Seal for a turbine engine
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- SAFRAN AIRCRAFT ENGINES SAS
- Filing Date
- 2024-07-26
- Publication Date
- 2026-06-24
Smart Images
Figure FR2024051030_20022025_PF_FP_ABST
Abstract
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. Prior art
[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various carbon emission restrictions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those already in operation, requiring the implementation of technological solutions to ensure their compliance with current regulations. Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.
[0003] Technological research efforts have already led to significant improvements in 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 turbine cooling air can be taken downstream of the compressor and radially inside the combustion chamber. 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 material of the stator. The abradable material can have a honeycomb-type alveolar structure.
[0007] The disadvantage of this type of seal is that the friction of the wipers on the abradable material tends to damage the abradable material and consequently increase the clearance between rotor and stator. This leads to an increase in the airflow through the seals. Depending on the seal in question (CDP, FIS, FOS), this means an increase or decrease in the airflow supplied to the turbines and therefore a deviation from a target airflow value. Thus, increasing 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 provide a turbomachine seal which makes it possible to control the flow of cooling air supplied to the turbines, regardless of its service life.
[0010] To this end, the present document relates to an annular sealing joint comprising a plurality of seal sectors distributed circumferentially around a longitudinal axis, each seal sector comprising an inner ring sector connected to an outer ring sector by a return member, the inner ring sector comprising: a core; an outer upstream platform and an inner upstream platform, both extending from the projecting core upstream, and being arranged radially at a distance from each other; and an outer downstream platform and an inner downstream platform, both extending from the projecting core downstream, and being arranged radially at a distance from each other.
[0011] This seal architecture differs from a labyrinth seal. The platforms have surfaces (respectively upper and lower) that multiply the air bearing surfaces on the seal. The lift of the inner sector on these surfaces ensures that a predefined clearance with the inner rotor is maintained. The design of the inner ring sector thus allows hydrostatic self-regulation of the position of the inner 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 with respect to a spring behavior of the internal ring sectors ensured in particular by the return members and the airflow.
[0014] More precisely, if the clearance between the seal and the rotor becomes smaller than the preset clearance, the air friction on the platforms tends to move the inner ring sector from so as to increase the clearance. Conversely, if the clearance between the seal and the rotor becomes greater than the predefined clearance, the return member exerts a force greater than the lift of the platforms, the internal ring sectors then returning to their equilibrium positions, i.e. to the predefined clearance.
[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 wear problem encountered with conventional labyrinth seals.
[0016] The "circumferential distribution" of the seal sectors is intended to mean that each seal sector defines a portion of the seal circumference, and that the set of seal sectors together makes it possible to obtain the complete seal. Optionally, the distribution is regular and each seal sector then represents an equal portion of the seal circumference.
[0017] The terms "internal" and "external", or interchangeably "inside" and "outside", refer to a radial position relative to the 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 in a turbomachine.
[0018] According to one embodiment, the inner ring sector comprises an upstream lip extending projecting upstream from an upstream end of the inner upstream platform and being inclined away from the outer upstream platform.
[0019] The lip diverges upstream and thus allows a greater volume of air to be "captured" and brought into the cavity formed radially between the upstream platforms.
[0020] According to one embodiment, the upstream platforms are connected to each other and / or the downstream platforms are connected to each other, by a central reinforcement arranged circumferentially in a central position of the internal ring sector and / or by two lateral reinforcements arranged circumferentially at the circumferential ends of the internal ring sector.
[0021] These reinforcements help to stiffen the structure and stabilize the circumferential position of the internal ring sector, thus resulting in better control of the clearance between the seal and the rotor.
[0022] According to one embodiment, the return member is connected to the internal ring sector at a base which is arranged at a circumferential end of the external downstream platform. Alternatively, the return member can be connected to the internal ring sector at a base which is arranged at a circumferential end of the external upstream platform.
[0023] By connecting the return member to a circumferential end, it is possible to use flexible return members which do not lose their elasticity through fatigue, allowing good control of the clearance to be maintained even when the joint is worn.
[0024] According to one embodiment, the outer downstream platform has an outer surface and the outer upstream platform has an inner surface, the outer surface of the outer downstream platform being closer to the longitudinal axis than the inner surface of the outer upstream platform.
