Sealing gasket for an aircraft turbomachine

Abstract

The invention relates to a sealing gasket for an aircraft turbomachine comprising a plurality of sealing gasket sectors (20) distributed circumferentially around a longitudinal axis (X), each sealing gasket sector (20) comprising a radially inner annular wall sector (22) and a radially outer annular wall sector (24) connected to one another by an elastically deformable member (26), wherein each radially inner annular wall sector (22) is connected to an inner radial tab (28) and each radially outer annular wall sector (24) is connected to an outer radial tab (24), the inner tab (28) and the outer tab (30) being connected to one another by the elastically deformable member (26) which is formed of a stack of a plurality of contiguous elastic strips (32).

Description

Description Title: Seal for an aircraft turbomachine Technical field

[0001] The present disclosure relates to an annular seal, such as a hydrostatic annular seal. The present document also relates to an assembly comprising such a seal as well as a turbine or a turbomachine comprising such a seal. Prior art

[0002] Figure 1 schematically represents a turbomachine 1 with a double flow of longitudinal axis X. The turbomachine 1 generally comprises, from upstream AM to downstream AV according to the direction of flow of the gases within the turbomachine 1, a fan 2, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6, a low-pressure turbine 7 and an exhaust system downstream of the turbomachine 1. The gas flow, in particular air, entering upstream of the turbomachine 1 first circulates through the fan 2 then divides, on the one hand, into an annular circulation vein called the primary vein 8, and on the other hand, into an annular circulation vein called the secondary vein 9 surrounding the primary vein 8. The low-pressure compressor 3, the high-pressure compressor 4, the combustion chamber 5, the high-pressure turbine 6 and the low-pressure turbine 7 are arranged in the primary vein 8.

[0003] In this document, the terms "longitudinal", "radial" and "circumferential" are defined with respect to the longitudinal axis X of the turbomachine 1, the longitudinal axis X being the same as the axis of rotation of the low-pressure and high-pressure rotors of the turbomachine 1. The terms "inner" and "outer", as well as "internal" and "external", are then defined in the radial direction with respect to the longitudinal axis X. The terms, upstream and downstream are defined with respect to the general direction of flow of the gases in the turbomachine along the longitudinal axis X around which the turbomachine extends.

[0004] Reference is now made to Figure 2A schematically representing a partial view of a low-pressure turbine 7 with a longitudinal axis which comprises an alternation of annular rows of moving blades 9 arranged longitudinally in alternation with annular rows of stator blades 10. In Figure 2, only two annular rows of rotor blades 9 and one annular row of stator blades 10 are shown. The annular rows of rotor blades 9 or moving blades 9 are connected to each other by a cylindrical shell 1 1 .

[0005] Each of the annular rows of stator blades 10 comprises a radially inner annular platform 12 and a radially outer annular platform (not shown) between which a plurality of blades 13 extend. The radially outer annular platform is fixed to a casing of the turbine.

[0006] Managing the seal between the end of the stator blades 10 and the shell 11 of the rotor is important to limit gas leaks between the rotor and the stator 10 and to control the pressure and temperature conditions on either side of said seal and also below the seal. For this purpose, it is known to provide a radial annular partition 14 extending from said radially internal annular platform inwards, and carrying at one end the sealing member 15 intended to maintain in operation a small clearance with the corresponding shell of the rotor so as to limit the passage of air through the seal 15 in operation. With reference to FIG. 2C, the hydrostatic annular seal 15 preferably comprises a ring 15a extending radially outwards from the radially external annular wall 24.For example, the ring 15a may have a U-shaped section, formed of two branches spaced longitudinally from one another and between which the radial partition 14 is arranged. The two branches of the U-shaped ring and the radial partition 14 may be positioned relative to one another via centering pins.

[0007] To this end and as shown in Figures 2A and 2B, the annular row of stator blades 10 carries an annular clearance control seal 15 arranged radially inside the annular row of stator blades 10 and radially outside the cylindrical shell 11, the annular clearance control seal 22 cooperating in a contactless seal with the cylindrical shell 11 in order to limit the circulation from upstream of the annular row of stator blades 10 to downstream in the annular space between the seal 15 and the cylindrical shell 11.

