High-pressure gas turbine for a turbomachine and turbomachine

Abstract

The invention relates to a high-pressure gas turbine for a turbine engine (10), the turbine comprising a nozzle (30), an annular row of moving blades (40) mounted downstream of the nozzle (30), a first recirculation cavity (60), a second recirculation cavity (64) and a purge cavity (62), an upstream seal part (50) mounted on the nozzle (30) and a downstream seal part (50) mounted on the annular row of moving blades (40).

Description

Technical field

[0001] The present invention relates to a high-pressure gas turbine for a turbomachine. It also relates to a turbomachine comprising such a gas turbine. Prior art

[0002] Classically, as represented in the Figure 1, a turbomachine 10 of the double-flow turbojet type comprises, from upstream to downstream in the direction of circulation of the gases inside the turbomachine 10, a fan 14, a low-pressure compressor 16, a high-pressure compressor 18, a combustion chamber 20, a high-pressure turbine 22, a low-pressure turbine 24 and an exhaust nozzle 26. The low-pressure compressor 16, the high-pressure compressor 18, the combustion chamber 20, the high-pressure turbine 22, the low-pressure turbine 24 and the exhaust nozzle 26 are arranged radially inside a casing 12 which delimits, radially outwards, an annular vein 11 of the turbomachine 10 in which the gases flow from upstream to downstream.

[0003] The high-pressure compressor 18 and the low-pressure compressor 16 are respectively connected to a high-pressure turbine 22 and a low-pressure turbine 24 by a respective shaft 15, 17 extending along the longitudinal axis X of rotation of the shafts of the turbomachine 10. In the following, the orientation qualifiers, such as “longitudinal”, “radial” and “circumferential” are defined with reference to the longitudinal axis. Furthermore, the terms upstream and downstream are defined with respect to the direction of circulation of the gases within the turbomachine.

[0004] The high-pressure turbine 22 comprises a plurality of stages, one of which is partially shown in FIG. Figure 2 , each comprising a distributor 30 and a mobile wheel 40 mounted downstream of the distributor 30.

[0005] The distributor 30 comprises an internal annular platform 34 and an annular row of fixed blades 32. Each fixed blade 32 extends radially in the annular vein 11 and is connected, radially inside, to the internal annular platform 34. The distributor 30 generally comprises an annular radial flange 36 for attachment to the casing 5.

[0006] The moving wheel 40 comprises an annular row of moving blades 42 carried by a disc 41 comprising a plurality of cells on its external periphery, each receiving a root 46 of a blade 42. Each moving blade 42 further comprises a sector of an internal annular platform 44 of the moving wheel 40 from which a blade 42' extends radially outwards through the annular vein 11. The internal annular platform 44 thus comprises a plurality of sectors arranged circumferentially end to end around the longitudinal axis X.

[0007] The internal annular platform 34 of the distributor 30 and the internal annular platform 44 of the moving wheel 40 each delimit, radially inwards, the annular vein 11.

[0008] In operation, the gases flowing in the annular vein 11 are introduced into a space formed longitudinally between the internal annular platform 34 of the distributor 30 and the internal annular platform 44 of the moving wheel 40, which reduces the performance of the turbomachine 10. To limit this phenomenon, it is known to arrange, radially inside the internal annular platform 34 of the distributor 30, an upstream annular spoiler 47 of the internal annular platform 44 and a downstream annular spoiler 54 of an annular part 50 for sealing the casing 5. Thus, a baffle is formed in the longitudinal space between the internal annular platform 34 of the distributor 30 and the internal annular platform 44 of the moving wheel 44, limiting the leakage, radially inwards, of the gases flowing in the annular vein 11.

[0009] Furthermore, a purge air flow, taken from the low-pressure compressor 16 and / or the high-pressure compressor 18, is directed through an annular purge cavity 62 towards the space formed longitudinally between the internal annular platform 34 of the distributor 30 and the internal annular platform 44 of the mobile wheel 4. This purge air flow thus makes it possible to redirect the gases that have entered the purge cavity 62 towards the annular vein 11.