[0025] According to one embodiment, the inner ring sector comprises an outer central lip extending radially with respect to the longitudinal axis projecting from the core.
[0026] This 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.
[0027] According to one embodiment, the seal further comprises a secondary sealing member arranged radially between the inner ring sector and the outer ring sector and arranged upstream of the return member, the secondary sealing member bearing on the outer central lip.
[0028] The secondary sealing member prevents air from axially passing through the seal radially 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.
[0029] 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.
[0030] According to one embodiment, the inner ring sector comprises an inner central lip extending radially with respect to the longitudinal axis and projecting from the core.
[0031] This internal lip forms an obstacle to air flow which, when the clearance is less than the preset clearance, allows the pressure at the interface between the seal and the rotor to be increased, in order to help push the seal radially outwards and assist in restoring the preset clearance.
[0032] According to one embodiment, the axial length of the upstream platforms is between 30% and 50% of the total axial length of the internal ring sector.
[0033] Such a ratio is seen as sufficient for the platforms to operate their hydrostatic function without unnecessarily increasing the weight or bulk of the seal.
[0034] According to one embodiment, the axial length of the internal downstream platform is less than 40% of the total axial length of the internal ring sector and the axial length of the external downstream platform is at least equal to the axial length of the internal downstream platform.
[0035] According to one embodiment, the radial thickness of the platforms is greater than 1 mm.
[0036] Thus, the platforms have sufficient rigidity so that the design of the return member and the dimensions of the platforms are robust: platforms that are too thin could deform during use and prevent precise control of the clearance during the life of the seal.
[0037] In one embodiment, the outer ring sectors form an outer shell and the inner ring sectors have ends arranged end-to-end in the circumferential direction.
[0038] 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°.
[0039] An inclination of the ends of the inner ring sectors makes it possible to reduce the clearance existing between two inner ring sectors, thus improving the effectiveness of the sealing joint.
[0040] In one embodiment, the seal comprises between 8 and 20 seal sectors.
[0041] This range of values represents a good compromise between too few sectors, which means heavy sectors for the recall devices, and too many sectors, which means many inter-sector gaps and therefore potential air leaks.
[0042] In one embodiment, the outer ring sectors of a seal may be a single piece, for example a ferrule. In other words, there is no physical separation between two circumferentially successive outer ring sectors.
[0043] 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.
[0044] 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 bleed outlet separated from the housing by the third seal and an air outlet from the housing directing the air flow to the high-pressure turbine, at least one of the first, second and third seals being in accordance with one of the embodiments set out above.
[0045] 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 internal seal (called "FIS" for "forward inner seal" in English) and the third seal is a forward external seal (called "FOS" for "forward outer seal" in English).
[0046] 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
[0047] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which:
[0048] [Fig. 1] is a schematic sectional view of a turbomachine;
[0049] [Fig. 2] is a sectional view of a turbine cooling circuit;
[0050] [Fig. 3] is a front view of a seal according to the invention;
[0051] [Fig. 4] is an upstream isometric view of an inner ring sector;
[0052] [Fig. 5] is a downstream isometric view of an inner ring sector;
[0053] [Fig. 6] is a sectional view of an inner ring sector. Description of the embodiments
[0054] The figures depict various aspects of the invention schematically. The dimensions are not drawn to scale: some dimensions are enlarged to facilitate reading the drawings and understanding the phenomena involved.
[0055] The axial direction is that of the longitudinal axis of the turbomachine, noted 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.
[0056] The present invention preferably falls within the scope of aircraft turbomachines. In this respect, Figure 1 schematically represents, in section along a vertical plane passing through its longitudinal axis A, a double-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.
[0057] The air entering the turbomachine is cold. It is compressed by compressors 3 and 4 and rises in temperature to approximately 500-600°C. At the outlet of combustion chamber 5, the air is at a temperature of around 1500 to 2000°C. 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 cooler air, radially inside combustion chamber 5 and at the level of the last stages of compressor 4, and to route this air downstream to cool the turbines.
[0058] Figure 2 represents a portion of the turbomachine of Figure 1, and in particular the combustion chamber and seals.
[0059] 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”).
[0060] Figure 2 is only one example 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.
