Turbine nozzle guide vane comprising an annular sealing element

Abstract

The present invention relates to a nozzle guide vane (3) for a turbine (2), having an axis (X) of revolution and comprising: - a flange (6) extending radially relative to the axis (X); - a ring seal (12) mounted on the flange and comprising an inner face (15a) that is configured to bear an abradable element (13); - a ventilation cavity (17) delimited radially on the inside by an outer face (15b) of the ring seal (12) and downstream by an upstream face (6a) of the flange (6); - a baffle configured to guide an airflow toward the ventilation cavity (17); and - at least one through-opening (20) formed in the ring seal (12) and configured to put the ventilation cavity (17) in fluidic communication with the inner face (15a) of the ring seal (12).

Description

FIELD OF THE INVENTION

[0001] The invention relates to a turbojet and more generally to a turbomachine comprising a distributor having a radially internal face carrying an annular sealing element of a labyrinth-type seal, this annular sealing element being made of an abradable material intended to cooperate with wipers carried by a rotor opposite this annular sealing element. STATE OF THE ART

[0002] A turbomachine generally comprises, from upstream to downstream in the direction of gas flow through the turbomachine, a fan, one or more compressor stages, for example a low pressure compressor and a high pressure compressor, a combustion chamber, one or more turbine stages, for example a high pressure turbine and a low pressure turbine, and a gas exhaust nozzle 8.

[0003] In a manner known per se, the turbines are produced in the form of a succession of stages each comprising a wheel of moving blades (rotor) rotating in front of a wheel of fixed blades (stator, or distributor) configured to convert combustion energy into motive energy, in particular to drive the compressor stages and the fan. The rotor disks of the turbine are centered on a longitudinal axis X of the turbomachine and are generally assembled together by means of shrouds on the upstream disk and the downstream disk. Each distributor comprises a plurality of fixed blades distributed circumferentially around the axis.

[0004] The distributor includes fixed vanes configured to accelerate and deflect a flow of combustion gas toward the moving vanes immediately downstream.

[0005] It is known to arrange a dynamic seal radially inside the distributors in order to reduce the circulation of gases outside the primary annular duct in which the fixed and moving blades extend. Such a seal generally comprises a sealing ring carrying an abradable element integral with the distributor and one or more wipers integral with the rotor.

[0006] During turbojet operation, the distributor is exposed to higher temperatures than the rotor disc and the thermal inertia of the distributor is generally lower than that of the disc, which leads to a variation in the clearance between the sealing ring and the wipers. This results in an increase in the leakage flow rate when the aforementioned clearance increases and an acceleration of the wear of the abradable element when this clearance decreases.

[0007] Document FR 3 027 343 discloses a mounting solution allowing radial movement between the sealing ring and the distributor. However, the sealing of such an assembly is sensitive to temperature variations because the expansion of the sealing ring causes an opening of the clearances between the abradable element and the facing wipers, which deteriorates the performance of the engine. However, the cooling flow injected between the abradable element and the wipers does not mix with the hot air coming from the flow stream which leaks between the distributor and the immediately adjacent rotating disc, which makes the temperature variations of the freely expanding sealing ring depend on the leakage flow of the hot air from the flow stream.In transient phases, this results in a sealing ring that expands under the effect of the increase in temperature, which results in the opening of the seal gaps, an increase in their permeability and therefore a reduction in the performance of the seal.

[0008] Finally, the temperature difference of the upstream and downstream ventilation cavities (on either side of the sealing ring) is substantial, which causes a temperature difference between the ring mounting flanges and creates differential thermal expansion which can block the radial movement of the sealing ring relative to the distributor.

[0009] Document FR 3 107 298 describes a dispenser in accordance with the preamble of claim 1. STATEMENT OF THE INVENTION

[0010] An aim of the invention is to remedy the aforementioned drawbacks by proposing a distributor comprising a seal whose performance is less sensitive to temperature variations, in particular when the seal comprises a sealing ring mounted with radial clearance on the distributor, and whose service life is improved.

