WO2025037058A1 - Seal for a turbine engine - Google Patents

Abstract

The present application relates to an annular seal comprising a plurality of seal sectors distributed circumferentially about a longitudinal axis (A), each seal sector comprising an inner ring sector (30) that is connected to an outer ring sector by a return member, the inner ring sector (30) comprising: a first circumferential end (37) and a second circumferential end; a cylindrical outer upstream surface (32.1) extending circumferentially from the first circumferential end (37) to the second circumferential end; an outer downstream surface (46.1) extending circumferentially at a distance from the first and second ends (37), the outer downstream surface (46.1) having a first cylindrical surface (46.11) located in a first radial position as well as a second cylindrical surface (46.12) located in a second radial position that differs from the first radial position.

Description

Description

Title: Gasket for turbomachine

Technical field

[0001] The present disclosure relates to the design of a seal for a turbomachine as well as a turbomachine comprising such a seal.

Previous technique

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft but also to those in circulation requiring the implementation of technological solutions in order to make them compliant with the regulations in force. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0004] In this context, engine efficiency is constantly being improved, which sometimes has an impact on the temperature of the gases or structural elements downstream of the combustion chamber. Controlling temperatures at the turbine level is essential for reasons of mechanical strength and control of expansion deformations.

[0005] Patent document FR 3 080 406 A1 describes a turbine distributor in which the blades are hollow and are adapted to receive a flow of air cooling the blades and taken from the compressor.

[0006] The cooling air for the turbines can be taken downstream of the compressor and radially below the combustion chambers. This air flow passes through three seals: a seal downstream of the high-pressure compressor, called “CDP” for “compressor discharge pressure” in English; an internal seal, called “FIS” for “forward inner seal” in English; and an external seal, called “FOS” for “forward outer seal” in English. These seals are generally labyrinth seals. Labyrinth seals are formed of lips arranged on the rotor which cooperate with an abradable of the stator. The abradable can have a honeycomb-type alveolar structure.

[0007] The disadvantage of this type of seal lies in the fact that the friction of the licks on the abradable tends to deteriorate the abradable and consequently to increase the clearance between rotor and stator. This induces an increase in the air flow through the seals. Depending on the seal in question (CDPD, FIS, FOS), this means an increase or decrease in the air flow supplied to the turbines and therefore a deviation from a target value of air flow. Thus, the increase in the clearance between these seals and the rotors can have two major consequences: a reduction in the efficiency of the turbomachine, and insufficient cooling of the turbines.

[0008] Therefore, there is a need to ensure consistency of flow rates through the seals over the entire life of the seals.

Summary

[0009] The present invention aims to propose a turbomachine seal which makes it possible to control the flow of cooling air supplied to the turbines, regardless of its service life.

[0010] For this purpose, the present document relates to an annular sealing gasket comprising a plurality of gasket sectors distributed circumferentially around a longitudinal axis, each gasket sector comprising an inner ring sector connected to an outer ring sector by a return member, the inner ring sector comprising: a first circumferential end and a second circumferential end; an outer, cylindrical upstream surface extending circumferentially from the first circumferential end to the second circumferential end; an outer downstream surface extending circumferentially at a distance from the first and second ends, the outer downstream surface having a first cylindrical surface arranged at a first radial position and a second cylindrical surface arranged at a second radial position distinct from the first radial position; and an outer central lip arranged between the outer upstream surface and the outer downstream surface, the outer central lip extending circumferentially from the first circumferential end to the second circumferential end.

[0011] Such a seal architecture differs from a labyrinth seal. The external upstream and external downstream surfaces form air bearing surfaces on the seal. The lift of the internal sector on these surfaces ensures that a predefined clearance is maintained with the internal rotor. The design of the internal ring sector thus allows hydrostatic self-regulation of the position of the internal ring sector relative to the rotor.

[0012] It is obvious that the sealing in question here is not a strict sealing in the sense that air could not pass through the seal, but a relative sealing, the purpose of the seal being to allow a controlled quantity of air to pass through.

