BE1026058B1 - GASKET FOR AXIAL TURBOMACHINE COMPRESSOR - Google Patents

Abstract

The invention relates to a sealing system (36) for a turbomachine, in particular for a low-pressure compressor, also called a booster. The sealing system comprising: an annular array of rotor vanes (24) with outer edges (40) at radial ends; an external support forming a housing with an internal groove; a kevlar ribbon (34) defining a radial clearance (46) with the outer edges of the rotor vanes; resilient means (38) such as polymeric foam, blades or wires, resiliently connecting the ribbon to the outer support. Depending on the circumference, the outer edges (40) comprise rounded profiles (52) radially facing the ribbon. The invention also relates to a method of operating a turbomachine, such as a turbojet engine or a turboprop, with a sealing system.

Description

Description

GASKET FOR TURBOMACHINE COMPRESSOR

AXIALE

Technical area

The invention relates to a seal around a row of rotor blades. More specifically, the invention relates to a compressor provided with an annular seal between a ferrule and movable blade heads. The invention also relates to an axial turbomachine, in particular an aircraft turbojet or an aircraft turboprop. The invention provides a method of operating a turbomachine with a sealing system.

Prior art

Document EP2495399A1 discloses a turbojet engine comprising a compressor with an external casing. The casing envelops the ends of a row of blades of the compressor rotor. It includes a structural wall; a segmented ferrule intended to surround the row of vanes and supported by the wall, and elastic means arranged between the wall and the segments of the ferrule so as to allow said segments to move radially in the event of contact with the ends of rotor blades, in particular in the event of misalignment of the axis of rotation of the rotor with respect to the axis of the casing.

However, the wear phenomena are particularly marked at the interface between the blades and the outer shell. In use, the radial clearance between the blades and the casing increases, and the amount of leakage increases during the life of the compressor.

Summary of the invention

Technical problem

The object of the invention is to solve at least one of the problems posed by the prior art. More specifically, the invention aims to extend the life of a sealing system. The invention also aims to provide a simple, resistant, light, economical, reliable, easy to produce, and convenient maintenance solution.

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Technical solution

The subject of the invention is a sealing system for a turbomachine, in particular for a turbomachine compressor, the sealing system comprising: an annular row of rotor blades with external edges; an external support; a ribbon defining radial clearances against the outer edges of the rotor blades; elastic means connecting elastically the ribbon to the external support; remarkable in that perpendicular to the axis of rotation of the turbomachine, the outer edges of the blades include rounded profiles which are radially opposite the ribbon.

According to advantageous modes of the invention, the system can include one or more of the following characteristics, taken in isolation or according to all the possible technical combinations:

- The elastic means include internal recesses.

- The elastic means have an axial stiffness, and a radial stiffness less than the axial stiffness.

- The elastic means include studs distributed along the circumference, the number of studs exceeds by at least 10% the number of rotor blades in the annular row.

- The elastic means include clearances distributed along the circumference, in particular distributed between the studs.

- The elastic means comprise sets of elastic blades, possibly separated from each other.

- The elastic blades of each set intersect.

- The elastic means include blocks of polymer foam.

- The elastic means comprise elastic threads.

- Each radial clearance has a radial height H which varies according to the circumference of the same associated rounded profile.

- The support comprises a sealed annular groove in which the ribbon and the elastic means are completely housed.

- The coefficient of friction between the outer edges of the blades and the ribbon is less than the coefficient of friction between the outer edges of the blades and the support, and / or less than the coefficient of friction between the outer edges

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BE2018 / 5120 of blades and the elastic means, possibly the tape is or includes an anti-friction coating.

- The ribbon is made of polymer material.

- The ribbon is made of kevlar.

- The ribbon is segmented according to its circumference.

- The elastic means comprise piezoelectric sensors, and the system comprises a module for detecting the deformation of the ribbon.

- The thickness of the ribbon is less than the average thickness of the rotor blades, especially the average thickness of the outer edges.

- The elastic means are mostly empty, in particular at least 80% or 90% empty; these voids being in particular formed by the recesses.

- The elastic means have a circumferential stiffness greater than the radial stiffness, at least two or five times lower.

- The outer edges form / are the radial ends of the blades.

- The clearances separate the studs, and / or form an alternation with the studs according to the circumference.

- Each stud extends over the entire axial length of the groove.

- Each rotor blade comprises a radial stack of aerodynamic profiles formed along planes perpendicular to the planes in which its rounded profiles are formed.

- The vertices or each vertex of the outer edge of the blade forms a curved line which follows the inner surface of the ribbon.

