SHIM FOR A TURBOMACHINE BLADE

Abstract

A shim (20) for a turbomachine blade (14), the shim comprising two branches (20A) for coming against bearing surfaces (16A) of the blade rotor (16), and a base part (20B) interconnecting the branches. The shim presents, at least in its branches (20A), a multilayer structure having at least three layers (31, 32, 33) that are fastened to one another and superposed in the following order: a first layer (31) of a first material; a second layer (32) of a second material; and a third layer (33) of a third material that is optionally different from the first material, said first and third materials presenting respective first and third Young's moduluses of values E and E′ at any arbitrary operating temperature in the operating temperature range of the shim, and said second material presenting a second Young's modulus of value lying in the range E/20 to E/5 and in the range E′/20 to E′/5 at said operating temperature.

Description

The invention relates to shim for a turbomachine blade, the shim being of the type comprising two branches that are to come against the bearing surfaces of a blade root, together with a base part interconnecting the branches.

BACKGROUND OF THE INVENTION

The shim can be used with any type of turbomachine whether terrestrial or for aviation purposes (turbojet, turboprop, terrestrial gas turbine, etc.). In the particular circumstance of a bypass, two-spool airplane turbojet, the shim of the invention can be used for the fan blades, or for the moving blades of the low pressure compressor (or “booster”), or for the high pressure compressor, or for the high pressure turbine, or for the low pressure turbine of the turbojet.

In the present application, the axial direction corresponds to the direction of the axis A of the rotor of the turbomachine, and the radial direction is a direction perpendicular to the axis A. Furthermore, unless specified to the contrary, adjectives such as “inner” and “outer” are used relative to a radial direction in such a manner that the (radially) inner portion of an element is closer to the axis A than is the (radially) outer portion of the same element.

In a rotor disk (i.e. a disk secured to the rotor) of a turbomachine, that serves to carry blades, the (moving) blades are fastened to the disk by attachment systems, which may be constituted by shank-type fasteners that may be rectilinear or curvilinear, hammerhead-shaped, or Christmas-tree-shaped. Such fastener systems can be described as devices in which the blade roots form the male portions of the system and are held radially in the female portions of the system that are formed in the outer periphery of the disk and that are commonly known as “slots”.

When the rotor is set into rotation, the blades are subjected mainly to centrifugal forces and also to axial aerodynamic forces, and the blade roots are pressed in abutment against portions of the disk lying on either side of the outer opening of each slot, under the effect of centrifugal forces. The surfaces of the blade roots and of the disks that come into abutment against each other are commonly referred to as “bearing surfaces”. These bearing surfaces are subjected to pressure (as a result of said forces applied to said bearing surfaces). To a first approximation, it can be estimated that this pressure depends on the square of the speed of rotation of the rotor.

It can thus be understood that the variations in the speed of rotation of the rotor during an operating cycle of the turbomachine: from stationary to full throttle, passing through various particular intermediate speeds (idling, taxiing, cruising, descending, for an aviation turbomachine) give rise to variations in the pressure acting on the above-defined bearing surfaces. These pressure variations associated with elastic deformations of the contacting parts give rise to relative movements between the blade roots and the disk. When they are repeated, these relative movements, known as slip or as separation depending on their nature, give rise to wear phenomena in the bearing surfaces of the blades or of the disks. It is also possible for the dynamic movements of the blades at a given speed of rotation (response of the blades to alternating stresses of harmonic or transient nature) to contribute to the phenomenon of said bearing surfaces becoming worn. These wear phenomena are naturally penalizing on the lifetime of a turbomachine.

Various so-called “anti-wear” solutions can be adopted, i.e. solutions that slow down the appearance of wear at the contact interfaces, and these solutions include those based on inserting a third body, referred to as “shim”, between the blade roots and the disk. The shim serves in particular to double the number of contact interfaces (going from a single blade/disk interface to a pair of interfaces, blade/shim and shim/disk), and to reduce the relative movements between the parts that are in contact, thus enabling wear to be reduced in operation.

A known example of shim of the above-mentioned type is described in document FR 2 890 684. That shim is made entirely out of metal, and it is constituted by a sheet of metal that is folded appropriately.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to provide a shim that is more effective than the above-mentioned known shim in terms of performing the “anti-wear” function, so as to provide better protection to the bearing surfaces of the blades and of the disk.