[0011] For this purpose, according to a first aspect of the invention, a turbine distributor is proposed having an axis of revolution and comprising: a flange extending radially relative to the axis; a sealing ring mounted on the flange and comprising an inner face configured to carry an abradable element; a ventilation cavity delimited radially on the inside by an outer face of the sealing ring and downstream by an upstream face of the flange; a deflector configured to guide an air flow towards the ventilation cavity, the deflector being fixed on a bent upstream edge of the sealing ring which extends radially inwards; and at least one through-orifice formed in the sealing ring and configured to put the ventilation cavity in fluid communication with the inner face of the sealing ring.

[0012] Some preferred but non-limiting features of the dispenser according to the first aspect are the following, taken individually or in combination: the deflector is mounted on one of the flange and the sealing ring so as to extend substantially radially into the ventilation cavity; the deflector is fixed on an upstream bent edge of the sealing ring; the upstream edge extends radially inward; the distributor comprises a bent sheet metal fixed on an upstream edge of the sealing ring, the at least one orifice passing through the deflector; the deflector comprises a substantially flat or frustoconical sheet metal; the deflector extends radially relative to the axis; the deflector is brazed to one of the flange and the sealing ring or is monolithic with the sealing ring; and / or the sealing ring is mounted to be movable radially relative to the flange.

[0013] According to a second aspect, the invention provides a turbine comprising a distributor according to the first aspect.

[0014] According to a third aspect, the invention proposes a turbomachine comprising a turbine according to the second aspect and an additional turbine, a rotational speed of the additional turbine being greater than a rotational speed of the turbine.

[0015] According to a fourth aspect, the invention proposes an aircraft comprising a turbomachine according to the third aspect. DESCRIPTION OF FIGURES

[0016] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which: There figure 1 is a sectional view of an example of a turbine comprising a distributor according to an embodiment of the invention, on which the different fluids (gases) circulating under the distributor have been schematically represented; The figure 2is a partial perspective view of an example of a sealing ring and deflector according to an embodiment of the invention; figure 3 is a sectional view of an example of a conventional turbine comprising a distributor on which the different fluids circulating under the distributor have been schematically represented; and The figure 4 illustrates an aircraft comprising two turbomachines in accordance with one embodiment of the invention.

[0017] Throughout the figures, similar elements have identical references. DETAILED DESCRIPTION OF THE INVENTION

[0018] In the present application, upstream and downstream are defined relative to the normal flow direction of the gases in the turbomachine 1 (in particular of an aircraft 100), and therefore along the nozzle 3 of the low-pressure turbine 2. Furthermore, the X axis of the nozzle 3 is called the X axis around which the nozzle 3 extends, which corresponds to the X axis of revolution of the rotor 7 of the turbine 2. An axial direction corresponds to the direction of the X axis, a radial direction is a direction perpendicular to this X axis and passing through it. Furthermore, a circumferential direction corresponds to a direction perpendicular to the X axis and not passing through it. Unless otherwise specified, internal (or interior) and external (or exterior), respectively, are used with reference to a radial direction so that the internal part or face of an element is closer to the X axis than the external part or face of the same element.

[0019] In a manner known per se, a distributor 3, in particular of a low-pressure turbine 7, comprises a shroud 4 provided with a plurality of fixed blades 5 distributed circumferentially around the shroud 4. The shroud 4 comprises in particular a flange 6 which extends radially inward relative to the blades 5.

[0020] The distributor 3 may be sectorized and comprise a plurality of distributor sectors 3 fixed together end to end around the X axis. Alternatively, the distributor 3 may be formed integrally and in one piece, in which case the distributor sectors 3 are monolithic.

[0021] The turbine 2 further comprises a rotor 7 comprising a plurality of discs 8 each comprising a rim 9 and blades 10. The blades 10 are attached and fixed in cells 11 formed in the rim 9 of the corresponding disc 8 and extend radially from the rim 9.