- The system comprises an annular vein, in particular crossed by the primary flow, the ribbon being in contact with the vein.

- The wall of the support is of constant thickness.

- The housing has a constant radial thickness between the annular rows of stator vanes.

The invention also relates to a turbomachine, in particular an aircraft turbojet engine capable of ingesting a volatile, the turbomachine comprising a sealing system, remarkable in that the sealing system conforms to the invention, preferably the compressor is a low pressure compressor.

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The invention also relates to a method of operating a turbomachine with a sealing system, the sealing system comprising: an annular row of rotor blades with external edges; an external support; a ribbon defining radial clearances with the outer edges; elastic means connecting elastically the ribbon to the external support; the method comprising the following steps: (b) rotation of the rotor vanes inside the ribbon; (c) radial contact of the outer edges of the rotor blades with the ribbon; remarkable in that, depending on the thickness of the blades, in particular along the circumference, the outer edges of the blades comprise rounded profiles of radius R and radially facing the ribbon; and in that during step (c) contact the or each radius R remains constant, the system possibly being in accordance with the invention.

According to advantageous modes of the invention, the process can include one or more of the following characteristics, taken in isolation or according to all possible technical combinations:

- During step (c) contact, the blade edges touch a contact zone of the ribbon, and in that during step (c) contact, the thickness of the contact zone of the ribbon remains constant.

- The contact area is arched and / or describes an angle of at most 180 °.

- During step (c) contact, the radial height of the edges remains constant.

- Step (a) stop is performed before step (b) rotation and / or after step (c) contact.

- Each blade includes a leading edge, a trailing edge, a central part axially between the leading edge and the trailing edge, the radius R decreasing from the central part towards the leading edge and towards the leading edge. leak.

- The aerodynamic profiles of the blades are bent according to second rays R2 at least ten times greater than the radius R.

In general, the advantageous modes of each object of the invention are also applicable to the other objects of the invention. Each object of the invention can be combined with the other objects, and the objects of the invention can also be combined with the embodiments of the description, which in addition

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BE2018 / 5120 are combinable with each other, in all possible technical combinations, unless the opposite is explicitly mentioned.

Benefits

The resistance decreases in case of contact between the ribbon and the blade tips. Indeed, the radial crushing of the elastic means is preferred since they form a flexible sub-layer.

In addition, the containing aspect of the edges of the blades is reduced so that their aggressiveness towards the ribbon disappears. In addition, the area of the radial faces of the outer edges coming into contact with the tape decreases. This further reduces friction, and offers a synergistic effect useful for the longevity of the sealing system.

The elastic means offered offer reduced radial stiffness, while optimizing the axial and circumferential stiffness. These configurations limit wear at the ribbon and blade edges, again improving the longevity of the system. The choice of kevlar material is also part of this perspective.

The porous or hollowed out appearance of the elastic means allows air circulation in the groove along the circumference. Otherwise, when in contact with a rotor vane moving at 300 m / s, the air contained in the groove would radially brake the ribbon. This would increase the friction between the ribbon and the blades.

Brief description of the drawings

FIG. 1 represents an axial turbomachine according to the invention.

FIG. 2 is a diagram of a turbomachine compressor according to the invention.

Figure 3 illustrates a sealing system according to the invention.

Figure 4 shows the radial clearance between a blade edge and the ribbon according to the invention.

Figure 5 shows an outer blade edge according to the invention.

Figure 6 sketches a set of blades according to the invention.

Figure 7 sketch of elastic threads according to the invention.

Figure 8 sketches a block of foam according to the invention.

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FIG. 9 is a diagram of an operating method of a turbomachine according to the invention.

Description of the embodiments

In the following description, the terms "internal" and "external" refer to a positioning relative to the axis of rotation of an axial turbomachine. The axial direction corresponds to the direction along the axis of rotation of the turbomachine. The radial direction is perpendicular to the axis of rotation. Upstream and downstream are in reference to the main flow direction of the flow in the turbomachine.

Figure 1 shows a simplified axial turbomachine. In this specific case, it is a dual-flow turbojet engine propelling an aircraft. The turbojet engine 2 comprises a first level of compression, called a low-pressure compressor 4, a second level of compression, called a high-pressure compressor 6, a combustion chamber 8 and one or more levels of turbines 10. In operation, the mechanical power of the turbine 10 transmitted via the central shaft to the rotor 12 sets in motion the two compressors 4 and 6. The latter comprise several rows of rotor blades associated with rows of stator blades. The rotation of the rotor around its axis of rotation 14 thus makes it possible to generate an air flow and to gradually compress the latter until the inlet of the combustion chamber 8.