[0008] In particular, such a clearance control seal 15 operates with a low and controlled annular clearance between the latter and the shell 11 when the turbine is in operation. Furthermore, this type of seal aims to achieve an adaptation of the clearance in operation. The use of the hydrostatic seal 15 then offers the advantage of limiting the leakage flow at the level of the seal, and thus makes it possible to improve the performance of the turbomachine and to reduce the requirements in terms of thermal and mechanical stresses when sizing the various components of the turbine 7.

[0009] As shown in Figure 2B, the hydrostatic annular seal 15 may be formed of two concentric annular walls 16, 17, and a plurality of elastically deformable members arranged circumferentially next to each other and extending between the two walls 16, 17 and including in particular elastically deformable blades 18 extending circumferentially. For example, document WO 2009 / 148787 describes such a seal. This configuration makes it possible to improve the control of the radial deformation of the seal 15, and therefore the control of the clearance between the seal 15 and the shell 11 cooperating with the sealing seal 15 so as to limit the passage of air.

[0010] This document aims to provide a simple, reliable and economical solution to this need. Summary

[0011] The present document relates to a seal for an aircraft turbomachine comprising a plurality of seal sectors distributed circumferentially around a longitudinal axis, each seal sector comprising a radially inner annular wall sector and a radially outer annular wall sector connected to each other by an elastically deformable member, in which each radially inner annular wall sector is connected to an inner radial tab and each radially outer annular wall sector is connected to an outer radial tab, the inner and outer tabs being connected to each other by the elastically deformable member which is formed of a stack of a plurality of contiguous elastic strips.

[0012] The formation of an elastically deformable member with contiguous lamellae makes it possible to connect the radially inner annular wall sector to the radially outer annular wall sector. Thus, the radially inner annular wall sector can move radially by deforming by bending of the elastically deformable member in a controlled manner via its radial stiffness, while being robust to torsion and axial forces generated by the pressure difference between the upstream and downstream of the seal when the latter is arranged opposite a rotating cylindrical shell.

[0013] The elastic jointing lamellas can be removed from the internal and external legs, which makes it easy to replace a faulty seal sector directly during maintenance operations. In fact, it is possible to remove only the jointing lamellas or the jointing lamellas and a radially internal wall sector, without having to change the entire annular seal, which reduces the cost of using this type of seal.

[0014] Adjusting the radial stiffness of the seal is done simply by changing the number and thickness of the lamellae, which can be done analytically.

[0015] This seal architecture allows working at low stiffnesses without having to face manufacturing issues such as the minimum thickness that can be produced by conventional machining (milling, turning, etc.) or by special processes (EDM, etc.). Indeed, the lamellae can be obtained from a supply of rolled plates whose manufacturing process offers precise control of the thickness dimension.

[0016] Furthermore, non-compliant seal areas are avoided because the seal stiffness is not achieved through any machining that could result in out-of-tolerance parts. In this system, the radial stiffness of the seal is directly related to the stacking of the lamellae. However, the thickness and tolerance interval of the lamellae is known before assembly. It is therefore possible to choose the combination of lamella thicknesses to be assembled to achieve the targeted stiffness.

[0017] Another effect created by the stacking of the lamellae is the creation of differential microdisplacements between a lamella and its radial neighbor(s), when all of them are subjected to bending (tension-compression). This comes from the fact that the overall deformation is that of a beam in bending, but, within each of the sheets taken individually, the free edges at the interface undergo opposing stresses: traction on one side, compression on the other. Differential displacements occur both in the case of a static deformation and in the case of a modal deformation. Consequently, the architecture allows the lamellae to rub against each other, thus creating damping by energy dissipation. This damping makes it possible to improve the dynamic behavior of the seal, by limiting the amplitude of the modal deformations.

[0018] Finally, the solution is radially compact, which facilitates the integration of the seal into its environment.

