it is very large, is driven at a rotation speed lower than that of the LP shaft 108BP, in order to better adapt it aerodynamically.

[0029] The HP 108Hp and BP 108Bp shafts extend along a longitudinal axis A of the turbomachine 100.

[0030] The turbomachine 100 also comprises a fan casing (not visible) which extends around the blades 116 and which defines an air inlet vein for the flows F in the turbomachine. A portion of this air enters an internal annular flow vein 112 for a primary flow and the other portion feeds an external annular flow vein (not visible) for a secondary flow. The vein 112 passes through the low-pressure 104BP and high-pressure 104HP compressors, the combustion chamber 106 and the high-pressure 102HP and low-pressure 102BP turbines. The external vein envelops the casings of the compressors and turbines and joins the internal vein 112 in a nozzle (not shown) of the turbomachine 100.

[0031] The fan shaft 118 114 and the low pressure shaft 108BP are centered and guided in rotation around the axis A by bearings 122b 1222, 1223 located upstream of the turbomachine 100.

[0032] The shaft 118 of the fan 114 can be guided either by two tapered roller bearings 122b 1222 or by two roller and ball bearings 122b 1222 respectively.

[0033] As for the low pressure shaft 108BP, it is guided in its upstream part by at least one ball bearing 1223 which forms an axial stop conditioning the axial position of the corresponding LP shaft 108BP in operation.

[0034] In the case of a breakage of the BP shaft 108BP, the recoil of the low-pressure shaft 108BP can be used to counter the risk of overspeed. Indeed, in the case of such a breakage, the downstream part of the BP shaft 108BP is no longer retained by the ball bearing 1223 located upstream of the BP shaft 108BP and is therefore free to recoil axially. Overspeed limiting devices have therefore been proposed which make it possible to use this recoil to slow down the BP shaft 108BP.

[0035] Thus, in a turbomachine configuration similar to that of the turbomachine of [Fig.l], devices are taught for destroying the moving blades of a given 204BP blade of the 102BP turbine in order to slow it down or stop it, according to a technique called “feathering” of the 102BP LP turbine.

[0036] [Fig. 2] illustrates a partial view of a 102BP LP turbine. In this example, the 102BP LP turbine comprises, in a non-limiting manner, at least two stages of blades, each comprising a 204BP moving rotor blade. Upstream of each 204BP moving rotor blade, a corresponding 206bp stator or rectifier blade is arranged.

[0037] The BP 102BP turbine further comprises a stator casing 200BP which surrounds the moving blades 204BP and the stator blades 206BP.

[0038] The turbine may also include a sealing device 208 carried by the casing. at its internal Sic surface. The sealing device is configured to cooperate with a ferrule 404, located at an upper or external end of a mobile blade 204BP and provided with wipers in order to ensure the sealing of the turbine.

[0039] The sealing device 208 generally consists of a support on which an abradable coating is fixed. It is the clearance control between the wipers 408 and the abradable coating which ensures the sealing of the turbine. This control is generally managed by a complex sealing control system.

[0040] According to the plumage technique, illustrated in [Fig. 3], an overspeed destruction or limitation device 210 comprises obstacle means Sb which are arranged on a stator blading 206Bp of the low pressure turbine 102BP. These obstacle means Sb consist of domed zones Sb of guide vanes 401 of the stator blading 206BP. Each blade 401 is arranged with a clearance J relative to the associated rotor blading 204BP. The domed areas Sb are designed, in the event of the BP shaft 108BP moving back, resulting in a reduction in the clearance J, to be arranged on the path of the moving blades 400 of the rotor blade 204BP and thus come into contact with the moving blades 400 of the blade 204BP of the low pressure rotor 202BP to destroy the moving blades 400 and thus slow down and then stop the rotation of the low pressure turbine 102BP.The BP 108 BP shaft is then no longer driven by the highly energetic gases coming from the combustion chamber and therefore does not risk being in overspeed.

[0041] However, there is currently no effective solution for preventing overspeed of the BP shaft 108BP in the event of breakage of the fan shaft 114 or in the event of breakage of an internal component of the reducer 120.

[0042] Indeed, in this case, the BP 108BP shaft is still held axially by its ball bearing 1223, so that it is not able to move backward, and the aforementioned braking or “feathering” technologies are ineffective.

[0043] Such an overspeed can cause a burst of the stator blades 206BP (or fixed blades) of one or more stages of the LP turbine 102BP. Indeed, by construction, the LP turbines comprise, in a known manner, for each stage blades secured to the turbine disks. These disks are designed to radially retain the blades, are subjected to very intense centrifugal forces and are dimensioned to withstand them up to a certain speed, beyond which they risk bursting. The bursting of a disk is likely to cause the sending of high-energy debris from disks and blades mainly in a radial direction, this debris then being able to pass through the casings of the turbomachine, or even the wings or the cabin of the aircraft to which the turbomachine 100 belongs, with high consequences for its safety.