[0061] In the embodiment shown, an air inlet 9 makes it possible to take air 16 downstream of the last compressor disc. The air 16 taken downstream of the last compressor disc first passes through the seal 10, which is located radially internally relative to the inlet of the combustion chamber 5.
[0062] The air 16 continues its path in a conduit 11 which can be annular around the axis A.
[0063] 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.
[0064] Air is also taken radially inwardly relative to the combustion chamber 5. Air injectors 15 coming from a cavity 17 radially inwardly relative to the combustion chamber open into the housing 13.
[0065] 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 turbine wheel 6.
[0066] Flow 18 is intended to cool the turbine and in particular to cool the hollow blades of turbine 6.
[0067] 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 facing the seals. In the embodiment shown, the surface 22 facing the seals 10, 12, 14 is an external surface of a rotor assembly.
[0068] 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.
[0069] Figure 3 shows a seal 10 in front view, perpendicular to direction A.
[0070] 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.
[0071] Joint 10 can be formed from 8 to 20 sectors.
[0072] The outer annular sectors 60 may together form a single ring. The sectorization is in this case purely geometric. Alternatively, the outer annular sectors 60 may be formed from separate pieces, assembled together.
[0073] 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.
[0074] The inner annular sectors 30 are spaced apart from each other by a distance e. This distance is exaggerated in Figure 3. It is as small as possible to limit air leakage between the sectors, without hindering the free radial movement of the inner annular sectors 30. This distance may be less than 0.3 mm.
[0075] The seal may be a single-piece seal, i.e. the inner ring sectors 30, the outer ring sectors 60, the return members 62 and the bases 64, 66 may be formed from a single piece.
[0076] 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.
[0077] If, during operation of the turbomachine, the clearance j becomes too large, the return member 62 will tend to apply 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.
[0078] Figures 4 and 5 illustrate an advantageous embodiment of the internal ring sector 30, in isometric view, respectively from upstream and from downstream.
[0079] The inner ring sector 30 may comprise a core 31, i.e. a solid element forming the core of the inner ring sector 30 and from which various structural elements of the inner ring sector 30 extend. In this example, the core 31 is curved around the axis A.
[0080] The inner ring sector 30 may comprise an outer upstream platform 32 and an inner upstream platform 34. These platforms 32, 34 are curved according to the curvature around the axis A. They are arranged upstream of the core 31. They are separated from each other in the radial direction. A recess 36 is thus formed between the platforms 32, 34. The inner platform 34 may be slightly set back axially, for example by 5 to 10% of the axial length of the platform 32 (see figure 6).
[0081] The internal ring sector 30 extends circumferentially from one end materialized by the surface 37 to another circumferential end materialized by the surface 39. The platforms 32, 34 extend circumferentially from one end 37 of the internal ring 30 to the other 39.
[0082] The inner ring sector 30 may be reinforced by reinforcements connecting the outer upstream platform 32 to the inner upstream platform 34. The reinforcements may comprise a central reinforcement 38, arranged circumferentially at an intermediate position of the inner ring sector 30, which intermediate position may be substantially in the middle of the inner ring sector 30. The central reinforcement 38 divides the recess 36 in two. The reinforcements may additionally or alternatively comprise lateral reinforcements 40 at the circumferential ends of the inner ring sector 30. The recess 36 is thus circumferentially delimited.
[0083] When the internal upstream platform 34 is axially set back from the external upstream platform 36, the reinforcements 38 and 40 may have an upstream surface which is inclined relative to the axis A at an angle which may be between 30 and 80°.
[0084] The internal ring sector 30 may comprise an upstream lip 42 extending from the upstream end 34.3 of the internal upstream platform 34, the function of which will be described below. This lip extends upstream in a flared direction. It may form an angle of between 30 and 60° relative to the axis A. The angle of inclination of the lip 42 may possibly be identical to the angle formed by the reinforcements 38, 40 with the axis A.
[0085] The inner ring sector 30 may comprise a lip 44 which projects from the core 31 radially outwardly from the axis A.
[0086] Seen from downstream, Figure 5 shows that the inner ring sector 30 may comprise an outer downstream platform 46 and an inner downstream platform 48. These platforms 46, 48 are curved according to the curvature around the axis A. They are arranged downstream of the core 31. The outer downstream platform 46 may be radially spaced from the inner downstream platform 48. A recess 50 is thus formed. The platforms 46, 48 extend circumferentially from one end 37 of the inner ring 30 to the other 39.
