Moving turbine blade of a turbomachine comprising a sandwich structure

Abstract

The invention relates to a movable turbine blade (1) of a turbomachine, comprising a foot (2) configured to be mounted on a rotor disk, a blade (3) extending radially from the foot (2), and a tail (4) located at the top of the blade (3), the tail (4) comprising a platform (6) carrying at least one blade (7, 8) which projects radially from the platform (6), characterized in that the platform (6) comprises a sandwich structure (15) including a core (15c) made of a cellular material, an outer wall (15a) and an inner wall (15b) located radially on either side of the core (15c). Figure 4

Description

Title of the invention: Movable turbine blade for a turbomachine comprising a sandwich structure. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the general field of turbomachinery, and more specifically to the field of moving turbine blades, in particular moving turbine blades. In particular, it concerns the technical field of moving blades with a heel.

[0002] The invention applies to all types of land or aeronautical turbomachinery, and in particular to aircraft turbomachinery such as turbojets and turboprops.

[0003] The invention thus proposes a turbomachine blade comprising a sandwich structure, a turbine comprising such a blade, and a turbomachine comprising such a turbine. STATE OF THE ART

[0004] A turbomachine, for example a turbofan engine, typically includes an air inlet sleeve through which air is drawn into a fan before being split into a central primary flow and a secondary flow surrounding the primary flow.

[0005] The primary flow circulates in a space called the primary stream, delimited by a rotor and an internal rotating structure of the engine surrounding this rotor, and it passes through rotating elements comprising bladed wheels carried by the rotor and fixed elements such as rectifiers and distributors. The internal structure is delimited by housings comprising a low- and high-pressure compressor housing, a primary stream housing, a low- and high-pressure turbine housing, and an exhaust housing.

[0006] The secondary flow circulates in a space called the secondary channel which extends radially between the internal structure and an external structure called the hull or nacelle, which surrounds the internal structure. After being set in motion by the fan and passing through fixed blades, this secondary flow is propelled downstream to generate thrust, it being understood that the terms upstream and downstream are to be considered with respect to a principal normal gas flow direction, from upstream to downstream, for a turbomachine.

[0007] After passing through the blower, the primary flow passes through a high-pressure compressor, a combustion chamber and then high-pressure and low-pressure turbines to drive the blower, before being propelled out of the engine.

[0008] Such a turbine comprises stages, each including a series of blades carried by a corresponding rotor disk and surrounded by a portion of a housing. Sealing is ensured by a labyrinth seal comprising an abradable material carried by the housing, and flaps extending from the radial end of each blade to cooperate with the abradable material. Each flap can cooperate by contact or by being positioned with a small gap relative to the abradable material to limit air circulation between the flaps and the abradable material.

[0009] As can be seen in figures 1 to 3, such a blade 1 comprises a foot 2 by which it is mounted on the disk which carries it, a blade 3 extending the foot 2 in a radial direction called span EV, and a heel 4 at a radial end of the blade 3.

[0010] The heel 4 comprises a platform 6 extending in a direction normal to the direction EV, which carries several slats, here for example two slats 7 and 8, spaced apart along the axis of rotation AX of the motor. The platform 6 thus forms an inter-slat zone. It is extended upstream beyond slat 7, with an upstream spur 11, and downstream beyond slat 8, with a downstream spur 12. In addition, the platform 6 comprises circumferentially opposite portions, or circumferential end edges, on the circumferential periphery of the platform 6 connecting its upstream and downstream portions. Each of the circumferential end edges of the platform 6 has, between the blades 7 and 8, a profile substantially in a “Z” shape, but in the case of other blades, this profile may take the form of a “U” or a “V”, for example.

[0011] In order to dampen the vibrations to which the blades 1 are subjected during operation and to provide rigidity to the assembly, the blades 1 are mounted on their disk with a torsional stress around their stacking axis EV. The geometry of the flanges 4 is such that each blade 1 is subjected to torsional stress by bearing on the circumferentially adjacent blades 1 at the circumferential end edges, which thus define inter-blade contact surfaces and are the site of significant friction during the operation of the turbomachine. To protect against wear, these circumferential end edges are provided with a coating 13, 14, visible in [Fig. 2], made of a wear-resistant, friction-resistant material. This could, for example, be a material marketed under the Stellite® brand.

[0012] In the context of the design of moving turbine blades for turbomachinery, in particular moving blades for low pressure turbines, one of the main challenges is the design of the area concerned by the heel at the top of the blade.

[0013] Indeed, the proper distribution of the centrifugal force, and the resulting stresses, depends in particular on balancing the mass of the heel relative to the rest of the part, as well as control of the stiffness of the heel area in order to limit local deformations of the heel as much as possible.