[0010] However, this solution is not entirely satisfactory in that the air sampling taken at the low-pressure compressor 16 and / or the high-pressure compressor 18 reduces the efficiency of the turbomachine 10. Furthermore, the reintroduction, into the annular vein 11, of the purge air and the gases having entered the purge cavity 62 disturbs the flow in the annular vein 11, which also reduces the performance of the turbomachine 10. US 2015 / 354391 discloses the state of the prior art, which does not comprise a downstream sealing part applied against an upstream face of the disc of the annular row of moving blades, but on the contrary a downstream sealing portion made from the same material and constituting the upstream face of the disc of the annular row of moving blades.

[0011] US 9,605,552 B2 generally discloses a downstream sealing part applied against an upstream face of a disc of an annular row of moving blades. Summary

[0012] The present invention improves the situation.

[0013] The present invention consists of a high-pressure gas turbine for a turbomachine extending about a longitudinal axis, the turbine comprising: a distributor comprising an internal annular platform and an annular row of fixed blades, each fixed blade being connected, radially inwards, to the internal annular platform, an annular row of moving blades mounted downstream of the distributor, comprising a disc from which blades extend radially outwards, an upstream sealing part applied against a downstream face of the distributor and a downstream sealing part an upstream face of the disc of the annular row of moving blades, the downstream sealing part comprising an upstream spoiler arranged, at least in part, radially inside the internal annular platform of the distributor, the upstream sealing part comprising a first downstream spoiler, arranged, in whole or in part, radially inside the upstream spoiler of the upstream sealing part, the first downstream spoiler forming a projection radially towards the outside of the sealing part, a radially external end of said first downstream spoiler being arranged radially opposite said upstream spoiler, thus forming a first annular recirculation cavity which is delimited, longitudinally, by the distributor and the first downstream spoiler, the upstream sealing part comprising a second downstream spoiler forming a projection towards the downstream, the second downstream spoiler being arranged radially inside the first downstream spoiler,the downstream sealing part comprising an upstream face extending radially and without a spoiler interposed radially between said first downstream spoiler and second downstream spoiler of the upstream sealing part, thus forming a second annular recirculation cavity which is delimited by said first downstream spoiler and second downstream spoiler of the upstream sealing part and by the upstream face of the downstream sealing part, an annular purge cavity being delimited between the distributor and the annular row of moving blades and located radially inside the second annular recirculation cavity, a purge air flow or a gas flow being able to flow between an annular vein located radially outside the internal platform of the distributor and the first annular circulation cavity, through a clearance between the internal platform and the upstream spoiler, between the first recirculation cavity and the second recirculation cavity,through a clearance between the first downstream spoiler and the upstream spoiler, and between the second recirculation cavity and the purge cavity, through a clearance between the second downstream spoiler and the downstream sealing part.

[0014] The arrangement of the first downstream spoiler delimiting the first annular recirculation cavity allows the formation of a swirl, or vortex, of the gases from the annular vein which are introduced into the first annular recirculation cavity, these gases mixing with a flow of purge air coming from the second annular recirculation cavity and from the annular purge cavity. Such a swirl makes it possible, on the one hand, to limit, or even prevent, the gases from the annular vein from flowing further radially inwards, and on the other hand, to redirect these gases towards the annular vein. In other words, the swirl obstructs a flow, radially inwards, of the gases coming from the annular vein. The gases coming from the annular vein entering the first annular recirculation cavity are thus advantageously mainly contained in the first annular recirculation cavity.

[0015] The second annular recirculation cavity also allows the formation of a swirl, or vortex, of the gases from the first annular recirculation cavity which are introduced into the secondary annular recirculation cavity, these gases mixing with a flow of purge air coming from the annular purge cavity. As previously, such a swirl makes it possible to limit, or even prevent, the gases from flowing further radially inwards, and on the other hand, to redirect these gases towards the first annular recirculation cavity. In other words, the swirl here prevents a flow, radially inwards, of the gases coming from the first annular recirculation cavity. The gases coming from the first annular recirculation cavity introduced into the second annular recirculation cavity are thus advantageously mainly contained in the secondary annular recirculation cavity.