[0022] The distributor 3 extends between two adjacent discs 8 of the rotor 7 of the turbine 2. Preferably, the turbine 2 comprises a succession of stages each comprising a disc 8 of the rotor 7 rotating in front of an associated distributor 3.

[0023] The turbine 2 further comprises a seal comprising a sealing ring 12 connected to the flange 6 by a sliding connection and configured to carry a first sealing element 13, and a second sealing element 14 configured to cooperate with the first sealing element 13 which may for example be carried by a support fixed between the two adjacent discs 8 of the rotor 7 of the turbine 2. The first sealing element 13 may comprise an abradable element 13, such as a honeycomb structure, fixed on the inner face 15a of the ring 12. The second sealing element 14 may then comprise wipers 14 extending radially from the support. In the following, an example of a seal comprising an abradable element 13 and wipers 14 will be described. This is however not limiting, the invention being able to apply to seals comprising other sealing elements.

[0024] More precisely, the flange 6 extends substantially radially from the shell 4 in the direction of the second sealing elements (i.e. opposite the blades) and has an upstream face 6a and a downstream face 6b, substantially radial.

[0025] The sealing ring 12 can be attached and connected to the flange 6 by a sliding connection. It comprises a metal sheet comprising an axial portion 15 and a radial portion 16. The axial portion 15 has the internal face 15a configured to receive the abradable element 13, and an external face 15b opposite the internal face 15a which is configured to extend facing the shell 4. The abradable element 13 is fixed directly on the internal face 15a of the axial portion 15. The axial portion 15 further has an upstream edge 15c and a downstream edge 15d.

[0026] The radial portion 16 extends from the external face 15b of the axial portion 15 and is configured to be mounted on the flange 6. The radial portion 16 may in particular be centered relative to the axial portion 15.

[0027] In one embodiment, the radial portion 16 is mounted on the flange 6 so as to allow radial clearance between the sealing ring 12 and the flange 6. For this purpose, the radial portion 16 may comprise an upstream flange 16a and a downstream flange 16b configured to come into contact with the upstream face 6a and the downstream face 6b, respectively, of the flange 6. Reference may be made to document FR 3 027 343 for further details on the mounting with radial clearance of the sealing ring 12 on the flange 6.

[0028] The ring 12 and the flange 6 together define an upstream ventilation cavity 17 and a downstream ventilation cavity 18. The upstream cavity 17 is delimited upstream by the rotating disc 8 of the rotor 7 immediately upstream, downstream by the upstream face 6a of the flange 6, radially on the inside by the external face 15b of the axial part of the ring 12 and radially on the outside by the internal face of the shell 4. The downstream cavity 18 is delimited upstream by the downstream face 6b of the flange 6, downstream by the rotating disc 8 of the rotor 7 immediately downstream, radially on the inside by the external face 15b of the axial part of the ring 12 and radially on the outside by the internal face of the shell 4.

[0029] The mounting with play of the ring 12 on the flange 6 allows the passage of air (zone 16c) between the plates 16a, 16b of the ring 12 and the flange 6, which places the upstream 17 and downstream 18 cavities in fluid communication and facilitates their ventilation.

[0030] In a manner known per se, a flow of cooling gas F1 (coming in particular from an upstream part of the turbomachine 1, for example from a compressor section) passes through the bottom of the cells 11 and is injected between the abradable element 13 and the lips 14 of the seal in order to cool the seal and ensure its sealing.

[0031] Furthermore, gases F2 may leak at the external surface of the rim 9 of the disc 8 immediately upstream and may be injected into the upstream cavity 17. These gases F2 are relatively hot and therefore have the effect of heating the upstream cavity 17.