[0014] One of the goals of this design phase is therefore to seek to minimize the mass of the heel, while ensuring sufficient stiffness to limit the adverse effects of this mass once it is rotated, all while respecting certain specific requirements of the heel area.

[0015] More specifically, there is a need for the design of the heel platform, located between the toe pieces and which generally contains the dynamic damping function. These are relatively thin areas, therefore inherently not very stiff, and which contribute cantilevered mass.

[0016] In existing solutions, such as the one shown in [Fig.1] described above, the envisaged morphologies do not guarantee sufficient stiffness of the heel for a reduced weight, which limits the stresses to which the heel can be subjected in operation.

[0017] By way of example, French patent applications FR 2 955 608 Al, FR 2 970 999 Al, FR 3 079 848 Al and FR 3 079 929 Al describe examples of turbine blade heel design for turbomachinery.

[0018] However, for certain turbomachine configurations, centrifugal forces can increase significantly depending on the chosen architecture, which can lead to a substantial increase in rotational speed. This results in an increased mass of the heel to achieve sufficient strength. The deformations of the heel on an operating blade are then significant at the tips, particularly at the blade tips, and are related to the fact that the cantilevered masses are driven by the centrifugal force and subsequently overstress the area radially below the opposite heel.

[0019] Studies have been able to confirm that increasing the stiffness of the heel, particularly at the platform level, has a strong impact on reducing radial stresses under the heel, and all the more so when the centrifugal force is significant.

[0020] There is therefore also a need to improve the mechanical resistance in the heel area of ​​a turbomachine blade, by reducing the mass while maintaining sufficient local stiffness for the blade. Description of the invention

[0021] The invention aims to remedy at least partially the needs mentioned above and the disadvantages relating to the achievements of the prior art.

[0022] The invention thus relates, according to one of its aspects, to a movable turbomachine blade intended to be mounted around an axis, comprising a foot configured to be mounted in a recess which opens at the outer periphery of a disk of rotor centered on the axis, a blade extending radially from the axis from the root in a radial span direction, and a heel located at the top of the blade, the heel comprising a platform carrying at least one blade extending radially in projection from the platform,

[0023] characterized in that the platform comprises a sandwich structure including a core made of a cellular material, an outer wall and an inner wall, the inner and outer walls being located radially on either side of the core.

[0024] Thanks to the invention, it is possible to improve the mechanical resistance in the root zone of a turbomachine blade, while respecting the usual criteria, by reducing the stresses generated by the centrifugal force during operation (reduction of root deformation following the increase in local stiffness). The addition of the sandwich structure makes it possible to increase the stiffness while minimizing the added mass.

[0025] The turbomachine blade according to the invention may further comprise one or more of the following characteristics taken individually or in any possible technical combinations.

[0026] The blade may be a movable turbine blade, in particular a movable low-pressure turbine blade.

[0027] The external and internal walls may have a rigidity greater than that of the core.

[0028] The outer and inner walls can be in contact with the core.

[0029] An external surface of the inner wall may extend over the entire internal surface of the core, particularly in contact with the inner surface of the core. Furthermore, an internal surface of the outer wall may extend over the entire external surface of the core, particularly in contact with the outer surface of the core.

[0030] The platform can carry an upstream and a downstream slat. The platform can be extended upstream by an upstream spoiler projecting from the upstream slat and downstream by a downstream spoiler projecting from the downstream slat. The sandwich structure can be mounted on the platform and positioned between the upstream and downstream slats. The sandwich structure can preferably be mounted in contact with the upstream and downstream slats, in particular via axial surface contact.

[0031] Furthermore, the sandwich structure can completely cover the inter-slat area of ​​the platform located between the upstream and downstream slats. Alternatively, the sandwich structure can partially cover the inter-slat area of ​​the platform that extends axially between the upstream and downstream slats. In particular, the sandwich structure may not cover a wear-resistant material coating present on at least one circumferential end edge of the platform.

[0032] The core may comprise a cellular material in the form of a metallic honeycomb, the cellular material preferably having a nickel-based composition.

[0033] The thickness of the sandwich structure can be greater than 1 mm.

[0034] In addition, the thickness of the sandwich structure can be scalable, particularly circumferentially, being in particular maximum at the center of the platform and minimum at the lateral faces of the platform.

[0035] Furthermore, the thickness of the internal and external walls can be greater than 0.4 mm and less than 1 mm.

[0036] The core may have a thickness of between 0.05 mm and 0.1 mm, for example on the order of 0.08 mm. The core may have a mesh size, or even a larger dimension of the alveoli of the cellular material of the core, of between 0.50 mm and 3.50 mm, for example on the order of 1.57 mm.