[0016] This reduces the amount of gas from the annular vein entering the annular purge cavity.

[0017] Furthermore, the bleed air flow rate required to redirect the gases that have entered the first and second annular recirculation cavities to the annular flow path is reduced. Thus, the elements of the annular row of moving blades are better protected. Also, the amount of bleed air taken from the high-pressure compressor and / or the low-pressure compressor is reduced, which improves the efficiency of the turbomachine.

[0018] The feature that the first downstream spoiler protrudes radially outwardly from the sealing part is, in other words, equivalent to the first downstream spoiler extending radially outwardly from an annular portion of the sealing part. The first downstream spoiler may extend from a radially outer end of the annular portion of the sealing part.

[0019] Furthermore, the feature that the second downstream spoiler forms a projection downstream of the sealing part is equivalent, in other words, to the second downstream spoiler extending longitudinally downstream from an annular portion of the sealing part.

[0020] The first downstream spoiler may extend radially outward from a radially outer end of an annular portion of the upstream sealing part, said first annular recirculation cavity being delimited, radially inward, by a radially outer face of the annular portion of the upstream sealing part, the radially outer annular face of said annular portion having, in whole or in part, a concave shape.

[0021] The concave shape further promotes the formation of a vortex or whirlpool within the first recirculation cavity.

[0022] The first downstream spoiler may extend radially outward from a radially outer end of an annular portion of the upstream sealing part, the first downstream spoiler comprising a downstream-flaring frustoconical wall extending from the radially outer and downstream end of the annular portion of the upstream sealing part and a radial wall extending radially outward from a downstream end of said frustoconical wall.

[0023] The second downstream spoiler can be cylindrical, that is, can extend longitudinally downstream.

[0024] The angle between the truncated wall of the first downstream spoiler and the second downstream spoiler is between 30 and 45°, preferably between 35 and 40°.

[0025] Such an angle promotes the formation of vortices or whirlpools in each of the first and second recirculation cavities.

[0026] The second downstream spoiler may be arranged axially opposite a recess or a step provided in the downstream sealing part in order to maintain a minimum axial clearance between the second downstream spoiler and the downstream sealing part.

[0027] Such a recess or detachment helps to promote the formation of a vortex or whirlpool in the second recirculation cavity, and prevents the introduction of hot gases into the purge cavity.

[0028] The upstream spoiler may have a radially external face which is of truncated cone shape with a section decreasing towards the upstream extending over at least a first longitudinal portion.

[0029] Such a shape makes it easier to evacuate purge air and gases from the first recirculation cavity to the annular vein. Furthermore, such a feature makes it possible to adapt the direction in which the gases mixed in the annular vein are reintroduced into the annular vein to minimize disturbances to the gases flowing in the annular vein.

[0030] The distributor may further comprise a radial annular flange extending radially inwardly from the inner annular platform, the upstream sealing part being attached and fixed to the radial annular flange.

[0031] The second downstream spoiler may have a radially outwardly projecting portion at its downstream end.

[0032] According to another aspect of the invention, a turbomachine is described comprising a high-pressure gas turbine of the aforementioned type. Brief description of the drawings

[0033] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: [ Fig. 1 ], already described previously, is a partial schematic sectional view of a turbomachine of the prior art; [ Fig. 2 ], already described previously, is a partial schematic sectional view of a high-pressure turbine of the turbomachine of the Figure 1 ; [ Fig. 3 ] is a partial schematic perspective and sectional view of a high-pressure turbine according to an embodiment of the present document; [ Fig. 4 ] is a partial schematic sectional view of the turbine of the Figure 3 ; [ Fig. 5 ] is a detail view of the Figure 4 ; [ Fig. 6 ] is a view corresponding to the Figure 5 , illustrating an alternative embodiment. Description of the embodiments

[0034] Reference is now made to the figures 3 to 5which represent, according to a first embodiment, partially a high-pressure turbine of a turbomachine with longitudinal axis X. The high-pressure turbine comprises a plurality of stages each comprising a distributor 30 and a mobile wheel 40 mounted downstream of the distributor 30.