An inlet fan commonly designated as a fan or blower 16 is coupled to the rotor 12 and generates an air flow which is divided into a primary flow 18 passing through the various aforementioned levels of the turbomachine, and into a secondary flow 20 passing through an annular duct. (partially shown) along the machine to then join the primary flow at the turbine outlet.

Reduction means 17, such as a planetary reduction gear, can reduce the speed of rotation of the blower and / or of the low pressure compressor relative to the associated turbine.

Figure 2 is a sectional view of a compressor of an axial turbomachine such as that of Figure 1. The compressor can be the low pressure compressor 4. One can observe a part of the fan 16 and the separation nozzle 22 primary flow 18 and secondary flow 20. The rotor 12

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BE2018 / 5120 7 comprises several rows of rotor blades 24, in this case three. It can be a padded monobloc drum, or include dovetail-fixing vanes.

The low-pressure compressor 4 comprises several rectifiers, in this case four, each containing a row of stator vanes 26. Some stator vanes can be of adjustable orientation, also called variable-pitch vanes, or "VSV". The stator vanes 26 extend essentially radially from an external casing 28 forming their external support, and can be fixed and immobilized there using pins. Optionally, the casing 28 is formed of several rings, or half shells; for example in composite material.

Within a single row, the blades (24; 26) are regularly spaced from each other, and have the same angular orientation in the flow. Advantageously, the blades of the same row are identical. Each row can comprise at least: 50, or 80, or 120 blades, in particular identical.

Around the rows of rotor vanes 24, the casing 28 or more precisely its annular wall 30, has annular grooves 32. These grooves 32 sink radially into the radial thickness of the casing. They can be opened radially towards the axis of rotation 14; either inward. The grooves 32 can remain in the thickness of the wall 30, so that the radial thickness of the casing - respectively of the stator - remains constant. This compactness respects the constraints of integration into a compressor, in particular low pressure.

Ribbons 34 can be placed in the grooves 32. These ribbons 34 can form loops around the rotor 12, in particular around the rotor vanes 24. By marrying them, the ribbons 34 limit leakage at the outer edges of blades or heads of vanes, thus forming sealing systems 36. The sealing can be a dynamic sealing in the sense that it becomes effective during the rotation of the rotor 12, possibly accompanied by its deformation by centrifugal force and / or its expansion.

In addition, the sealing systems 36 may include elastic means 38 arranged in the grooves 32, and fixing the tapes 34 therein so

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BE2018 / 5120 flexible in order to adapt to the impacts of the blades 24. Each ribbon 34 can form a closed loop around its row of blades 24.

Figure 3 shows a sealing system 36, for example as shown in Figure 2. The system 36 is shown in section along the axis 3-3 plotted in Figure 2. The section can be perpendicular to the axis of rotation 14 (whose position is fictitious). Several external edges 40 of vanes 24 are shown, the latter passing through the primary flow 18.

The elastic means 38 extend radially from the annular wall 30 forming their support, towards the external edges 40. The ribbon 34 is placed at their radial interface and separates them by forming a tight skin, so that in case of contact the external edges 40 touch the ribbon 34 while remaining at a distance from the elastic means 38.

The elastic means 38 can form studs 42. These studs 42 can be separated from each other by circumferential clearances 44, or angular separations. The clearances can axially cut the means into studs. The studs 42 like the clearances 44 can be distributed circumferentially. They can alternate according to the circumference. The clearances 44 can pass radially through the annular groove 32 up to the strip 34.

Thus, the elastic means form an elastic sub-layer, in particular discontinuous along the circumference. Within each sealing system 36, the number of vanes 24 may be less than that of the studs 42, for example by at least 10%, 20% or 50%. Thus, each stud 42 is in contact with only one blade 24 at a time, and its deformations are better managed.

The elastic means 38, in particular the studs 42, can extend over the entire axial length of the groove 32. Depending on the circumference, the studs 42 can be wider, for example at least twice as wide as the clearances 44. Optionally, one or more clearances can cut the ribbon so as to segment it.

The system 36 can include piezoelectric sensors 78. These piezoelectric sensors 78 can be placed in the elastic means 38, in particular inside the studs 42. A detection module 80 can be

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BE2018 / 5120 connected or communicate with the piezoelectric sensors 78 in order to detect and quantify the deformation of the ribbon 34.

FIG. 4 shows an enlargement of the sealing system 36 between an outer edge 40 of the blade 24 and the ribbon 34 which covers the elastic means 38, in particular a stud 42. The enlargement may be a section perpendicular to the axis of rotation 14. The thickness of the edge 40 may be greater than that of the tape 34.