[0013] It is understood that the predefined clearance is a "target" clearance, and that it is possible for the clearance to vary slightly around the predefined clearance value under certain conditions of use of the seal. When the seal is in its equilibrium position, the predefined clearance ensures that the airflow through the seal is the desired airflow. However, if the clearance increases or decreases, the seal will be returned to the predefined clearance in relation to a spring behavior of the internal ring sectors ensured in particular by the return organs and the air flow.

[0014] More specifically, if the clearance between the seal and the rotor becomes smaller than the predefined clearance, the air friction at the interface between the rotor and the inner surface of the seal tends to move the inner ring sector so as to increase the clearance. Conversely, if the clearance between the seal and the rotor becomes larger than the predefined clearance, the return member exerts a force greater than the lift of the inner ring sectors, the inner ring sectors then returning to their equilibrium positions, i.e. to the predefined clearance. The stepped design of the first and second cylindrical surfaces makes it possible to limit the mass of the inner sector while maintaining equilibrium.

[0015] This mechanical-aerodynamic balance which regulates a predefined clearance also makes it possible to avoid any contact between the rotor and the seal, thus overcoming the problem of wear encountered for conventional labyrinth seals. In particular, when cold, the clearance observed may be greater than in known designs.

[0016] The outer central lip forms an obstacle to the flow of air. It can extend radially over a large part of the space between the inner ring sector and the outer ring sector. Alternatively, it can be radially narrower. It can thus form a bearing surface for a secondary sealing member.

[0017] The “circumferential distribution” of the seal sectors is intended to mean that each seal sector defines a portion of the circumference of the seal, and that the set of seal sectors makes it possible to obtain the complete seal. Optionally, the distribution is regular and each seal sector then represents an equal portion of the circumference of the sealing gasket.

[0018] The terms “internal” and “external”, or indifferently “interior” and “exterior”, refer to a radial position relative to the longitudinal central axis of the seal around which the seal sectors are arranged. “Upstream” and “downstream” are to be understood in the main direction of flow of the flow in a turbomachine.

[0019] According to one embodiment, the external upstream surface has an axial length of between 40 and 45% of the total axial length of the internal ring sector and the external downstream surface has an axial length of between 50 and 70% of the total axial length of the internal ring sector.

[0020] Since the pressure is higher upstream of the seal, this length ratio guarantees a balance of the seal and therefore control of the clearance between the seal and the rotor.

[0021] The total axial length of the seal may be greater than or equal to 15 mm. [0022] According to one embodiment, a wall arranged at a circumferential end and a base intended to connect the return member to the internal ring sector circumferentially delimit the external downstream surface.

[0023] It is thus possible to limit edge effects and to properly control the flow of the fluid and therefore to properly control the clearance between the seal and the rotor.

[0024] According to one embodiment, an internal frustoconical surface extends away from the longitudinal axis at a downstream end of the internal ring sector.

[0025] This surface forms a diffuser which makes it possible to reduce the flow passing radially under the internal ring sector. This conical surface may be inclined by less than 15° relative to the longitudinal axis (moving away from the axis downstream) and/or which may extend axially over less than 10% of the total axial length of the seal. These limits make it possible not to deteriorate the bearing capacity of the internal ring sector by the presence of the diffuser.

[0026] According to one embodiment, the inner ring sector comprises an upstream lip projecting upstream and towards the longitudinal axis, and an inner central lip projecting radially towards the longitudinal axis, the upstream lip and the inner central lip each having a respective distal end arranged at a respective radius, the radius of the distal end of the upstream lip being greater than the radius of the distal end of the inner central lip. The radii are measured relative to the central axis of the turbomachine.

[0027] The radial clearance between the upstream lip and the rotor is therefore greater than that between the internal central lip and the rotor, thus ensuring an increase in pressure (air cushion), the air arriving more easily in the space between the rotor, the upstream lip and the internal central lip than it escapes. The difference between the radial positions of the two distal ends can be between 0.2 and 0.6 mm for a seal of length equal to or greater than 15 mm.

[0028] The internal central lip can be said to be “calibrating” in the sense that it can be one of the elements closest to the rotor.

[0029] In other words, the internal lip forms an obstacle to the flow of air which, with the upstream lip, when the clearance is less than the predefined clearance, makes it possible to increase the pressure at the interface between the seal and the rotor, in order to help push the seal radially outwards and assist in restoring the predefined clearance.