[0019] According to another characteristic, at least one of the internal radial tab and the external tab comprises a notch in which a circumferential end of each of the strips is longitudinally engaged, said strips being held radially in said notch.

[0020] According to another characteristic, each of the internal and external radial legs comprises a notch in which a circumferential end of each of the strips is longitudinally engaged, said strips being held radially in said notch.

[0021] According to another characteristic, the internal radial tab of a seal sector comprises a circumferentially traversing recess in which a circumferential end of each of the strips is engaged, a locking member passing through the thickness of the strips so as to fix the strips to the radially internal annular wall sector.

[0022] In a particular embodiment, the locking member may be a pin passing through the radially internal annular wall sector and the internal radial lug.

[0023] According to another characteristic, the circumferential dimension of the lamellas may be greater than the thickness dimension and the longitudinal dimension of the lamellas so that the lamellas exhibit mechanical deformation behavior similar to that of a beam.

[0024] According to another feature, the slats can be fixed to each other and to the inner and outer radial legs at their circumferential ends.

[0025] The slats are thus devoid of attachment between their circumferential ends for attachment to the internal and external radial legs.

[0026] The absence of a connection between the slats between their circumferential ends allows for greater flexibility than with a single blade having the same thickness as the sum of the thickness of all the slats.

[0027] According to another characteristic, the elastically deformable member comprises between 2 and 40, preferably between 2 and 30 stacked lamellae.

[0028] According to another characteristic, each lamella may comprise a thickness of between 0.05 and 5 mm and a width in the longitudinal direction of between 5 and 50 mm.

[0029] According to another feature, the lamellae may be metallic, the lamellae being welded to the radial tabs at their circumferential ends.

[0030] According to another feature, According to another feature, the radially outer annular wall sectors may form a monolithic annular wall, the radially inner annular wall sectors being arranged circumferentially end to end.

[0031] This document also relates to a turbine for a turbomachine, for example an aircraft turbine, the turbine comprising a rotor and a casing, a distributor mounted in the casing, the distributor carrying a seal as described above and the rotor comprising a cylindrical shroud driven in rotation about the longitudinal axis and the cylindrical shroud being arranged radially under the distributor.

[0032] This document also relates to a turbomachine comprising a seal or a turbine as described above. Brief description of the drawings

[0033] [Fig. 1] schematically illustrates a sectional view of an example of a turbomachine;

[0034] [Fig. 2] schematically illustrates a partial view of a part of a turbine, for example low pressure, Figure 2B being an enlargement of the seal illustrated in Figure 2A;

[0035] [Fig. 2C] similar to Fig. 2A illustrates a method of connecting the seal to the stator;

[0036] [Fig. 3] illustrates a schematic sectional view of a sector of a jointed lamella seal according to this document;

[0037] [Fig. 4] illustrates a schematic view of a radial leg according to a variant;

[0038] [Fig. 5] illustrates three different embodiments A, B and C of sealing strips intended to form the elastically deformable member of the sealing joint according to this document;

[0039] [Fig. 6] illustrates a variant of the connection of the adjoining lamellae;

[0040] [Fig. 7] illustrates four different embodiments of a strip for a seal according to this document. Description of the embodiments

[0041] Reference is made to Figure 3A which represents a seal 19 for a turbomachine, for example an aircraft, comprising a plurality of seal sectors 20 distributed circumferentially around a longitudinal axis X. Each seal sector 20 comprises a radially inner annular wall sector 22 and a radially outer annular wall sector 24 connected to each other by an elastically deformable member 26, in which each radially inner annular wall sector 22 is connected to an inner radial tab 28 and each radially outer annular wall sector 24 is connected to an outer radial tab 30, the inner 28 and outer 30 tabs being connected to each other by the elastically deformable member 26 formed of a stack of a plurality of adjoining elastic strips. The outer annular wall is here monolithic but could also be formed of a plurality of sectors.