[0044] Such an overspeed could also be detrimental to the reducer 120, which is not sized to withstand overspeed regimes of the BP shaft 108BP.

[0045] With reference to Figures 4 to 11, the solution proposed by the invention will now be described.

[0046] The turbomachine of the present invention has a general structure similar to the turbomachine described in [Fig.l]. Its description will therefore be made partly with reference to [Fig.l].

[0047] Thus, the turbomachine 100 comprises at least one compressor 104BP, 104HP, an annular combustion chamber 106 and at least one turbine 102BP, 102HP. The turbine 102bp, 102hp comprises at least one rotor 202BP, 202HP connected by a shaft 108BP, 108HP to a rotor of the compressor 304BP, 304HP. The rotor of the turbine 202BP, 202HP comprises at least one moving blade 204BP, 204HP surrounded by a stator casing 200BP, 200HP of the turbine.

[0048] In particular, the low pressure (LP) turbine 102BP of the turbomachine 100 of the present invention may comprise a plurality of stages of moving blades 204BP and fixed blades 206BP.

[0049] In [Fig.l], a 102BP LP turbine is shown comprising three stages of blades, each stage comprising a rotor blade or moving blade 204BP and a stator blade or fixed blade 206BP but, it will be understood that this arrangement is not limiting of the invention.

[0050] The high pressure (HP) turbines 102HP and BP 102BP are each housed in a corresponding HP turbine casing 200HP and BP turbine casing 200BP, which carry corresponding fixed stages of distributors 206BP, 206BP interposed between the stages of moving blades 204HP, 204BP. Downstream of the BP turbine casing 200BP, an exhaust casing 110 allows the evacuation of the gases having passed through the turbomachine 100, that is to say having circulated in the primary flow path 112 of the turbomachine 100. An inter-turbine casing 200inter is arranged between the HP turbines 102HP and BP 102BP, and more particularly between the HP turbine casing 200HP and the BP turbine casing 200BP.

[0051] The turbomachine 100 shown in [Fig.l] is a double-spool turbomachine, but it will be understood that the invention which will now be described also finds application to a multi-spool turbomachine, for example a three-spool turbomachine comprising an additional intermediate body, and therefore comprising an additional turbine and an additional associated turbine casing.

[0052] [Fig.4] illustrates a portion of a 102BP low pressure turbine according to the invention.

[0053] According to the invention, the low-pressure turbine 102BP comprises an annular sealing device 208 carried by the casing 200BP and which extends around a longitudinal axis A of the turbomachine 100. The casing 200BP surrounds stages of moving blades 204BP and carries fixed blades 206BP interposed between the stages of moving blades 204BP. In the example given, the turbine portion comprises two stages, each stage comprising a rotor blade or moving blade 204BP and a stator vanes or fixed vanes 206Bp.

[0054] The turbine further comprises an overspeed limitation device 210 in the event of rupture of an element of the turbomachine, for example the LP shaft 108Bp.

[0055] Unlike the solution of the prior art, in particular that of the "feathering" technique described above, where the overspeed limiting device is arranged on the fixed blading 206BP, the overspeed limiting device 208 of the present invention is arranged at the level of the mobile blading 204BP.

[0056] With reference to [Fig. 5], the annular sealing device 208 comprises at least one first annular element 600i carried by the casing 200BP and which is capable of coming to bear radially inwards on an annular rim 406 upstream of the external periphery of the blading 204BP.

[0057] The first annular element 600i comprises or defines an annular space or housing 802 which extends radially between this element 600i and the casing 200BP.

[0058] The sealing device 208 further comprises a pivot which can be carried by the casing and which is disposed at an upstream end of the first element 600i.

[0059] Thus, the first element 600i is mounted so as to tilt or pivot relative to axes tangent to a circumference centered on the longitudinal axis A.

[0060] The sealing device 208 further comprises a second downstream element 6002 disposed downstream of the first element 600i. The upstream end of the second element 6002 is attached to the downstream end of the first element 600i.

[0061] The second element comprises an internal surface SE0 arranged opposite at least a portion of the external periphery of the blading 204BP. As can be seen in [Fig.5], the shell 404 represents the external periphery of the blading 204BP and the internal surface SE0 is positioned opposite the external surface SVi of the shell 404 of a moving blade 400 of the moving blading 204BP.