[0030] According to one embodiment, a first cavity is formed between the upstream lip and the internal central lip, the axial length of the first cavity being between 40 and 70% of the total axial length of the internal ring sector. Preferably this range is reduced to 50 to 60%.

[0031] This cavity is thus of sufficient size to create an increase in pressure under the internal ring sector without being too large, leaving space for other components of the ring sector (diffuser, internal cylindrical surface in particular). [0032] According to one embodiment, a first thickness is defined by the distance separating the external upstream surface from the first cavity and a second thickness is defined by the distance between the first cylindrical surface and the first cavity, the second thickness preferably being at least 30% less than the first thickness.

[0033] It is thus possible to lighten the internal sector and to design springs more precisely guaranteeing good control of the play during the life of the seal.

[0034] According to one embodiment, the first and second thicknesses are greater than 1 mm.

[0035] Thus, the internal ring sector has sufficient rigidity for the design of the return member to be robust: elements with thicknesses that are too thin could deform during use and could prevent the design of a return member and a ring sector geometry allowing precise control of the clearance during the life of the seal.

[0036] According to one embodiment, the distal end of the upstream lip is chamfered.

[0037] This chamfer allows only a small part of the upstream air flow to be directed under the internal sector. The chamfer may be less than 0.2 mm in size.

[0038] According to one embodiment, the internal ring sector comprises a truncated cone-shaped frontal surface which forms with the upstream lip an angle greater than or equal to 90°.

[0039] The recess thus formed makes it possible to lighten the internal ring sector and to flow back the air arriving from upstream. The recess can be symmetrical in the sense that the upstream lip and the conical front surface are, in a longitudinal section, symmetrical with respect to the horizontal.

[0040] According to one embodiment, the internal ring sector comprises an internal downstream cylindrical surface with an axial length of between 15 and 25% of the total axial length of the internal ring sector.

[0041] This downstream cylindrical surface makes it possible to pressurize the internal cavities of the ring sector and to increase the lift of the internal ring sector, thus regulating the clearance with the rotor.

[0042] According to one embodiment, a second cavity is formed between the internal central lip and the internal downstream cylindrical surface, the axial length of the second cavity being less than 10% of the total length of the internal ring sector.

[0043] The second cavity makes it possible to lighten the ring sector without altering the air flow at the interface between the seal and the rotor.

[0044] According to one embodiment, a second cavity is formed between the inner central lip and the inner downstream cylindrical surface, and the distance separating the first cylindrical surface from the first cavity is equal to the distance separating the first cylindrical surface from the second cavity, and is equal to the distance separating the second cylindrical surface from the inner downstream cylindrical surface. [0045] According to one embodiment, the seal further comprises a secondary sealing member arranged radially between the internal ring sector and the external ring sector and arranged upstream of the return member, the secondary sealing member bearing on the external central lip.

[0046] The secondary sealing member prevents air from axially passing through the seal above the inner ring sector. In other words, such a secondary sealing member ensures that the only path for air to pass through the seal is the (controlled) clearance between the inner surface of the inner ring sector and the outer surface of the rotor opposite the seal.

[0047] The secondary sealing member may for example be chosen from a brush seal, a set of tabs, or a tile. It may be supported upstream of the external central lip or supported downstream of the external central lip.

[0048] In one embodiment, the outer ring sectors form an outer ferrule and the inner ring sectors have ends arranged end-to-end in the circumferential direction.

[0049] In such an embodiment, the circumferential ends of the inner ring sectors may have an angle of inclination relative to the circumferential direction of between 30° and 90°. Alternatively, the angle may be between 0° and 30°.

[0050] An inclination of the ends of the internal ring sectors makes it possible to reduce the clearance existing between two internal ring sectors, thus improving the effectiveness of the seal.

[0051] In one embodiment, the seal comprises between 8 and 20 seal sectors.

[0052] This range of values constitutes a good compromise between too few sectors, synonymous with heavy sectors for the return organs, and too many sectors, synonymous with numerous inter-sector gaps and therefore potential air leaks.

[0053] In one embodiment, the outer ring sectors of a seal may be a single part, for example a ferrule. In other words, there is no physical separation between two circumferentially successive outer ring sectors.