[0042] The inner leg 28 extends radially outward from the radially inner annular wall sector 22 and the outer leg 24 extends radially inward. from the radially outer annular wall sector 24. The radially outer end of the inner radial tab 28 is arranged at a distance from the radially outer annular wall sector 24. The radially inner end of the outer radial tab 30 is arranged at a distance from the radially inner annular wall sector 22. In operation, the radially inner wall sector 22 and the inner radial tab 28 move radially due to the bending of the elastically deformable member.

[0043] As shown in Figure 3B, the elastically deformable member 26 thus comprises a stack of a plurality of contiguous lamellae 32. The lamellae are in contact with each other but are only fixed to each other at their connecting ends to the internal radial tab 28 and external radial tab 30. The adjustment of the radial stiffness of each joint sector can be carried out very simply by modifying the number and thickness of the lamellae and is analytically calculable. The lamellae can be sheets whose dimensional characteristics can be as determined below.

[0044] The circumferential dimension of the lamellae is sufficiently large compared to the radial dimension and the longitudinal dimension so that the lamellae provide a flexural beam function. The length to width ratio is preferably greater than 2 and / or the length to thickness ratio is greater than 10.

[0045] The stiffness of the flexible arm can be calculated analytically using the following formula:

[0047] With E the Young's modulus of the single material constituting the blades (MPa), l the blade width (mm), e the blade thickness (mm), N the number of blades and L the blade length (mm).

[0048] The stacking of the lamellae 32 creates differential micro-displacements between a lamella 32 and its radially neighbor(s), when all of them are subjected to bending (tension compression). This comes from the fact that the overall deformation is indeed that of a beam in bending, but, within each of the sheets taken individually, the free edges at the interface undergo opposing stresses: traction on one side, compression on the other. The differential displacements occur both in the case of a static deformation and in the case of a modal deformation. Consequently, the architecture allows the lamellae to rub against each other, thus creating damping by energy dissipation. This damping makes it possible to improve the dynamic behavior of the joint, by limiting the amplitude of the modal deformations.

[0049] The slats 32 are fixed to each other and to the inner 28 and outer 30 radial tabs at their circumferential ends. Thus, the slats are devoid of fixing apart from their said circumferential ends and are simply joined.

[0050] In one embodiment, the lamellae 32 are formed by metal lamellae, for example made of steel, titanium, aluminum alloy, cobalt-based alloy, nickel-based alloy, the lamellae may be welded to the radial tabs at their circumferential ends. Each lamella may have a thickness of between 0.05 and 5 mm and a width in the longitudinal direction of between 5 and 50 mm. The elastically deformable member may comprise between 2 and 40, preferably between 2 and 30 lamellae.

[0051] At least one of the inner radial lug 28 and the outer lug 30 may comprise a notch 34 in which the circumferential ends of the blades 32 are longitudinally engaged, said blades 32 being retained radially in said notch 34. In Figure 4, the notch 34 is illustrated on the inner radial lug 28. The same notch may be formed on the outer radial lug 30. Furthermore, in the event of failure of an annular seal 26, the blade block 32 may be easily removed and replaced, which limits the intervention time and the parts to be changed. The notches 34 may open longitudinally to allow the blades to be mounted (Figure 4A). An axial locking plate may be arranged on the face of the inner radial wall 28 and / or outer 30 at which the notch 34 opens.The notch 34 may be closed at its opening end, that is to say at its upstream end, by a sheet 29 fixed on the upstream face of the internal radial lug 28. This sheet 29 may be fixed by welding or brazing. In another embodiment illustrated in FIG. 4B, the notch 34 may not be opening longitudinally.

[0052] In another embodiment of the invention, the internal radial tab 28 of a seal sector may comprise a recess 36 or circumferentially passing through orifice in which circumferential ends of lamellae 32 are engaged, a locking member 38 longitudinally and circumferentially locking the lamellae 32 between the radially internal annular wall sectors 22 (figure 6). In practice, the lamellae 32 may extend circumferentially on either side of the internal radial tab 28 and are locked on this tab 28 by the member 38. The locking member 38 may be a rod inserted into a bore in the internal radial tab 28 and into orifices in the lamellae 32.