[0087] The inner ring sector 30 may be reinforced by reinforcements connecting the outer downstream platform 46 to the inner downstream platform 48. The reinforcements may comprise a central reinforcement 52, arranged circumferentially at an intermediate position of the inner ring sector 30, which intermediate position may be substantially in the middle of the inner ring sector 30. The central reinforcement 52 divides the recess 50 in two. The reinforcements may additionally or alternatively comprise lateral reinforcements 54 at the circumferential ends of the inner ring sector 30. The recess 50 is then circumferentially delimited.
[0088] The reinforcements 38, 40, 52, 54 have a thickness (in the circumferential direction) which may be between 1% and 10% of the circumferential length of the internal ring sector 30.
[0089] The internal downstream platform 48 may have an internal surface that becomes thinner, forming for example a truncated cone 56.
[0090] The inner ring sector 30 may also comprise an inner central lip 58, extending from the core 31 radially towards the axis A.
[0091] In summary, the inner ring sector 30 comprises: a core 31; an outer upstream platform 32 and an inner upstream platform 34, both extending from the core 31 projecting upstream, and being arranged radially at a distance from each other; and an outer downstream platform 46 and an inner downstream platform 48, both extending from the core 31 projecting downstream, and being arranged radially at a distance from each other.
[0092] Figures 4 and 5 also highlight the presence of the base 64, the place of attachment of the return member 62. The base can advantageously be arranged at a circumferential end of the internal ring sector 30. The base 64 can consist of a radial excess thickness having a substantially cylindrical radially external surface and fillets for connection to the external surface of the external downstream platform. The base 64 is here shown on the external downstream platform 46 but it can alternatively be provided on the external upstream platform.
[0093] Figure 6 is a sectional view of the inner ring segment 30 in the plane denoted VI in Figure 4.
[0094] The external upstream platform 32 has an external surface 32.1 and an internal surface 32.2. The thickness of the external upstream platform 32, denoted E32, is the distance between the external surface 32.1 and the internal surface 32.2.
[0095] The internal upstream platform 34 has an external surface 34.1 and an internal surface 34.2. The thickness of the internal upstream platform 34, denoted E34, is the distance between the external surface 34.1 and the internal surface 34.2.
[0096] The external downstream platform 46 has an external surface 46.1 and an internal surface 46.2. The thickness of the external downstream platform 46, noted E46, is the distance between the external surface 46.1 and the inner surface 46.2. The outer surface 46.1 of the outer downstream platform 46 may be closer to the longitudinal axis A than the inner surface 32.2 of the outer upstream platform 32.
[0097] The internal downstream platform 48 has an external surface 48.1 and an internal surface 48.2. The thickness of the internal downstream platform 48, noted E48, is the distance between the external surface 48.1 and the internal surface 48.2.
[0098] Thicknesses E32, E34, E46 and E48 can be greater than 1 mm.
[0099] The respective lengths of the platforms 32, 34, 46 and 48 are denoted L32, L34, L46 and L48. The length L34 is between 20% and 70%, and preferably between 30% and 50% of the total axial length of the joint, denoted L. The value of L can be between 10 and 50 mm. It is preferably greater than 15 mm. The length L32 is greater than or equal to L34.
[0100] The length L48 is less than 60%, and preferably less than 40% of the length L. The length L46 is greater than or equal to the length L48.
[0101] The recesses 36 and 50 have a respective radial height E36 and E50, greater than 1 mm. Their radial height can be constant.
[0102] A secondary sealing member 59 may bear against the external central lip 44. The secondary sealing member 59 is shown here in dotted lines. It may extend from the external upstream platform 32 to the external ring sector (60 in FIG. 3). It may be arranged upstream of the return member 62.
[0103] The secondary sealing member prevents air coming from upstream (on the left in Figure 6) from axially passing through the seal radially outwardly relative to 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 clearance j (controlled), shown in Figure 3, between the inner surface 34.2, 48.2 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.
[0104] The external central lip 44 may have an upstream projection which is materialized by a baffle 44.1 further reinforcing the seal in this area.