[0054] In one embodiment, such a ferrule may be monolithic, i.e. made in a single piece without connection. In such a case, it will be considered that an angular portion of the ferrule can be considered as an external ring sector.

[0055] The invention also relates to a turbomachine comprising: a high-pressure compressor; a combustion chamber; a high-pressure turbine; a first, a second and a third seal; and a circuit for conveying cooling air to the high-pressure turbine, the air conveying circuit comprising an air inlet downstream of the high-pressure compressor, a duct separated from the inlet by the first seal, a housing separated from the duct by the second seal, an air injector opening into the housing, a purge outlet separated from the housing by the third seal and an air outlet from the housing. directing the air flow towards the high pressure turbine, at least one of the first, second and third seals being in accordance with one of the embodiments set forth above.

[0056] Depending on the position envisaged, the first seal is a seal downstream of the high-pressure compressor (called “CDP” for “compressor discharge pressure” in English), the second seal is a forward inner seal (called “FIS” for “forward inner seal” in English) and the third seal is a forward outer seal (called “FOS” for “forward outer seal” in English).

[0057] It has been found that the seals of the invention allow better control of the clearance during their service life than labyrinth seals, and thus ensure maintenance of the performance of the turbomachine and efficient cooling of the turbines throughout the life of the seal.

Brief description of the drawings

[0058] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the attached drawings, in which:

[0059] [Fig. 1] is a schematic sectional view of a turbomachine;

[0060] [Fig. 2] is a sectional view of a turbine cooling circuit;

[0061] [Fig. 3] is a front view of a seal according to the invention;

[0062] [Fig. 4] is an upstream isometric view of an inner ring sector;

[0063] [Fig. 5] is a downstream isometric view of an internal ring sector;

[0064] [Fig. 6] is a sectional view of an inner ring sector.

Description of the embodiments

[0065] The figures describe different aspects of the invention schematically. The dimensions are not shown to scale: certain dimensions are enlarged to facilitate reading of the drawings and understanding of the phenomena involved.

[0066] The axial direction is that of the longitudinal axis of the turbomachine, denoted A. The radial direction is perpendicular and coplanar to direction A. The circumferential or tangential direction is orthogonal to the axial direction and to the radial direction.

[0067] The present invention preferably falls within the scope of aircraft turbomachines. In this respect, FIG. 1 schematically represents, in section along a vertical plane passing through its longitudinal axis A, a dual-flow turbojet 1. It comprises from upstream to downstream according to the circulation of the air flow, a fan 2, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6 and a low-pressure turbine 7. It is understood that the invention is not limited to a turbomachine specifically with this structure. [0068] The air entering the turbomachine is cold. It is compressed by the compressors 3 and 4 and rises in temperature to approximately 500-600 °C. At the outlet of the combustion chamber 5, the air is at a temperature of the order of 1500 to 2000 °C. The turbines 6 and 7 therefore see very hot air and are therefore subject to deformation and thermal wear. One way of regulating the temperature of the turbines is to take less hot air, under the combustion chamber 5 and at the level of the last stages of the compressor 4, and to route this air downstream to cool the turbines.

[0069] Figure 2 shows a portion of the turbomachine of Figure 1, and in particular the combustion chamber and seals.

[0070] In the embodiment shown, the turbomachine portion has three seals: a seal 10 downstream of the high pressure compressor (“CDP”), a front internal seal 12 (“FIS”), and a front external seal 14 (“FOS”).

[0071] Figure 2 is only one example of a configuration for an air cooling path in a turbomachine, and the person skilled in the art will be able to identify the respective CDP, FIS and FOS seals in other cooling circuit geometries.

[0072] In the embodiment shown, an air inlet 9 makes it possible to take air 16 downstream of the last compressor disk. The air 16 taken downstream of the last compressor disk first passes through the seal 10, which is located radially below the inlet of the combustion chamber 5.

[0073] The air 16 continues its path in a conduit 11 which can be annular around the axis A.

[0074] The air then passes through a second seal (front internal seal) 12 and opens into a housing 13 arranged between the second seal 12 and a third seal (front external seal) 14.

[0075] Air is also taken from under the combustion chamber 5. Air injectors 15 from a cavity 17 under the combustion chamber open into the housing 13.