The outer edge 40 forming the end of the blade 24 is rounded in this section plane. A radial clearance 46 is present between the internal surface 48 of the tape 34 and the edge 40. In operation, the edge 40 touches the internal surface 48, closing the radial clearance 46. It may have a radius R, also called the first radius R, for example measured around a line 50 substantially parallel to the axis of rotation 14.

By scanning the rounded profile 52 of the edge 40 along the circumference 54, the radial height H of the radial clearance 46 varies. The rounded profile 52 can comprise a curve or a convex surface in contact with the clearance 46. The radial height H of the clearance 46 can be defined between the internal surface 48 and the rounded 52 and / or against the edge 40. The apex 56 of the edge 40, in particular of rounding 52, forms the point closest to surface 48.

FIG. 5 sketches an outer edge 40 of the blade 24 seen from the outside, towards the axis of rotation 14. The primary flow 18 in which the blade 24 is bathed. The rotor vane 24 can correspond to those presented in FIGS. 1 to 4.

The blade 24 is formed of a radial stack of aerodynamic profiles 58, only one being shown here. Each aerodynamic profile 58 extends from the leading edge 60 to the trailing edge 62 of the blade 24. Each aerodynamic profile 58 can be arched, the lower surface 64 can be curved.

The average line 66 of the aerodynamic profile 58, can follow a line defined by the vertices 56 of the outer edge 40, and can have a second radius R2. The second radius R2 is defined in a plane orthogonal to those in which the first rays are defined. The second radius R2 is greater than or equal to at least twenty times the or each first radius. Possibly, rounding 52

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BE2018 / 5120 narrows towards the leading edge 60 and trailing edge 62, being notably accompanied by a reduction in the first radius.

FIG. 6 sketches the elastic means 36. They can comprise elastic blades 70 forming a stud 42 in contact with the tape 34. The blades 70 can be made of metal, for example spring steel.

The blades 70 form a set of blades. They can cross. Each blade may include one end linked to the ribbon 34, and another end linked in the groove to the support, in particular the casing or the annular wall. Recesses 72 can be made between the blades 70. The recesses 72 can communicate and / or extend the clearances 44, so that the elastic means 36 are essentially empty. Each blade 70 can be thinner than the tape 34. This increases the compactness and flexibility.

The radial stiffness of the set of blades 70 can be at least: two or ten times less than the axial and / or circumferential stiffness.

FIG. 7 outlines the elastic means 36. They can comprise elastic wires 74, for example intermingled, forming a stud 42 in contact with the ribbon 34. The wires 74 can be made of metal, for example spring steel.

Recesses 72 can be made between the wires 74. The recesses 72 can communicate and / or extend the clearances 44, so that the elastic means 36 are essentially empty. Each wire 74 can be thinner than the ribbon 34.

FIG. 8 sketches the elastic means 36 which may comprise a block of elastic foam 76, in particular forming a stud 42 in contact with the tape 34. The block of foam 76 may be made of polymer. Its pores form recesses 72, and can communicate with each other, and in particular with the recesses 44.

According to the invention, the elastic means 36 may comprise a combination of elastic blades, elastic threads, foam, to form different pads; possibly of different natures. Optionally, only one type of its means, for example the block of foam, circumferentially occupies the entire associated groove; possibly without clearance.

Figure 9 is a diagram of an operating method of a

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BE2018 / 5120 turbomachine. The turbomachine and in particular the sealing system, may be identical or similar to those described in relation to Figures 1 to 8.

The process can comprise the following stages, in particular carried out in the following order:

(a) stopping 100 of the turbomachine where the rotor remains stationary relative to the stator;

(b) rotation 102 of the rotor and of the rotor vanes inside the ribbon, possibly accompanied by offsets of the rotor relative to the axis of rotation;

(c) radial contact 104 of the outer edges of the rotor blades with the ribbon, when the radial clearances close and become harmful, at least on an angular section of the ribbon.

During step (c) contact 104, the outer edges slide circumferentially against the tape, and push it radially back into the groove, compressing the elastic means. Thanks to the choice of materials, friction and abrasion are limited or harmful. With this in mind, a polymer ribbon such as kevlar, and a metal blade, for example made of titanium or aluminum, offer satisfactory results. The coefficients of friction of the blades with the ribbon and with the casing can then vary greatly.

In addition, step (c) contact 104 is carried out while keeping the radius R. at the end of step (c) contact 104 the radius R is identical to that of steps (a) stop 100 and (b ) rotation 102.