[0035] The distributor 30 comprises an annular row of fixed blades 32. Each fixed blade 32 is connected, radially inward, to an inner annular platform 34 of the distributor 30. Each fixed blade 32 extends radially outward from the inner annular platform 34. Each fixed blade 32 is connected, radially outward, to an outer platform 34' connected to an outer casing of the high-pressure turbine. A radially outer annular face of the inner annular platform 34 and a radially inner annular face of the outer platform 34' delimit, radially, respectively inwardly and outwardly, an annular vein 11 of the turbomachine 10 at the distributor 30 of the high-pressure turbine. Thus, each fixed blade 32 extends radially inside the annular vein 11.

[0036] The distributor 30 further comprises a radial annular flange 36 extending radially inward from the internal annular platform 34. The distributor 30 can be connected to an internal turbomachine casing via the radial annular flange 36.

[0037] The movable wheel 40 comprises an annular row of movable blades 42 carried by a disc 41. The movable wheel 40 comprises an internal annular platform 44. Each movable blade 42 of the movable wheel 40 comprises a sector of the internal annular platform 44, the sectors being arranged circumferentially end to end around the longitudinal axis X. A radially external annular face 44a of the internal annular platform 44 delimits, radially inwards, the annular vein 11 at the movable wheel 40 of the turbine. Each movable blade 42 comprises a blade 42' extending, radially outwards, into the annular vein 11 from the respective sector of the internal annular platform 44.

[0038] The movable wheel 40 also comprises a downstream sealing part 43 attached and fixed to an upstream radial surface of the disc 41 and of the zone comprising the platform 44. The downstream sealing part 43 comprises an upstream annular spoiler 47 which is annular and which extends at the level of the radially external end of the downstream sealing part 43. The upstream annular spoiler 47 is arranged, here in part, radially inside the internal annular platform 34 of the distributor 30. In other words, the upstream annular spoiler 47 is arranged radially inside the internal annular platform 34 of the distributor 30 and, in part, radially opposite the internal annular platform 34 of the distributor 30. The upstream end of the upstream spoiler 47 is located longitudinally further upstream than the downstream end of the internal platform 34. The downstream sealing part 43 may be an integral part of the disk 41 and / or the platform 44.

[0039] The high-pressure turbine further comprises an upstream sealing part 50, which is here annular, applied against a downstream face of the distributor 30. The upstream sealing part 50 is here attached and fixed to the radial annular flange 36. To do this, the upstream sealing part 50 comprises an annular part 52 applied against a downstream face of the radial annular flange 36 of the distributor 30. The annular part 52 of the upstream sealing part 50 can be fixed, for example by bolting, to the radial annular flange 36 of the distributor 30. The upstream sealing part can be an integral part of the casing of the high-pressure turbine.

[0040] The upstream sealing part 50 comprises a first downstream spoiler 54 which is annular. The first downstream annular spoiler 54 is arranged, here in part, radially inside the upstream annular spoiler 47 of the downstream sealing part 43. In other words, the first downstream annular spoiler 54 is arranged radially inside the upstream annular spoiler 47 and, in part, radially opposite the upstream annular spoiler 47. The first downstream annular spoiler 54 extends radially outward from a radially outer end of the annular portion 52 of the annular sealing part 50. Remarkably, a radially outer end 55 of the first downstream annular spoiler 54 is arranged radially opposite the upstream annular spoiler 47, thus forming a first annular recirculation cavity 60 which is delimited, longitudinally, by the distributor 30 and the first downstream spoiler 54.The first annular recirculation cavity 60 is here delimited, radially outwards, by a radially internal face 34a of the internal annular platform 34 of the distributor 30. The first annular recirculation cavity 60 is delimited, radially inwards, by a radially external annular face 52a of the annular part 52 of the upstream annular sealing part 50. The first annular recirculation cavity 60 here forms a free space. In other words, the first annular recirculation cavity 60 is here devoid of any solid element.