[0062] The first 600i and second 6002 elements are fixed to the internal surface Slc of the casing 200bp, by means of at least one elastic member 604b 6042 shown here and in FIGS. 6 to 9, in a non-limiting manner, by a spring. The elastic member 604b 6042 is configured to urge the first and second elements radially inward and bearing on the external periphery of the blading, in order to seal the turbine 102BP. The intensity of the stress can thus be predetermined in order to effectively control the sealing of the turbine 102BP.

[0063] Still with reference to [Fig. 5], the overspeed limitation device 210 comprises free projectiles 800 which are housed in the annular space or housing 802 defined between the first sealing element 600i and the casing 200BP. The projectiles are configured to be released into the turbine 102BP when the first element 600i passes from a release position, where its downstream edge is no longer in contact with the upstream annular rim 406 of the outer periphery of the blading 204BP, to a tilted position, where its upstream edge is oriented inwards, as will be seen in the examples in Figures 8 and 9.

[0064] The overspeed limitation device 210 further comprises a system 804 for propelling the projectiles out of the annular space or the housing 802. The propulsion system is configured to be triggered automatically when the first element 600i of the sealing device 208 tilts.

[0065] The propulsion system 804 may comprise at least one elastic member 806, as illustrated in [Fig.9], configured to provide the thrust necessary to expel the projectiles from the annular space or the housing 802.

[0066] It will be understood, in all embodiments of the invention, that each projectile 800 has characteristics of mass, dimension, hardness, and shape, capable of allowing a release of energy upon its impact with the blades 400 of the stages 204BP, which is sufficient to cause the blades 400 to break. For example, it is possible to design projectiles 800 having particular spherical or, on the contrary, angular shapes, capable of promoting the breakage of the blades of the stages 204Bp.

[0067] The projectiles 800 are, for example, and in a non-limiting manner, balls, as shown in [Fig. 5], or metal crosses, as illustrated in Figures 10 and 11.

[0068] In the preferred embodiment of the invention, the overspeed limitation device 210 is mounted upstream of at least two stages of the LP turbine 120BP so that the free projectiles 800 and the blade debris of at least one upstream stage cause the destruction of at least one downstream stage.

[0069] With reference to Figures 6 and 7, the production of the sealing of the turbine 102BP according to the invention will now be described.

[0070] As illustrated in [Fig.6], the elastic members 604b 6042, respectively of the first and second elements 600i, 6002, fixably press the first and second elements 600i, 6002 onto the top of the shroud 404, without lickers, of a moving blade 400 of the moving blade 204BP. More precisely, the first element 600i is pressed onto the annular rim or heel 406 of the shroud and the second element 6002 onto the remainder of the external surface SVide the shroud 404.

[0071] The first and second elements 600i, 6002 and the external surface Svi of the ferrule 404 are separated by a clearance of the order of a few millimeters.

[0072] The first element and the second element, which make up the sealing device, can be configured so as to have an aerodynamic shape allowing passage of the air flow F in the clearance defined between the first and second elements 600i, 6002 and the external surface Svi of the shroud 404 of the moving blade 400.

[0073] This configuration makes it possible to achieve sealing of the turbine via an effect venturi. Indeed, with reference to [Fig.7], the reduction in section between the first and second elements 600i, 6002 and the external surface SVi of the shell 404 causes an acceleration of the passage of air.

[0074] The first element 600i above which the projectiles 800 are arranged does not change position or very little with respect to the annular rim 406 of the ferrule 404. The second 6002 which does not carry projectiles 800 moves radially away from the ferrule 404. This difference is due to the acceleration of the passage of the air which increases the lift of the second element 6002, exerting a force Fi opposed to the stress of the elastic member and promoting the opening or enlargement of the clearance between the second element 6002 and the ferrule 404.

[0075] Conversely, the opening of the clearance has the effect of slowing down the air flow F, which reduces the lift and promotes the closing or reduction of the clearance between the sealing device and the external surface Svi of the shroud 404 of the blade.

[0076] The intensity of the stress can thus be predetermined in order to effectively control the clearance between the sealing device and the blades, and therefore to control the air leakage flow rate.

[0077] Advantageously, those skilled in the art will understand that the sealing is achieved autonomously via a mechanical interaction or collaboration between the sealing device as described in the present invention and a blade having an upper end without wipers. The solution thus described makes it possible to dispense with a complex control system which may include computerized means for controlling the sealing as taught in the prior art.

[0078] With reference to [Fig.8] and 9 the overspeed limitation according to the invention will now be described.

[0079] [Fig.8] illustrates a phase of recoil of the mobile 204BP BP turbine and a release of the first sealing element.