[0037] The sandwich structure can be brazed onto the blade heel platform or produced by additive manufacturing on the blade heel platform. This makes it possible to obtain different geometries and / or mesh dimensions.

[0038] Furthermore, the invention also relates, according to another of its aspects, to a turbomachine turbine, in particular a low pressure turbine, characterized in that it comprises at least one blade such as that defined above.

[0039] Furthermore, the invention also relates, according to another of its aspects, to a turbomachine comprising a blade as defined above or a turbine as defined above. BRIEF DESCRIPTION OF THE FIGURES

[0040] Other advantages, purposes and special features of the invention will become apparent from the following non-limiting description of at least one embodiment of the present invention, with reference to the accompanying figures, in which: • Figure [1] schematically represents, in perspective, an example of a known low-pressure turbine blade, • [Fig.2] is a partial schematic side view along a circumferential axis of a low-pressure turbine blade similar to that of [Fig.1], • [Fig.3] is a partial schematic view of the top of a low-pressure turbine blade similar to that of [Fig.1], • Figure 4 schematically and partially illustrates, from a side view, a low-pressure turbine blade according to the invention, and • [Fig.5] illustrates, schematically in partial section, the sandwich structure of the blade of [Fig.4].

[0041] Throughout these figures, identical references may designate identical or analogous elements.

[0042] Furthermore, the different parts shown in the figures are not necessarily to a uniform scale, in order to make the figures more legible. DETAILED DESCRIPTION OF THE INVENTION

[0043] Figures 1 to 3 have already been described previously in the section relating to the prior art and the technical background of the invention.

[0044] Throughout this description, given by way of non-limiting example, it is noted that the terms upstream and downstream are to be considered with respect to a principal direction F of normal gas flow (from upstream to downstream) for a turbomachine. Furthermore, the radial axis of symmetry of the turbomachine is called the AX axis of the turbomachine. The axial direction of the turbomachine corresponds to the rotation axis AX of the turbomachine. A radial direction of the turbomachine is a direction perpendicular to the AX axis of the turbomachine.

[0045] Furthermore, unless otherwise specified, the adjectives and adverbs axial, radial, axially, and radially are used with reference to the aforementioned axial and radial directions. In addition, unless otherwise specified, the terms inside and outside are used with reference to a radial direction such that the inside of an element is closer to the AX axis of the turbomachine than the outside of the same element.

[0046] With reference to [Fig.4], a low-pressure turbine blade 1 according to the invention has been schematically represented in cross-section along the axis of rotation AX.

[0047] The blade 1 thus comprises a foot 2 which allows its mounting in a cavity opening at the outer periphery of a rotor disk centered on the axis AX, a blade 3 extending radially with respect to the axis AX from the foot 2 in the radial direction of span EV, and a heel 4 located at the top of the blade 3.

[0048] The heel 4 comprises a platform 6 carrying an upstream flap 7 and a downstream flap 8 which extend radially in projection from the platform 6. The platform 6 is extended, upstream, by an upstream spoiler 11 extending in projection from the upstream flap 7 and, downstream, by a downstream spoiler 12 extending in projection from the downstream flap 8 in upstream and downstream directions relative to the normal flow direction F of the gases in the turbomachine.

[0049] In order to maximize the stiffness of the blade 1 while limiting the added mass, the platform 6 comprises a sandwich structure 15 including a core 15c made of a cellular material and two walls, or skins, external 15a and internal 15b, located radially on either side of the core 15c. The walls 15a, 15b are rigid, exhibiting greater stiffness than the core 15c, which is made of a lightweight material. Advantageously, the external surface of the internal wall 15b extends over the entire surface internal of the core 15c, and the internal surface of the external wall 15a extends over the entire external surface of the core 15c.

[0050] As seen in [Fig.4], the sandwich structure 15 is mounted on the platform 6 and positioned between the upstream slat 7 and the downstream slat 8, being mounted in axial surface contact with the upstream slats 7 and downstream 8.

[0051] The sandwich structure 15 can completely cover the inter-slat area of ​​the platform 6, which extends axially between the upstream slats 7 and downstream slats 8. Alternatively, it can only partially cover this inter-slat area of ​​the platform 6, in particular to avoid covering the wear-resistant material coatings 13, 14, usually the material marketed under the Stellite® brand, as described above. Conventionally, this wear-resistant material is deposited on the circumferential end edges by welding, for example by drop welding, which involves creating an electric arc to melt the material. The Stellite® alloy is a steel alloy with a high chromium (Cr) and cobalt (Co) content. It may also contain a small amount of tungsten (W) or molybdenum (Mo) and a small amount of carbon (C).