[0032] In order to improve the sealing of the seal and increase its service life, the distributor 3 further comprises a deflector 19 configured to guide an air flow towards the upstream cavity 17. For this purpose, the deflector 19 can in particular be mounted on one of the flange 6 and the ring 12 so as to extend substantially radially in the upstream cavity 17. Furthermore, at least one through-orifice 20 is formed in the sealing ring 12 in order to put the part of the upstream cavity 17 located between the deflector 19 and the external face 15b of the ring 12 into fluid communication with the internal face 15a of the sealing ring 12.

[0033] The deflector 19 and the through-orifice(s) 20 thus make it possible to force the cooling fluid F1 (gas) coming from the cells 11 of the disk 8 of the rotor 7 immediately upstream of the distributor 3 to mix with the hot gases F3, F2 coming from the flow stream and the rim 9 of the disk 8, in order to reduce the temperature gradients between the upstream cavity 17 and the downstream cavity 18. Indeed, the rotation of the rotor 7 of the turbine 2 drives the cooling fluid F1 radially outwards, so that the fluid F1 rises along the deflector 19 into the upstream cavity 17, where it meets the hot gases F2, F3. The mixing of the cooling fluid F1 with the hot gases F2, F3 then makes it possible to cool the upstream cavity 17 (and the upstream flange 16a).If necessary, a portion F1a of the mixture thus obtained can then pass between the plates 16a, 16b and the flange 6 through the passage 16a provided for this purpose, thus cooling the downstream cavity 18, while another portion F1b descends towards the wipers 14 via the through orifice(s) 20 and ensures the sealing of the seal.

[0034] The deflector 19 is substantially radial to the X axis. By "substantially radial" it will be understood here that the deflector 19 extends in a plane which can form an angle of between -20° and +20° with a plane normal to the X axis. In one embodiment, the deflector 19 is included in the plane normal to the X axis in order to effectively guide the cooling fluid towards the upstream cavity 17.

[0035] Preferably, several through orifices 20 are formed in the ring 12 in order to ensure sufficient passage for the gas flow coming from the upstream cavity 17. Alternatively, an oblong orifice 20 may be formed in the deflector 19 and / or the ring 12. Since the seal is calibrating, it is not necessary for the passage section of the orifice(s) 20 to participate in the calibration of the gas flow in the seal.

[0036] In a first embodiment, the deflector 19 is fixed to the ring 12, for example by brazing or by mechanical fixing (bolting, etc.). The deflector 19 then comprises an internal radial end arranged near the sealing ring 20 and an external radial end extending into the upstream cavity 17.

[0037] The deflector 19 may for example be fixed at the upstream edge 15c of the ring 12 and extend radially outwardly into the upstream cavity 17. To facilitate the fixing of the deflector 19 on the ring 12, at least one of the ring 12 and the deflector 19 comprises a bent edge on which the other of the deflector 19 and the ring 12 is fixed. For example, the figures 1 And 2illustrate the case of a ring 12 comprising a bent upstream edge 15c, the deflector 19 then being fixed on the bent part of the upstream edge 15c. Preferably, the bent part of the upstream edge 15c of the ring 12 extends radially inwards (i.e. towards the axis X), preferably up to the outlet of the cell 11 (i.e. the end of the upstream edge 15c is opposite the outlet of the cell 11), in order to form an obstacle to the cold cooling fluid F1 coming from the cell 11 of the disc 8 immediately upstream. This configuration thus makes it possible to force the cooling fluid F1 even more to rise towards the upstream cavity 17 rather than flowing directly towards the seal.

[0038] The deflector 19 comprises a substantially planar metal sheet comprising a radially inner edge 19a and a radially outer edge 19b. The radially inner edge 19a and the radially outer edge 19b are preferably annular. The deflector 19 may be monolithic or comprise a plurality of sectors fixed end to end, where appropriate with overlap.

[0039] In this embodiment, the through-orifice(s) 20 are formed in the axial portion 15a of the ring 12, close to the bend. Preferably, the orifice(s) 20 are offset relative to the abradable element 13: they are therefore formed in the portion of the ring 12 which is devoid of abradable element 13, i.e. close to the bend of the upstream edge 15c. By way of example, the orifices 20 may be formed in the bent portion of the upstream edge 15c and extend radially in the bent portion, so as to open out along the deflector 19 (see figure 2). The cooling fluid F1b thus flows through the orifices 20 along the deflector 19 before reaching the seal.