[0053] Figure 5 shows several ways of connecting the slats to the legs. Figure 5 thus illustrates three types of slats 32a, 32b, 32c. The slat 32a has a shape rectangular and includes two holes 40 at its ends. The strip 32b has a rectangular shape and includes two ears or protrusions 42 each having a hole 40, the protrusions are formed at the circumferential ends of the strip 32b. The strip 32c has a rectangular shape and is identical to the strip 32b except that it is devoid of holes in the ears or protrusions.

[0054] Figure 7 illustrates four embodiments of a rectangular-shaped strip 44a, 44b, 44c, 44d. In each of the embodiments, the strips are hollowed out, which makes it possible, as required, to reduce the surface area in contact with the sheets, reduce the total weight of the elastically deformable member, and adjust the stiffness in the different directions of the elastically deformable member.

[0055] The lamella 44a comprises a substantially rectangular central recess and two portions 46 connecting the vertices of the rectangle. The lamella 44b comprises two portions 48 connecting the largest edges of the rectangular shape of the lamella 44b. The two portions 48 are substantially perpendicular to said largest edges. These two portions 48 may also be inclined as in the lamella 44c and not necessarily parallel to each other. The lamella 44d comprises a central recess 50 of elliptical shape. The recess may also be of any other shape (circular, rectangular, trapezoidal, etc.).

Claims

Claims

1. A seal for an aircraft turbomachine comprising a plurality of seal sectors (20) distributed circumferentially around a longitudinal axis (X), each seal sector (20) comprising a radially inner annular wall sector (22) and a radially outer annular wall sector (24) connected to each other by an elastically deformable member (26), in which each radially inner annular wall sector (22) is connected to an inner radial tab (28) and each radially outer annular wall sector (24) is connected to an outer radial tab (24), the inner (28) and outer (30) tabs being connected to each other by the elastically deformable member (26) which is formed of a stack of a plurality of contiguous elastic strips (32).

2. A seal according to the preceding claim, wherein at least one of the internal radial tab (28) and the external tab (30) comprises a notch (34) in which a circumferential end of each of the strips (32) is longitudinally engaged, said strips (32) being held radially in said notch (34).

3. Seal according to the preceding claim, in which each of the internal (28) and external (30) radial tabs comprises a notch (34) in which a circumferential end of each of the strips (32) is longitudinally engaged, said strips (32) being held radially in said notch (34).

4. A seal according to claim 1 or 2, wherein the internal radial tab (28) of a seal sector comprises a circumferentially traversing recess (36) in which a circumferential end of each of the strips (32) is engaged, a locking member (38) traversing the thickness of the strips (32) so as to fix the strips (32) to the radially internal annular wall sector (22).

5. A seal according to the preceding claim, wherein the circumferential dimension of the slats (32) is greater than the thickness dimension and the longitudinal dimension of the slats (32) so that the slats (32) exhibit mechanical deformation behavior similar to that of a beam.

6. A seal according to any preceding claim, wherein the slats (32) are secured to each other and to the inner (28) and outer (30) radial tabs at their circumferential ends.

7. Seal according to one of the preceding claims, in which it comprises between 2 and 40, preferably between 2 and 30 stacked lamellae (32).

8. A seal according to any preceding claim, wherein each strip (32) has a thickness of between 0.05 and 5 mm and a width in the longitudinal direction of between 5 and 50 mm.

9. A seal according to any preceding claim, wherein the strips (32) are metallic, the strips (32) being welded to the radial tabs at their circumferential ends.

10. A seal according to any preceding claim, wherein the radially outer annular wall sectors (24) form a monolithic annular wall, the radially inner annular wall sectors (22) being arranged circumferentially end to end.

11. Turbine for a turbomachine, for example an aircraft turbine, the turbine comprising a rotor and a casing, a distributor (10) mounted in the casing, the distributor (10) carrying a seal according to any one of the preceding claims and the rotor comprising a cylindrical shell (11) driven in rotation about the longitudinal axis (X) and the cylindrical shell (11) being arranged radially under the distributor (10).

12. Turbomachine (1) comprising a seal according to one of claims 1 to 10 or a turbine according to the preceding claim.

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