This object is achieved by a shim for a turbomachine blade, the shim comprising two branches for coming against bearing surfaces of the blade rotor, and a base part interconnecting the branches, the shim being characterized in that it presents, at least in its branches, a multilayer structure having at least three layers that are fastened to one another and superposed in the following order: a first layer of a first material; a second layer of a second material; and a third layer of a third material that is optionally different from the first material, said first and third materials presenting respective first and third Young's moduluses of values E and E′ at any arbitrary operating temperature in the operating temperature range of the shim, and said second material presenting a second Young's modulus of value lying in the range E/20 to E/5 and in the range E′/20 to E′/5 at said operating temperature.

It should be noted that the Young's modulus of a material varies as a function of the temperature of the material, and consequently that the values E and E′ depend on temperature.

The term “operating temperature” is used to mean the temperature to which the shim is subjected while the turbomachine is in operation under normal conditions of use. In the present invention, the relationship between said first, second, and third Young's moduluses, as defined above, needs to be satisfied for all of the temperatures in the range of operating temperatures of the shim.

For example, when the shim belongs to the fan or to the low pressure compressor of a bypass two-spool airplane turbojet, its operating temperature lies in the range 20° C. to 150° C. When it belongs to the high pressure compressor of a bypass two-spool airplane turbojet, its operating temperature lies in the range 150° C. to 500° C. When it belongs to the high pressure turbine of a bypass two-spool airplane turbojet, its operating temperature lies in the range 400° C. to 700° C.

The present invention thus relates to adopting said multilayer structure in which the (isotropic or anisotropic) elasticity characteristics of the second material are better than the (isotropic or anisotropic) elasticity characteristics of the first and third materials in the desired operating temperature range.

In an embodiment, said first and third materials are the same or different metal alloys or organic matrix composite materials, while said second material is non-metallic. For example, and in non-exhaustive manner, the second material may be made of rubber, of silicone, of polyimide, of glass, or of epoxy resin.

The multilayer structure of the shim of the invention has the following effects:

• • uniformly distributing contact pressures by accommodation of the shim as a result of the elasticity of the second layer;
  • on a change in speed of rotation, limiting relative movements between parts due to centrifugal forces by virtue of “static” shear in the second layer; and
  • damping any dynamic movements of the blade by “dynamic” shear of the second layer.

A particular consequence of these effects is to prevent or limit wear phenomena in the bearing surfaces, thereby increasing the lifetimes of blade roots and of disks.

These effects are reinforced when the second material presents viscoelastic behavior in the operating temperature range of the shim, more particularly for the purpose of damping any dynamic movements of the blade.

The invention also provides a turbomachine rotor assembly comprising: a rotor disk presenting slots in its outer periphery; blades fastened via their roots in said slots; and shims according to the invention, each branch of each shim being disposed between the bearing surface of a blade root and the corresponding bearing surface of the disk.

Finally, the invention also provides a turbomachine including such a rotor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages can be better understood on reading the following detailed description. The description refers to the accompanying figures, in which:

FIG. 1 is a fragmentary exploded and diagrammatic view of a turbomachine rotor assembly comprising a rotor disk, an example of shim of the invention, and a blade root;

FIG. 2 is a radial section view on plane II-II showing the FIG. 1 assembly once it has been assembled;

FIG. 3 is a section view analogous to that of FIG. 2, showing another example of shim of the invention; and

FIG. 4 is a section view analogous to that of FIG. 2, showing another example of shim of the invention, placed between two adjacent slots.

MORE DETAILED DESCRIPTION

FIGS. 1 and 2 show: a rotor disk 2 having numerous grooves or “slots” 4 in its periphery that define housings, each suitable for receiving the root 16 of a blade 14, the root 16 being surrounded by a shim 20. The blade root 16 and the fan disk 2 are made out of titanium alloy, for example.

It should be observed that assemblies also exist (not shown) that have a spacer placed between the blade root 16 and the bottom of the slot 4.

When the disk 2 is set into rotation, the blades 14 are subjected to centrifugal forces, and the bearing surfaces 16A on the blade root 16 become pressed against bearing surfaces 22A of the disk 2. In the example shown, the surfaces 16A constitute the flanks of the blade root 16, while the surfaces 22A constitute the bottom faces of the lip-shaped portions 22 of the disk that extend on either side of the outer opening of each slot 4.

The shim 20 comprises two side branches 20A for coming against the bearing surfaces 16A of the blade root 16, and a base part 20B, here a base plate, interconnecting the branches and extending under the blade root 16. The shim 20 constitutes a wear piece and its main function is to limit wear of the blade root 16 and of the fan disk 2.