[0041] Remarkably, a free space is formed, longitudinally, between the internal annular platform 34 of the distributor 30 and the internal annular platform 44 of the movable wheel 40. The internal annular platform 34 of the distributor 30 and the upstream annular spoiler 47 of the movable wheel 40 together define a clearance or flow conduit between the annular vein 11 and the first annular recirculation cavity 60.

[0042] Such an arrangement of the first downstream annular spoiler 54 delimiting the first annular recirculation cavity 60 allows the formation of a swirl, or vortex (illustrated by arrows at the Figure 4), gases flowing in the annular vein 11 which are introduced into the first annular recirculation cavity 60, these gases mixing with a flow of purge air coming from an annular purge cavity 62 and from a second annular recirculation cavity 64 located radially inwards between the distributor 30 and the movable wheel 40. Such a vortex makes it possible, on the one hand, to limit, or even prevent, the gases of the vein 11 from flowing further radially inwards, and on the other hand, to redirect these gases towards the annular vein 11. In other words, the vortex prevents a flow, radially inwards, of the gases coming from the annular vein 11. The gases coming from the annular vein 11 entering the first recirculation cavity 60 are thus advantageously contained in this cavity 60.Thus, the quantity of gas from the annular vein 11 which enters the second recirculation cavity 64 and the annular purge cavity 62 is reduced.

[0043] Furthermore, the purge air flow rate required to redirect the gases that have entered the first annular recirculation cavity 60 to the annular flow path 11 is reduced. Thus, the mobile wheel elements 40 are better protected. Also, the quantity of purge air taken from the high-pressure compressor and / or the low-pressure compressor is reduced, which makes it possible to improve the efficiency of the turbomachine.

[0044] In reference to the Figure 5 which is a larger scale view of the Figure 4, it is distinguished that the first downstream annular spoiler 54 comprises a frustoconical wall 54a flared downstream and extending from the radially external and downstream end of the annular portion 52 of the annular sealing part 50. The thickness of the frustoconical wall 54a decreases slightly downstream. The first downstream annular spoiler 54 also comprises a radial annular wall 54b extending radially outward from a downstream end of the frustoconical wall 54a. A radial clearance is formed between the radially external end of the first downstream spoiler 54 and the upstream spoiler 47, allowing the passage of a purge air flow coming from the second recirculation cavity 64 and the purge cavity 62. The annular portion 52 of the annular sealing part 50 has a radially external annular face 52a having a concave shape.

[0045] The first downstream annular spoiler 54 may also have a plurality of holes (not shown) which may be regularly distributed circumferentially around the longitudinal axis X. The plurality of holes may extend through the frustoconical wall 54a of the first downstream annular spoiler 54. This allows a purge air flow to pass through the holes 56 towards the first annular recirculation cavity 60, in particular at the level where the pressure of the gases in the first annular recirculation cavity 60 is the highest. This further limits the introduction of gases coming from the annular vein 11 into the second recirculation cavity 64 and into the annular purge cavity 62.

[0046] Furthermore, as visible in the figures 3 And 4, the first upstream annular spoiler 47 has a radially external annular face 47a which is of truncated cone shape with a section decreasing towards the upstream and which extends over a first longitudinal portion of the first upstream annular spoiler 47. The first portion of the upstream annular spoiler 47 is, here in part, radially opposite the internal annular platform 34 of the distributor 30. The radially external annular face 47a of the first portion of the upstream annular spoiler 47 is here connected to the radially external annular face 44a of the internal annular platform 44 of the moving wheel 40, in particular by a rounding.