[0076] The air 16 coming from the compressor and that coming from the injectors 15 meet at the housing 13. This air is then directed towards a cooling circuit 18 of the first stage of the turbine 6 via an outlet 19 of the housing 13. The seal 14 makes it possible to regulate an air outlet from the housing 13 towards a purge circuit 20, axially positioned between a distributor 6.1 and the first mobile turbine wheel 6.

[0077] The flow 18 is intended to cool the turbine and in particular to cool the hollow blades of the turbine 6.

[0078] The quantities of air regulated by the seals 10, 12, 14 are dictated by the clearance between these seals and a respective internal surface 22 radially facing the seals. In the embodiment shown, the surface 22 facing the seals 10, 12, 14 is an external surface of a rotor assembly. [0079] In the following, the seal of the invention will be described with the number 10 but it should be noted that what is described for this seal can also, or alternatively, be applied to the other seals 12, 14.

[0080] Figure 3 shows a joint 10 in front view, perpendicular to direction A.

[0081] The seal 10 is composed of sectors which are distributed in a circumferential direction T around the axis A. Each sector accounts for an angular part of a ring describing 360° around the axis A. Each sector comprises an internal annular sector 30, an external annular sector 60, and a return member 62. The return member 62 is connected to the internal annular sector 30 at a base 64, and the return member 62 is connected to the external annular sector 60 at a base 66.

[0082] The joint 10 can be formed from 8 to 20 sectors.

[0083] The external annular sectors 60 can together form a single ring. The sectorization is in this case purely geometric. Alternatively, the external annular sectors 60 can be formed from separate parts, assembled together.

[0084] The return member 62 may be formed of two blades of a thickness intended to give them a predetermined elasticity, for example between 0.7 and 2.0 mm. The total thickness of the return member may be between 2.5 and 5.0 mm. It is understood that another number of blades (1, 3, 4) or another elastic spring technology may be used.

[0085] The internal annular sectors 30 are spaced from each other by a distance e. This distance is exaggerated in FIG. 3. It is as small as possible to limit air leakage between the sectors, without hindering the free radial movement of the internal annular sectors 30. This distance may be less than 0.3 mm.

[0086] The seal may be a single piece, that is to say that the internal ring sectors 30, the external ring sectors 60, the return members 62 and the bases 64, 66 may be formed from a single piece.

[0087] The internal annular sectors 30 are spaced from a rotor 22 by a clearance j. The seal 10 is designed to provide a predefined clearance j. The predefined clearance may be between 0.1 and 1.0 mm. It is preferably less than 0.2 mm. This clearance corresponds to a target air flow rate for a given engine speed or load.

[0088] If, during operation of the turbomachine, the clearance j becomes too large, the return member 62 will tend to impart a force radially towards the axis A to reduce the clearance j. Conversely, if the clearance j becomes too small, the air flow passing at the interface between the internal ring sector 30 and the rotor 22 will increase in pressure and will tend to move the internal ring sector 30 away from the axis A.

[0089] Figures 4 and 5 illustrate an advantageous embodiment of the internal ring sector 30, in isometric view, respectively from upstream and from downstream. Figures 4 and 5 are described together in the following paragraphs. [0090] The internal ring sector 30 extends circumferentially from one end materialized by the surface 37 in FIG. 4 to another circumferential end materialized by the surface 39 in FIG. 5.

[0091] The internal ring sector 30 may comprise an upstream portion 32 having an external upstream surface 32.1, cylindrical, and an internal upstream surface 32.2. This upstream portion extends from the circumferential end 37 to the circumferential end 39.

[0092] The upstream portion 32 comprises a frontal surface 32.3 which can be inclined relative to the axis A (and therefore frustoconical).

[0093] The internal ring sector 30 may comprise an upstream lip 42 whose function will be described below. This extends upstream and towards the axis A. The upstream lip 42 has a distal end 42.1 which may be chamfered.

[0094] The lip 42 and the front surface 32.3 may form an angle (a in FIG. 6) which may be greater than or equal to 90°. The lip 42 and the front surface 32.3 may each be inclined at an angle of at least 45° relative to the longitudinal direction A.