[0040] When the deflector 19 is bent, it further comprises a monolithic annular sheet with the radially inner edge of the metal sheet. The deflector 19 can then be attached and fixed to the outer face 15b of the ring 12, close to its upstream edge 15c. The orifice(s) 20 are then formed in correspondence in the deflector 19 and in the axial portion 15a of the ring 12, at the level of their overlap zone.

[0041] Alternatively, the deflector 19 is monolithic with the ring 12 and can be obtained by additive manufacturing. The orifices 20 are then formed near the junction between the deflector 19 and the axial portion 15a of the ring 12. The deflector 19 can simply form an elbow with the axial portion 15a of the ring 12, or alternatively comprise a radially external portion, which extends from the upstream edge 15c of the ring 12 in the direction of the upstream cavity 17, and a radially internal portion, which extends from the upstream edge 15c of the ring 12 in the direction of the axis X in order to form an obstacle to the passage of cold fluid F1 coming from the cell 11.

[0042] In a second embodiment (not illustrated in the figures), the deflector 19 is fixed on the radial part 16 of the ring 12 or on the flange 6. The deflector 19 then comprises perforations to allow the circulation of the fluid F1 towards the orifices 20 of the ring 12 and, where appropriate (depending on the position relative to the flanges 16a, 16b) towards the gas passage 16c at the level of the flanges 16a, 16b. Furthermore, the deflector 19 comprises an internal radial end extending into the upstream cavity 17 and an external radial end arranged close to the radial part 16 of the sealing ring 20.

[0043] The deflector 19 may comprise a gutter-shaped metal sheet comprising a first flat sheet configured to be fixed to the flange 6 or the radial portion 16 of the ring 12, a second flat sheet extending substantially radially in the upstream cavity 17 and a central sheet connecting the first and second sheets.

[0044] Alternatively, the flange 6 or the radial portion 16 of the ring 12 may comprise a bent sheet metal, which may be brazed onto the radial portion or the flange 6. The deflector 19 may then comprise a bent sheet metal, fixed (for example by brazing) onto the bent sheet metal of the flange 6 or of the radial portion.

[0045] According to yet another variant, the deflector 19 may comprise a radially inwardly bent sheet metal which is monolithic with the flange 6 or the radial portion 16 of the ring 12.

[0046] There figure 4illustrates the circulation of different air flows F1, F2, F3 in a conventional distributor. The hot gases F3 coming from the flow stream leak into the area located between the shell 4 of the distributor 3 and the disc 8 of the rotor 7 immediately upstream. In parallel, a cooling air flow F1 coming from the cell 11 of this disc 8 is injected between the abradable element 13 and the wipers 14 to cool the seal. Finally, a leakage flow F2, hot, near the rim 9 of the discs 8 can be injected into the upstream cavity 17. It is clear from this figure that the cooling fluid F1 does not rise towards the upstream cavity 17, which is therefore very hot, and only cools the seal. This also results in a substantial temperature difference between the upstream cavity 17 and the downstream cavity 18, as well as between the upstream flange 16a and the downstream flange 16b of the ring 12.

[0047] For comparison, the circulation of air flows F1, F2 and F3 is illustrated in the figure 1 , which represents a distributor 3 according to an embodiment of the invention. The hot gases F3 coming from the flow stream are mixed in the upstream cavity 17 with the cooling fluid F1 rising along the deflector 19 and with the hot leakage flow F2 from the rims 9 of the discs 8. The total temperature of the upstream cavity 17 is therefore significantly lower than on the figure 4The temperature differences between the upstream cavity 17 and the downstream cavity 18 as well as between the upstream flange 16a and the downstream flange 16b of the ring 12 are furthermore lower, the gases F1a circulating between the flanges 16a, 16b and the flange 6 also having a lower temperature thanks to its mixture with the fluid F1 coming from the cells 11. Finally, a part F1b of the cold fluid is returned to the seal via the orifices 20 in order to ensure the cooling of the seal.