[0047] In operation, the gases from the annular flow path 11 introduced into the first annular recirculation cavity 60 via the conduit or clearance formed between said upstream annular spoiler 47 and the internal annular platform 34 of the distributor 30 are mixed with the purge air flow to be redirected to the annular flow path 11. Such a radially external annular face 47a of the upstream annular spoiler 47 makes it possible to adapt the direction in which the gases mixed in the annular flow path 11 are reintroduced into the annular flow path 11 to minimize disturbances on the gases flowing in the annular flow path 11. In particular, the conicity of the radially external annular face 47a of the upstream annular spoiler 47 may be chosen to minimize disturbances on the gases flowing in the annular flow path 11.

[0048] The radially internal annular face 34a of the internal annular platform 34 of the distributor 30 has, here in part, a concave shape which is arranged radially opposite the upstream annular spoiler 47. Such a concave shape of the radially internal annular face 34a of the internal annular platform 34 of the distributor 30 makes it possible to promote the appearance of a vortex at the interface between the gases coming from the annular vein 11 and the purge air.

[0049] Furthermore, the upstream sealing part 50 comprises a second downstream annular spoiler 58 arranged radially inside the first downstream annular spoiler 54. The second downstream annular spoiler 58 extends longitudinally downstream from the annular portion 52 of the annular sealing part 50. The second downstream spoiler 58 has a cylindrical shape and forms an angle of between 30 and 45°, preferably between 35 and 40°, with the frustoconical wall 54a of the first downstream spoiler 54. The second downstream spoiler 58 is located axially opposite an annular recess 43a formed in the downstream sealing part 43. An axial clearance is formed between the downstream end of the second downstream spoiler 58 and the bottom wall of the recess 43a, so as to allow the passage of a purge air flow coming from the purge cavity 62.

[0050] The second recirculation cavity 64 is delimited by the first downstream spoiler 54, the second downstream spoiler 58 and the upstream surface of the second sealing part 43.

[0051] In operation, a small quantity of gases from the first annular recirculation cavity 60 can flow into the second recirculation cavity 64 through the clearance formed between the upstream spoiler 47 and the first downstream spoiler 54. These gases are then mixed with the purge air flow from the purge cavity 62, entering the second recirculation cavity 64 through the clearance formed between the second downstream spoiler 58 and the downstream sealing part 43. Once mixed with the air, these gases are redirected towards the first recirculation cavity 60 then towards the annular vein 11. The shape of the second cavity 64 makes it possible to generate vortices or whirlpools, illustrated by arrows at the Figure 4, making it possible to facilitate such mixing and such evacuation. This limits, or even prevents, a flow of gases towards the purge cavity 62.

[0052] There Figure 6 illustrates an alternative embodiment in which a portion of the second downstream spoiler 58, for example the downstream end of the second downstream spoiler, comprises a projecting portion 58a radially outwardly, for example an oblique portion radially outwardly and longitudinally downstream. Such a projecting portion 58a makes it possible to further improve the evacuation efficiency of the vortex created at the level of the second recirculation cavity 64.

[0053] The invention is not limited to the examples described above and is susceptible of numerous variations, but is defined by the statement of the claims. In particular, the embodiments are capable of being combined, within the framework of the statement of the claims.

[0054] According to a variant not forming part of the claimed invention and not shown, the annular sealing part 50 may be made in one piece with the radial annular flange 36 of the distributor 30.

[0055] According to a variant not shown, the annular sealing part 50 may comprise a plurality of sectors arranged circumferentially end to end around the longitudinal axis X.