[0095] The inner ring sector 30 may include an outer central lip 44 which projects outwardly from the outer upstream surface 32.1.

[0096] Downstream of the lip 44, a downstream portion 46 comprises an external downstream surface 46.1 comprising a first cylindrical surface 46.11 and a second cylindrical surface 46.12. These cylindrical surfaces 46.11, 46.12 have a different radius. The second cylindrical surface 46.12 has a radius smaller than the radius of the first cylindrical surface 46.11. A connecting surface (46.13 in FIG. 5) connects the first cylindrical surface 46.11 to the second cylindrical surface 46.12.

[0097] Thus, the external central lip 44 is arranged between the external upstream surface 32.1 and the external downstream surface 46.1.

[0098] The outer downstream surface 46.1 does not extend circumferentially over the entire circumferential length of the inner ring sector 30. The outer downstream surface 46.1 is circumferentially delimited by a wall 48 at one end (39 in FIG. 5) and by the base 64 at the other end 37. The wall 48 rises radially to a height greater than that of the first cylindrical surface 46.11 and may rise to a height lower than that of the outer upstream surface 32.1. It has the effect of limiting aerodynamic disturbances (edge effects) and therefore of offering a design which allows good control of the clearance between the seal and the rotor.

[0099] The thickness of the wall 48 may be substantially equal to that of the external central lip 44.

[0100] The base 64 may consist of a radial excess thickness having a substantially cylindrical radially external surface and fillets connecting to the first and second cylindrical surfaces 46.11, 46.12. [0101] The downstream portion 46 may have an internal frustoconical surface 56 extending away from the longitudinal axis A at a downstream end of the internal ring sector 30. The material thickness may be constant over the entire downstream portion 46 and an external conical surface 46.14.

[0102] Upstream of the truncated cone-shaped surface 56, and opposite the second cylindrical surface 46.12, there is an internal downstream cylindrical surface 57.

[0103] The internal ring sector 30 may also comprise an internal central lip 58, extending radially towards the axis A.

[0104] Upstream, a first cavity 53 is delimited by the upstream lip 42 and the internal central lip 58. Downstream, a second cavity 55 is formed axially between the internal central lip 58 and the cylindrical surface 57.

[0105] Figure 6 is a sectional view of the inner ring segment 30 in the plane marked VI in Figure 4. Upstream is on the left and downstream is on the right.

[0106] Air coming from the left of the figure encounters a blocking zone formed by the lip 42 and the front surface 32.3.

[0107] The inclination of the upstream lip 42 relative to the axis A (horizontal direction in FIG. 6) may be between 30° and 60°. The angle formed with the front surface 32.3 may be greater than or equal to 90°. The axial length of the internal surface of the upstream lip 42 may be between 1 and 1.5 mm.

[0108] A portion of the air will flow towards a radially external part of the internal ring sector 30.

[0109] A secondary sealing member 59 may come to bear on the external central lip 44. The secondary sealing member 59 is shown here in dotted lines. It may extend from the upstream portion 32 to the external ring sector (60 in FIG. 3). It may extend from the internal ring sector 30 to the external ring sector 60 and be arranged upstream of the return member 62.

[0110] The secondary sealing member prevents air coming from upstream (on the left in FIG. 6) from axially passing through the seal radially above the inner ring sector 30. In other words, such a secondary sealing member ensures that the only path allowing air to pass through the seal is the (controlled) clearance between the inner surface 32.1 of the inner ring sector 30 and the outer surface 22 of the rotor opposite the seal. The secondary sealing member may for example be chosen from a brush seal, a set of tabs, or a tile.

[0111] The upstream portion 32 of the internal ring sector 30 has a thickness E32, distance between the external upstream surface 32.1 and the first cavity 53 (or the internal surface 32.2).

[0112] The upstream portion 32 has an axial length L32, defined between the upstream end of the internal ring sector 30 and the central lip 44, which is between 40 and 45% of the total axial length L of the internal ring sector 30. The total length L may be between 10 and 50 mm and preferably be at least 15 mm. [0113] In the external downstream part, the two cylindrical surfaces 46.11, 46.12 have a respective radius R1 and R2. The radii are measured relative to the axis A. R1 is different from R2 and R1 is greater than R2. In the illustrated case, R1 is greater than R2. The difference between the two radii can be between 1 and 3 mm.