[0048] Since the upstream cavity 17 is constantly supplied with a high cooling flow, the ring 12 undergoes less significant temperature variations during the lifetime of the turbomachine 1 thanks to the mixing of the gases F1, F2, F3 in the upstream cavity 17. The ring 12 is therefore less subject to thermal expansion.

[0049] The temperature of the upstream 17 and downstream 18 cavities being more homogeneous, the differential thermal expansions between the two flanges 16a, 16b are reduced (or even eliminated). The risks of blocking of the ring 12 (and in particular of its radial movements relative to the flange 6) are therefore eliminated.

[0050] The deflector 19 is preferably made of metal and may be made of the same material as the flange 6 or the ring 12. For example, the deflector 19 may comprise an aluminum alloy, steel, etc.

[0051] The invention can be applied to any axial turbine 2 composed of a succession of moving stages (rotor 7) and static stages (distributors 3), and in particular in the context of turbomachines 1 (and derivatives) and gas turbines. The ring 12 of the turbine 2 can be free, that is to say have radial clearance with the flange 6, or alternatively be fixed relative to the flange 6. The invention finds particular application in the case of turbines 2 having a significant leakage flow rate from the flow stream.

Claims

1. A turbine (2) nozzle guide vanes (3) having an axis of revolution (X) and comprising: - a flange (6) extending radially relative to the axis (X); - a ring seal (12) mounted on the flange (6) and having an inner face (15a) configured to bear an abradable element (13) ; - a ventilation cavity (17) radially delimited on the inside by an outer face (15b) of the ring seal (12) and downstream by an upper face (6a) of the flange (6) ; the nozzle guide vanes (3) being characterized in that it also comprises: - a deflector configured to guide an airflow toward the ventilation cavity (17), the deflector (19) being secured onto a bent upstream edge (15c) of the ring seal (12) which extends radially inwardly; and - at least one through-opening (20) formed in the ring seal (12) and configured to place the ventilation cavity (17) in fluid communication with the inner face (15a) of the ring seal (12).

2. The nozzle (3) according to claim 1, wherein the deflector (19) is mounted on one from among the flange (6) and the ring seal (12) so as to substantially extend radially within the ventilation cavity (17).

3. The nozzle (3) according to one of claims 1 or 2, wherein the upstream edge (15c) extends up to a slot (11) which is formed in the rim (9) of a disc (8) of a rotor of the turbine (2) adjacent to the nozzle.

4. The nozzle (3) according to one of claims 1 to 3, wherein the at least one opening (20) is configured to allow the passing of an airflow from the ventilation cavity (17) toward the inner face (15a) of the ring seal (12).

5. The nozzle (3) according to one of claims 1 to 4, wherein the nozzle (3) comprises a bent metal sheet secured on an upstream edge (15c) of the ring seal (12), the at least one opening (20) passing through the deflector (19).

6. The nozzle (3) according to one of claims 1 to 5, wherein the deflector (19) comprises a substantially planar or frustoconical metal sheet.

7. The nozzle (3) according to one of claims 1 to 6, wherein the deflector (19) extends radially relative to the axis (X).

8. The nozzle (3) according to one of claims 1 to 7, wherein the deflector (19) is brazed onto one from among the flange (6) and the ring seal (12), or it is integral with the ring seal (12).

9. The nozzle (3) according to one of claims 1 to 8, wherein the ring seal (12) is mounted to be radially mobile relative to the flange (6).

10. A turbine (2) comprising a nozzle (3) according to one of claims 1 to 9.

11. A turbine engine (1) comprising a turbine (2) according to claim 10 and an additional turbine, a rotating speed of the additional turbine being greater than a rotating speed of the turbine (2).

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