[0052] The core 15c and the walls 15a, 15b of the sandwich structure 15, more clearly visible in [Fig. 5], may be metallic, in particular nickel. The core 15c is in particular a cellular material in the form of a metallic honeycomb, but any other pattern is also possible within the scope of the invention. The core 15 can generally be designed to have sufficient stiffness for mechanical strength while maintaining a limited weight.

[0053] The sandwich structure 15 is preferably brazed onto the platform 6. However, another method for manufacturing and assembling the sandwich structure 15 onto the blade 1 could be considered, namely other than brazing, particularly if brazing would not provide sufficient mechanical strength to the area. For example, the sandwich structure 15 could be produced by additive manufacturing.

[0054] The thickness e^ of the sandwich structure 15 can vary depending on the application. In particular, it is greater than 1 mm. This thickness ei5 can be variable for certain applications. In particular, it can be maximum at the center of the platform 6 and minimum at the circumferential end faces of the platform 6, at or near the wear-resistant material coatings 13, 14 present on the circumferential end edges of the platform 6, so as to form a structure, for example, resembling a trapezoidal shape.

[0055] Furthermore, the thickness ea, eb of each wall 15a, 15b can be greater than 0.4 mm and less than 1 mm.

[0056] Furthermore, the core 15c can have a thickness ec between 0.05 mm and 0.1 mm, and a mesh size between 1.50 mm and 1.60 mm. These dimensions can vary depending on the intended applications.

[0057] Of course, the invention is not limited to the embodiments just described. Various modifications can be made to them by a person skilled in the art.

Claims

Demands

1. A movable turbine blade (1) for a turbomachine intended to be mounted about an axis (X), comprising a foot (2) configured to be mounted in a recess opening at the outer periphery of a rotor disk centered on the axis (X), a blade (3) extending radially from the axis (X) from the foot (2) in a radial span direction (EV), and a tail (4) located at the top of the blade (3), the tail (4) comprising a platform (6) carrying at least one blade (7, 8) extending radially in projection from the platform (6), characterized in that the platform (6) comprises a sandwich structure (15) comprising a web (15c) made of a cellular material, an outer wall (15a) and an inner wall (15b), the inner (15a) and outer (15b) walls being located radially on either side of the web (15c).

2. Blade according to claim 1, wherein an external surface of the inner wall (15b) extends over the entire internal surface of the core (15c).

3. Blade according to claim 1 or 2, wherein an internal surface of the outer wall (15a) extends over the entire external surface of the core (15c).

4. Blade (1) according to any one of the preceding claims, wherein the platform (6) carries an upstream slat (7) and a downstream slat (8), the platform (6) being extended, upstream, by an upstream beak (11) which projects out of the upstream slat (7) and, downstream, by a downstream beak (12) which projects out of the downstream slat (8), the sandwich structure (15) being mounted on the platform (6) and being disposed between the upstream slat (7) and the downstream slat (8), the sandwich structure (15) preferably being mounted in contact with the upstream (7) and downstream (8) slats.

5. Blade (1) according to any one of the preceding claims, wherein the sandwich structure (15) partially covers the inter-slat area of ​​the platform (6) which extends axially between the upstream (7) and downstream (8) slats, preferably the sandwich structure (15) not covering a wear-resistant material coating (13, 14) present on at least one circumferential end edge of the platform (6).

6. Blade (1) according to any one of the preceding claims, wherein the web (15c) comprises a cellular material which presents in the form of a metallic honeycomb, preferably the alveolar material having a nickel-based composition.

7. Blade (1) according to any one of the preceding claims, wherein the thickness (e^) of the sandwich structure (15) is greater than 1 mm.

8. Blade (1) according to any one of the preceding claims, wherein the thickness (ea, eb) of the external and internal walls (15a, 15b) is greater than 0.4 mm and less than 1 mm.

9. Blade (1) according to any one of the preceding claims, wherein the web (15c) has a thickness (ec) of between 0.05 mm and 0.1 mm, and a larger dimension of the alveoli of the alveolar material of the web (15c) of between 0.50 mm and 3.50 mm.

10. Blade (1) according to any one of the preceding claims, wherein the sandwich structure (15) is brazed onto the platform (6) of the heel (4) of the blade (1) or is produced by additive manufacturing on the platform (6) of the heel (4) of the blade (1).

11. Turbomachine turbine, in particular a low pressure turbine, characterized in that it comprises at least one blade (1) according to any one of the preceding claims.

12. Turbomachine, characterized in that it comprises a blade (1) according to any one of claims 1 to 10 or a turbine according to claim 11.

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