[0105] The various internal and external surfaces of the platforms 32, 34, 46, 48 multiply the contact surfaces with the air and create a lift effect of the internal ring sector 30.
[0106] The upstream lip 42 and the inner central lip 58 form obstacles to the flow of air which generate an overpressure on the inner surfaces. The inclination of the upstream lip 42 relative to the axis A (horizontal direction in FIG. 6) can be between 30° and 60°. The radial clearance between the lip 42 and the rotor is greater than that between the inner central lip 58 and the rotor in order to ensure an air cushion effect, the air arriving more easily in the cavity between the lip 42 and the lip 58 than it escapes therefrom.
[0107] Downstream, the truncated cone 56 has a diffuser function, limiting the air flow passing through the seal. The inclination of the truncated cone can be between 20° and 45° relative to the axis A. Too small an angle limits the diffusion effect and too large an angle reduces the lift on the internal ring sector 30. If the lip 42 and the truncated cone 56 have their own local repercussions on the flow of the air flow, these elements also have a synergy in the mechanical balance of the internal ring sector 30, allowing it to maintain its orientation relative to the axis A.
[0108] In a variant not illustrated, the internal ring sector 30 is devoid of upstream platforms or is devoid of downstream platforms.
Claims
Claims
1. An annular seal (10, 12, 14) comprising a plurality of seal sectors (30, 60, 62, 64) distributed circumferentially around a longitudinal axis (A), each seal 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 core (31); an outer upstream platform (32) and an inner upstream platform (34), both extending from the core (31) projecting upstream, and being arranged radially at a distance from each other; and an outer downstream platform (46) and an inner downstream platform (48), both extending from the core (31) projecting downstream, and being arranged radially spaced from each other.
2. A seal (10, 12, 14) according to claim 1, wherein the inner ring sector (30) comprises an upstream lip (42) extending projecting upstream from an upstream end (34.3) of the inner upstream platform (34) and being inclined away from the outer upstream platform (32).
3. Joint (10, 12, 14) according to one of the preceding claims, in which the upstream platforms (32, 34) are connected to each other and / or the downstream platforms (46, 48) are connected to each other, by a central reinforcement (38, 52) arranged circumferentially in a central position of the internal ring sector (30) and / or by two lateral reinforcements (40, 54) arranged circumferentially at the circumferential ends (37, 39) of the internal ring sector (30).
4. Joint (10, 12, 14) according to one of the preceding claims, in which the return member (62) is connected to the internal ring sector (30) in a base (64) which is arranged at a circumferential end (37, 39) of the external downstream platform (46).
5. Joint (10, 12, 14) according to one of the preceding claims, in which the external downstream platform (46) has an external surface (46.1) and the external upstream platform (32) has an internal surface (32.2), the external surface (46.1) of the external downstream platform (46) being closer to the longitudinal axis (A) than the internal surface (32.2) of the external upstream platform (32).
6. Seal (10, 12, 14) according to one of the preceding claims, in which the internal ring sector (30) comprises an external central lip (44) extending radially with respect to the longitudinal axis (A) projecting from the core (31).
7. Seal (10, 12, 14) according to the preceding claim, further comprising a secondary sealing member (59) arranged radially between the inner ring sector (30) and the outer ring sector (60) and arranged upstream of the return member (62), the secondary sealing member (59) bearing on the outer central lip (44).
8. Seal (10, 12, 14) according to one of the preceding claims, in which the internal ring sector (30) comprises an internal central lip (58) extending radially with respect to the longitudinal axis (A) and projecting from the core (31).
9. Joint (10, 12, 14) according to one of the preceding claims, in which the axial length (L32, L34) of the upstream platforms (32, 34) is between 30% and 50% of the total axial length (L) of the internal ring sector (30).
10. Joint (10, 12, 14) according to one of the preceding claims, in which the axial length (L48) of the internal downstream platform (48) is less than 60% and preferably less than 40% of the total axial length (L) of the internal ring sector (30) and the axial length (L46) of the external downstream platform (46) is at least equal to the axial length (L48) of the internal downstream platform (48).
11. Joint (10, 12, 14) according to one of the preceding claims, in which the radial thickness (E32, E34, E46, E48) of the platforms (32, 34, 46, 48) is greater than 1 mm.
12. 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 11.