Claims (20)

1. Sealing system (36) for a turbomachine (2), in particular for a turbomachine compressor (2), the sealing system (36) comprising: - an annular row of rotor blades (24) with external edges (40); - external support; - A ribbon (34) defining radial clearances (46) against the external edges of the (40) rotor blades (24); - elastic means (38) connecting the strip (34) in an elastic manner to the external support; characterized in that perpendicular to the axis of rotation of the turbomachine (2), the outer edges (40) of the blades (24) include rounded profiles (52) which are radially opposite the ribbon (34). 2. Sealing system (36) according to claim 1, characterized in that the elastic means (38) comprise internal recesses (72). 3. Sealing system (36) according to one of claims 1 to 2, characterized in that the elastic means (38) have an axial stiffness, and a radial stiffness less than the axial stiffness. 4. Sealing system (36) according to one of claims 1 to 3, characterized in that the elastic means (38) comprise studs (42) distributed along the circumference, the number of studs (42) exceeds d ' at least 10% the number of rotor blades (24) in the annular row. 5. Sealing system (36) according to one of claims 1 to 4, characterized in that the elastic means (38) include recesses (44) distributed along the circumference, in particular distributed between the studs (42). 6. Sealing system (36) according to one of claims 1 to 5, characterized in that the elastic means (38) comprise sets of elastic blades (70). 2018/5120 BE2018 / 5120 7. Sealing system (36) according to claim 6, characterized in that the elastic blades (70) of each set intersect. 8. Sealing system (36) according to one of claims 1 to 7, characterized in that the elastic means (38) comprise blocks of polymer foam (76). 9. Sealing system (36) according to one of claims 1 to 8, characterized in that the elastic means (38) comprise elastic threads (74). 10. Sealing system (36) according to one of claims 1 to 9, characterized in that each radial clearance (46) has a radial height (H) which varies according to the circumference of the same rounded profile (52) associated. 11. Sealing system (36) according to one of claims 1 to 10, characterized in that the support comprises a sealed annular groove (32) in which the tape (34) and the elastic means (38) are completely housed . 12. Sealing system (36) according to one of claims 1 to 11, characterized in that the coefficient of friction between the outer edges (40) of blades (24) and the ribbon (34) is less than the coefficient of friction between the outer edges of the blades and the support, and / or less than the coefficient of friction between the outer edges (40) of the blades (24) and the elastic means (38), the ribbon (34) comprises or is an anti-friction coating. 13. Sealing system (36) according to one of claims 1 to 12, characterized in that the tape (34) is made of polymeric material. 14. Sealing system (36) according to one of claims 1 to 13, characterized in that the tape (34) is made of kevlar. 15. Sealing system (36) according to one of claims 1 to 14, characterized in that the tape (34) is segmented along its circumference (54). 2018/5120 BE2018 / 5120 16. Sealing system (36) according to one of claims 1 to 15, characterized in that the elastic means (38) comprise piezoelectric sensors (78), and the system (36) comprises a detection module (80 ) deformation of the ribbon (34). 17. Sealing system (36) according to one of claims 1 to 16, characterized in that the thickness of the strip (34) is less than the average thickness of the rotor blades (24), in particular the average thickness external edges (40). 18. Turbomachine (2), in particular an aircraft turbojet engine capable of ingesting a volatile, the turbomachine (2) comprising a sealing system (36), characterized in that the sealing system conforms to one of the Claims 1 to 17, preferably the compressor is a low-pressure compressor (4). 19. Method of operating a turbomachine (2) with a sealing system (36), the sealing system (36) comprising: - an annular row of rotor blades (24) with external edges (40); - external support; - a ribbon (34) defining radial clearances (46) with the outer edges (40); - elastic means (38) connecting the strip (34) in an elastic manner to the external support; the process comprising the following steps: (b) rotation (102) of the rotor blades inside the ribbon (34); (c) radial contact (104) of the outer edges (40) of the rotor blades (24) with the ribbon; characterized in that, depending on the thickness of the blades, in particular along the circumference, the outer edges (40) of the blades (24) comprise rounded profiles (52) of radius R and radially facing the ribbon (34); 2018/5120 BE2018 / 5120 and in that during step (c) contact (104) the or each radius R remains constant, the system (36) possibly being in accordance with one of claims 1 to 17. 20. The method of claim 19, characterized in that during step (c) 5 contact (104), the edges (40) of blades (24) touch a contact area of the ribbon (34), and in that during step (c) contact the thickness of the tape in the contact area remains constant.