Claims

1. High-pressure gas turbine for a turbomachine (10) extending around a longitudinal axis (X), the turbine comprising: - a nozzle guide vane assembly (30) comprising an internal annular platform (34) and an annular array of fixed vanes (32), each fixed vane (32) being connected, radially inwards, to the internal annular platform (34), - an annular array of movable blades (40) mounted downstream of the nozzle guide vane assembly (30), comprising a disc (41) from which blades (42) extend radially outwards, - an upstream sealing element (50) applied against a downstream face of the nozzle guide vane assembly (30), and a downstream sealing element (43) applied against an upstream face of the disc (41) of the annular array of movable blades (40), the downstream sealing element (43) comprising an upstream deflector (47) arranged, at least in part, radially internally to the internal annular platform (34) of the nozzle guide vane assembly (30), the upstream sealing element (50) comprising a first downstream deflector (54) arranged, in whole or in part, radially internally to the upstream deflector (47) of the upstream sealing element (50) (50), the first downstream deflector (54) forming a radially outward projection from the sealing element (50), a radially external end (55) of said first downstream deflector (54) being arranged radially facing said upstream deflector (47), thus forming a first annular recirculation cavity (60) which is delimited, longitudinally, by the nozzle guide vane assembly (30) and the first downstream deflector (54), the upstream sealing element (50) comprising a second downstream deflector (58) forming a projection in the downstream direction, the second downstream deflector (58) being arranged radially internally to the first downstream deflector (54), the downstream sealing element (43) comprising an upstream face extending radially and without any deflector interposed radially between said first downstream deflector (54) and said second downstream deflector (58) of the upstream sealing element (50), thus forming a second annular recirculation cavity (60) which is delimited by said first downstream deflector (54) and said second downstream deflector (58) of the upstream sealing element (50) and by the upstream face of the downstream sealing element (43), an annular bleed cavity (62) being delimited between the nozzle guide vane assembly (30) and the annular array of movable blades (40) and located radially internally to the second annular recirculation cavity (64), a stream of bleed air or a stream of gas being able to flow: between an annular path (11) located radially externally to the internal platform (34) of the nozzle guide vane assembly (30) and the first annular circulation cavity (60), through a clearance between the internal platform (34) and the upstream deflector (47); between the first recirculation cavity (60) and the second recirculation cavity (64), through a clearance between the first downstream deflector (54) and the upstream deflector (47); and between the second recirculation cavity (64) and the bleed cavity (62), through a clearance between the second downstream deflector (58) and the downstream sealing element (43).

2. Turbine according to claim 1, wherein the first downstream deflector (54) extends radially outwards from a radially external end of an annular portion (52) of the sealing element (50), said first annular recirculation cavity (60) being delimited, radially inwards, by a radially external face (52a) of the annular portion (52) of the sealing element (50), the radially external annular face (52a) of said annular portion (52) having, in whole or in part, a concave shape.

3. Turbine according to any one of the preceding claims, wherein the first downstream deflector (54) extends radially outwards from a radially external end of an annular portion (52) of the downstream sealing element (43) (50), the first downstream deflector (54) comprising a frustoconical wall (54a) which widens in the downstream direction, extending from the radially external and downstream end of the annular portion (52) of the upstream sealing element (50), and a radial wall (54b) extending radially outwards from a downstream end of said frustoconical wall (54a).

4. Turbine according to any one of the preceding claims, wherein the second downstream deflector (58) is cylindrical.

5. Turbine according to claims 3 and 4, wherein the angle between the frustoconical wall (54a) of the first downstream deflector (54) and the second downstream deflector (58) is between 30 and 45°, preferably between 35 and 40°.

6. Turbine according to any one of the preceding claims, wherein the second downstream deflector (58) is arranged axially opposite a recess (43a) or a niche provided in the downstream sealing element (43).

7. Turbine according to any one of the preceding claims, wherein the upstream deflector (47) has a radially external face (47a) which is of frustoconical shape with a decreasing cross-section in the upstream direction, extending over at least a first longitudinal portion.

8. Turbine according to any one of the preceding claims, wherein the nozzle guide vane assembly (30) further comprises a radial annular flange (36) extending radially inwards from the internal annular platform (34), the upstream sealing element(50) being attached and fixed to the radial annular flange (36).

9. Turbine according to any one of the preceding claims, wherein the second downstream deflector (58) includes a portion (58a) which projects radially outwards at its downstream end.

10. Turbomachine comprising a high-pressure gas turbine according to any one of the preceding claims.

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