[0080] In the event of recoil or axial displacement of the rotor of the LP turbine 102BP, represented by the arrow R, following the rupture of an element of the turbomachine, the downstream end of the first element of the sealing device is released by the mobile blade 204BP, that is to say that the downstream end of the first element is no longer in support on the annular rim 406 of the shroud 404 of the mobile blade 400 of the blade 204BP.

[0081] With reference to [Fig.9], the first element 600i which is movable around the pivot 602 then tilts, after release, from a sealing position PI (represented by dotted lines) in which it at least partly surrounds the upstream edge of the blading and is in radial support on this upstream edge, and a tilted position P2 (represented by dotted lines) in which it is axially spaced from the upstream edge of the blading 204BP.

[0082] In the tilted position P2, the downstream end of the first element 600i is oriented radially downstream and inwards relative to the annular rim or the end upstream 406 of the shroud 404 of the blade 400 of the mobile blade 204BP.

[0083] The tilting of the first element 600i automatically triggers the propulsion system which expels the projectiles from the annular space or housing 802 defined between the first element 6001 and the casing 200Bp. The projectiles are then released upstream of the mobile blade 204BP, causing at least its destruction and the stopping of the turbine 102BP.

[0084] Advantageously, those skilled in the art will understand that the overspeed limitation solution described above allows at least the stopping of the low-pressure turbine in the event of a rupture of an element of the turbomachine, and thus avoids or limits the overspeed phenomenon, with only a mechanical system making it possible to do without an overspeed detection device. The proposed solution also makes it possible not to impact the aerodynamic design of the vein parts such as the modification of the stator blading in a prior art solution of the “feathering” type and therefore to preserve the performance of the turbomachine 100.

[0085] Figures 10 and 11 illustrate a scenario of destruction of mobile blades 204BP and fixed blades 206BP by the released projectiles, according to a variant.

[0086] In [Fig. 10], which illustrates a simplified schematic top view of a 102BP low pressure turbine, two blades are shown, one of stator 206BP or fixed blades and the other of rotor 204BP or moving blades.

[0087] The air flow F is oriented from upstream to downstream along a longitudinal axis A of the turbomachine 100. The mobile stages rotate around the longitudinal axis A in the direction, represented by the arrow SR, counterclockwise.

[0088] The projectile 800 in this example is cross-shaped. This shape can be optimized or configured to effectively destroy the blades.

[0089] The projectile 800 comprises at least small branches and large branches. The small branches are configured to have a total length Lp slightly greater than the inter-blade distance. Depending on the length Lg of the large branches, the projectile may be configured to take a slightly curved shape to accommodate the radius of the low-pressure turbine, in which the projectile is housed. This configuration of the projectile allows contact between the projectile and the blades of the rotor 204BP and stator 206BP blades as illustrated in [Fig. 10].

[0090] With reference to [Fig. 11], the projectile in contact with the blades of the rotor 204BP and stator 206BP blades causes the assembly to rotate, the large branches blocking the rotation of the rotor blades and causing the destruction thereof. For example, and in a non-limiting manner, the housing 802 between the first element 600i and the casing 200BP of the turbine 120BP may contain between three and eight such projectiles, preferably eight, to effectively destroy the rotor 202BP.

[0091] Thus, the housing 802 can be configured to receive a predetermined number of projectiles that can effectively destroy the 202BP rotor.

[0092] It is also possible in certain embodiments to combine different types of projectiles and different shapes to improve the destruction of the rotor and limit overspeed. For example, and in a non-limiting manner, the overspeed limiting device may comprise projectiles comprising balls and crosses such as those mentioned in the description.

[0093] The invention also relates to a method for limiting overspeed in a turbomachine as described in the present invention.

[0094] The overspeed limitation method comprises at least one step of moving or moving back the rotor 202BP of the turbine (102BP) of the turbomachine (100), downstream along the longitudinal axis of the turbomachine (100). This movement or following the breakage of an element of the turbomachine, for example, and in a non-limiting manner, of the LP shaft 108BP.

[0095] The method further comprises a step of tilting the sealing device 208 in response to the moving step. In this step, the first element 600i of the sealing device 208 tilts from a sealing position PI, in which it at least partially surrounds the upstream rim of the blading and is in radial support on this upstream rim, to a tilted position P2, in which it is axially spaced from the upstream rim of the blading 204BP. The first element 600i of the sealing device 208 has its upstream end released, that is to say that this end is no longer in support on the annular rim of the upper end of the mobile blading 204BP.