[0114] The thickness E46 of the downstream portion 46 is constant. That is to say that the distance between the second cavity 55 and the cylindrical surface 46.11 is equal to that between the surface 57 and the surface 46.12. The radial distance between the conical internal surface 56 and the conical external surface 46.14 is constant and is also equal to E46. The value of E46 may be greater than or equal to 1.5 mm. The value of E32 is greater than E46 and may preferably be at least 2 times or at least 3 times the value of E46. In other words, the second thickness E46 is preferably at least 50% less than the first thickness E32.

[0115] Thus, in one embodiment, the distance E46 separating the first cylindrical surface

46.1 1 of the first cavity 53 is equal to the distance E46 separating the first cylindrical surface

46.1 1 of the second cavity 55, and is equal to the distance E46 separating the second cylindrical surface

46.12 of the internal downstream cylindrical surface 57.

[0116] The downstream portion 46 has an axial length L46, defined between the central lip 44 and the downstream end of the internal ring sector 30, which is between 50 and 70% of the total axial length L of the internal ring sector 30.

[0117] The upstream lip 42 and the inner central lip 58 form, between them, a first cavity 53. The upstream lip 42 extends to a radius R3 which is larger than the radius R4 inside the inner central lip 58. Thus, the air rushes into this cavity and creates a pressure which pushes the ring sector 30 radially outwards when the clearance between the ring sector and the rotor 22 is too small. The axial length of the lip 58 can be between 1 and 1.5 mm. R3 can exceed R4 by 0.2 to 0.6 mm. The inner distal end 58.1 of the lip 58 can be chamfered.

[0118] The axial length L53 of the first cavity 53 may be between 40% and 70% of the total axial length L of the internal ring sector 30. It is preferably between 50% and 60% of L.

[0119] The axial length L55 of the second cavity 55 may be less than 10% of the total axial length L of the internal ring sector 30.

[0120] The first cavity 53 axially overlaps (in part) the surfaces 32.1 and 46.1 1 . The surface 46.1 1 axially partially overlaps the first cavity 53 and axially completely overlaps the second cavity 55.

[0121] The axial length L57 of the internal downstream cylindrical surface 57 may be between 15% and 25% of the total axial length L of the internal ring sector 30. Preferably, this length is approximately 20% of the length L. The cylindrical surface 57 may have the same radius R4 as the internal central lip 58. [0122] Generally, L53 and L57 are particularly important for controlling the airflow passing under the inner ring sector 30. The second cavity 55 may be of small axial length and is essentially provided to limit the weight of the assembly.

[0123] The angle formed by the diffuser 46.14, 56 may be less than 15°. The diffuser extends axially over less than 10% of the total axial length L.

[0124] The axial length of the lip 44 may be greater than or equal to 1 mm.

[0125] The radial height of the second cavity 55 (R1-E46-R4) may be less than 2 mm.

[0126] The various internal and external surfaces 32.1, 32.2, 46.1, 56, 57 multiply the contact surfaces with the air and create a lift effect of the internal ring sector 30.