[0096] The method further comprises a step of releasing in response to the tilting step, during which the overspeed limiting device (210) causes the release of at least one projectile 800 into the turbine 102BP. In this phase, the propulsion system 804 propels the projectiles into the LP turbine 102BP upstream of a moving blade 204BP.

[0097] The release of projectiles in the turbine destroys or breaks the rotor which breaks and stops due to the interaction of the released projectiles 800 in the turbine and the moving and / or fixed blades. Indeed, the free projectiles 800 cause the blades of a moving blade 204BP of a first stage of the turbine to break and the projectiles 800 accompanied by the blade debris cause the destruction of all the stages located downstream of the first stage, until the blades of the LP turbine 102BP are completely destroyed.

[0098] Although the invention has been described in relation to a particular type of turbomachine, it will be understood that it could be applied to any other type of turbomachine.

Claims

Claims

1. A turbomachine (100), in particular an aircraft turbomachine, comprising at least one compressor (104BP), an annular combustion chamber (106) and at least one turbine (102Bp), the turbine (102BP) comprising a rotor (202BP) connected by a shaft (108BP) to a rotor of the compressor (304BP), the rotor of the turbine (202BP) comprising at least one blading (204BP) surrounded by a stator casing (200BP) of the turbine, and the turbine (102BP) comprising an annular sealing device (208) carried by the casing (200BP) and which extends around a longitudinal axis (A) of the turbomachine (100), said sealing device (208) cooperating with an external periphery (404) of the blading (204BP), the turbomachine (100) further comprising a device for limiting overspeed (210) of said shaft (108BP), the rotor of the turbine (102BP) being intended to move downstream along the longitudinal axis (A) in the event of rupture of an element of the turbomachine, characterized in that: - the annular sealing device (208) comprises at least one first annular element (6000) which is capable of bearing radially inwards on an annular rim (406) upstream of the external periphery (404) of the blading (204BP), this first annular element (6000) comprising or defining an annular space (802) which extends radially between this first annular element (6000) and the casing (200BP), this first annular element (6000) being carried by the casing (200 BP) and movable in tilting, following the downstream movement of the rotor of the turbine (102BP), from a sealing position (PI) in which it at least partly surrounds the upstream rim of the blading and is in radial support on this upstream rim, and a tilted position (P2) in which it is axially spaced from the upstream rim of the blading (204BP), and - the overspeed limiting device (210) comprises at least one projectile (800) housed in said space (802) and configured to be released into the turbine (102BP) when the first annular element (6000) passes from a release position to its tilted position.

2. A turbomachine (100) according to claim 1, wherein the first annular element (6000 is mounted so as to tilt or pivot with respect to axes tangent to a circumference centered on the longitudinal axis (A).

3. Turbomachine (100) according to any one of claims 1 or 2, in which, in the tilted position (P2), the downstream end of the first annular element (6000) is oriented radially downstream and inwards.

4. Turbomachine (100) according to any one of the preceding claims, in which the first annular element (6000 is an upstream element of the sealing device (208).

5. Turbomachine (100) according to any one of the preceding claims, in which the sealing device (208) further comprises a second downstream annular element (6002) attached to the downstream end of the first annular element (600i) and comprising an internal annular surface (Seo) arranged opposite a portion of the external periphery of the blading (204Bp).

6. Turbomachine (100) according to claim 5, in which the first (600i) and second (6002) annular elements are fixed to an internal annular surface (Slc) of the casing (200Bp) by means of at least one elastic member (604i, 6042).

7. Turbomachine (100) according to any one of the preceding claims, in which the overspeed limitation device (210) further comprises a system (804) for propelling the projectiles out of said space (802), said system (804) being configured to be triggered automatically when the first annular element (600i) tilts.

8. Turbomachine (100) according to the preceding claim, in which the propulsion system (804) comprises at least one elastic member (806).

9. Turbomachine (100) according to claim 6, in which the at least one elastic member (604b 6042) is configured to urge the first (600i) and second (6002) annular elements radially inwards and bearing on the external periphery (404) of the blading (204BP), in order to provide sealing.

10. Turbomachine (100) according to any one of the preceding claims, in which the at least one projectile (800) is a ball or a cross, for example metallic.

11. Method for limiting overspeed in a turbomachine according to one of of the preceding claims, comprising: - a step of moving the rotor of the turbine (102BP), downstream along the longitudinal axis, following a rupture of an element of the turbomachine; - a step of tilting the sealing device (208) in response to the displacement step, during which the first element of the sealing device tilts from the sealing position (PI) to the tilted position (P2); - a release step in response to the tilting step, during which the overspeed limiting device (210) causes the release of at least one projectile (800) into the turbine (102BP).