Claims

Claims [Claim 1] An annular sealing gasket (10, 12, 14) comprising a plurality of gasket sectors (30, 60, 62, 64) distributed circumferentially around a longitudinal axis (A), each gasket sector comprising an inner ring sector (30) connected to an outer ring sector (60) by a return member (62), the inner ring sector (30) comprising: a first circumferential end (37) and a second circumferential end (39); an outer upstream surface (32.1), cylindrical, extending circumferentially from the first circumferential end (37) to the second circumferential end (39); an outer downstream surface (46.1) extending circumferentially away from the first and second ends (37, 39), the outer downstream surface (46.1) having a first cylindrical surface (46.11) arranged at a first radial position (R1) and a second cylindrical surface (46.12) arranged at a second radial position (R2) distinct from the first radial position (R1); an outer central lip (44) arranged between the outer upstream surface (32.1) and the outer downstream surface (46.1), the outer central lip (44) extending circumferentially from the first circumferential end (37) to the second circumferential end (39); and an inner frustoconical surface (56) extending away from the longitudinal axis (A) at a downstream end of the inner ring sector (30). [Claim 2] A seal according to claim 1, wherein the external upstream surface (32.1) has an axial length (L32) of between 40 and 45% of the total axial length (L) of the internal ring sector (30) and the external downstream surface (46.1) has an axial length (L46) of between 50 and 70% of the total axial length (L) of the internal ring sector (30). [Claim 3] Joint (10, 12, 14) according to one of the preceding claims, in which a wall (48) arranged at a circumferential end (39) and a base (64) intended to connect the return member (62) to the internal ring sector (30) circumferentially delimit the external downstream surface (46.1). [Claim 4] A seal (10, 12, 14) according to any preceding claim, wherein the inner ring sector (30) comprises an upstream lip (42) projecting upstream and towards the longitudinal axis (A), and an inner central lip (58) projecting radially towards the longitudinal axis (A), the upstream lip (42) and the inner central lip (58) each having a respective distal end (42.1, 58.1) arranged at a respective radius (R3, R4), the radius (R3) of the distal end (42.1) of the upstream lip (42) being greater than the radius (R4) of the distal end (58.1) of the inner central lip (58). [Claim 5] A seal (10, 12, 14) according to claim 4, wherein a first cavity (53) is formed between the upstream lip (42) and the inner central lip (58), the axial length (L53) of the first cavity (53) being between 40 and 70% of the total axial length (L) of the inner ring sector (30). [Claim 6] A seal (10, 12, 14) according to claim 5, wherein a first thickness (E32) is defined by the distance separating the external upstream surface (32.1) from the first cavity (53). and a second thickness (E46) is defined by the distance between the first cylindrical surface (46.1 1 ) and the first cavity (53), the second thickness (E46) being preferably at least 50% less than the first thickness (E32). [Claim 7] Seal (10, 12, 14) according to one of claims 4 to 6, in which the distal end (42.1) of the upstream lip (42) is chamfered. [Claim 8] Seal (10, 12, 14) according to one of claims 4 to 7, in which the internal ring sector (30) comprises a truncated cone-shaped front surface (32.3) which forms with the upstream lip (42) an angle (a) greater than or equal to 90°. [Claim 9] Joint (10, 12, 14) according to one of the preceding claims, in which the internal ring sector (30) comprises an internal downstream cylindrical surface (57) of an axial length (L57) between 15 and 25% of the total axial length (L) of the internal ring sector (30). [Claim 10] A seal (10, 12, 14) according to claim 9 in combination with one of claims 5 to 9, wherein a second cavity (55) is formed axially between the inner central lip (58) and the inner downstream cylindrical surface (57), the axial length (L55) of the second cavity (55) being less than 10% of the total length (L) of the inner ring sector (30). [Claim 11] A seal (10, 12, 14) according to claim 10 in combination with claim 5, wherein a second cavity (55) is formed axially between the inner central lip (58) and the inner downstream cylindrical surface (57), and wherein the distance (E46) separating the first cylindrical surface (46.1 1 ) from the first cavity (53) is equal to the distance (E46) separating the first cylindrical surface (46.1 1 ) from the second cavity (55), and is equal to the distance (E46) separating the second cylindrical surface (46.12) from the inner downstream cylindrical surface (57). [Claim 12] Seal (10, 12, 14) according to one of the preceding claims, further comprising a secondary sealing member (59) arranged radially between the internal ring sector (30) and the external ring sector (60) and arranged upstream of the return member (62), the secondary sealing member (59) bearing on the external central lip (44). [Claim 13] Turbomachine (1) comprising: a high pressure compressor (4); a combustion chamber (5); a high pressure turbine (6); a first, a second and a third seal (10, 12, 14); and a circuit (9-20) for conveying cooling air to the high-pressure turbine (6), the air conveying circuit comprising an air inlet (9) downstream of the high-pressure compressor (4), a duct (11) separated from the inlet (9) by the first seal (10), a housing (13) separated from the duct (11) by the second seal (12), an air injector (15) opening into the housing (13), a purge outlet (20) separated from the housing (13) by the third seal (14) and an air outlet (19) from the housing (13) directing the air flow (18) to the high-pressure turbine (6), at least one of the first, second and third seals (10, 12, 14) being in accordance with any one of claims 1 to 12.