In the example of FIG. 2, the shim 20 presents a multilayer structure in its branches 20A and its base part 20B, which structure comprises three layers 31, 32, 33 that adhere to one another. These three layers are superposed in the following order going from the blade root 16 towards the disk 2: a first layer 31 of a first material; a second layer 32 of a second material; and a third layer 33 of a third material. In this example, the third material is identical to the first material, so that they present the same first Young's modulus. In accordance with the invention, at any operating temperature T of the shim, the first Young's modulus has a corresponding value E, and at said temperature T, said second material presents a second Young's modulus with a value lying in the range E/20 to E/5.

It should be observed that the shim 20 must present a certain amount of stiffness in order to perform its mechanical function and its anti-wear function, such that the value of E is preferably greater than or equal to 110,000 megapascals (MPa) for metal shim (e.g. 210,000 MPa for shim made of a nickel-based superalloy, of the type sold under the name “Inconel”), and greater than or equal to 70,000 MPa for shim made of organic matrix composite material.

So far as the choice of materials is concerned, it naturally depends on the operating temperature of the shim.

When the rotor assembly belongs to the fan or the low pressure compressor of a bypass two-spool airplane turbojet, it is subjected to operating temperatures lying in the range 20° C. to 150° C. Under such circumstances, and by way of example, it is possible for the first material to be selected as a Ni-based superalloy with more than 15% by weight Fe and Cr, such as the superalloy sold under the name “Inconel 718”; while the second material can be rubber (natural or synthetic). In these circumstances, it is also possible for the first material to be a composite material using an epoxy resin matrix with reinforcing fibers, e.g. made of carbon; the second material could then be an epoxy resin on its own (with the difference in Young's modulus between the first and second materials being associated with the absence of fibers).

When the assembly belongs to the high pressure compressor of a bypass two-spool airplane turbojet, it is subjected to operating temperatures lying in the range 150° C. to 500° C. Under such circumstances, and by way of example, it is possible to select for the first material a Ni-based superalloy having more than 15% by weight of Fe and Cr, such as the superalloy sold under the name “Inconel 718”; the second material could be a silicone or polyimide.

When the assembly belongs to the high pressure turbine of a bypass two-spool airplane turbojet, it is subjected to operating temperatures lying in the range 400° C. to 700° C. Under such circumstances, and by way of example, it is possible for the first material to be selected as an Ni-based superalloy with more than 15% by weight Fe and Cr, such as the superalloy sold under the name “Inconel 718”; the second material may be glass (which in this operating temperature range presents viscoelastic behavior).

In general, it should be observed that said layers 31, 32, 33 can be fastened to one another in various ways, and in particular:

• • by natural adhesion when polymerizing the second layer 32 (or when vulcanizing it if is made of rubber);
  • by adhesive;
  • by welding the layers 31 and 33 together in part and then polishing them;
  • by brazing the layers 31 and 33 together in part, and then polishing them;
  • by crimping; or
  • by combining the above techniques (e.g. natural adhesion and crimping).

Said layers may be integral with one another to form said multilayer structure, and the fastening that is obtained must naturally be sufficiently secure to prevent the structure becoming delaminated in operation and to prevent the layer 32 from creeping.

FIG. 3 is a section view analogous to that of FIG. 2 showing another element of a shim 120 of the invention. Elements or element portions that are analogous between FIGS. 2 and 3 are identified by the same reference numerals plus 100.

The example of FIG. 3 differs from that of FIG. 2 in that the base part 120B of the shim 120 is formed by the first and second layers 131 and 133 joined to each other. Only the branches 120A of the shim present a multilayer structure made up of the first, second, and third layers 131, 132, and 133 of the invention. It should be observed that the base part 120B of the shim could also be formed solely by the third layer 133, or indeed solely by the first layer 131.

FIG. 4 is a section view analogous to that of FIG. 2 showing another example of a shim 220 of the invention. Elements or element portions analogous between FIGS. 2 and 4 are identified with the same numerical references plus 200.

The example of FIG. 4 differs from that of FIG. 2 in that the base part 220B of the shim 220 extends over the outer periphery of the rotor disk 202 between two adjacent slots 204, with each branch 220A of the shim penetrating into a slot 204 and being housed between the bearing surface 216A of the blade root 216 and the corresponding bearing surface 222A of the disk 202.

The shim 220 presents a multilayer structure analogous to that of the shim 20 in FIG. 2, having three layers 231, 232, 233 that are fastened to one another and superposed.

Claims

1. A shim for a turbomachine blade, the shim comprising two branches for coming against bearing surfaces of the blade rotor, and a base part interconnecting the branches, the shim presenting, at least in its branches, a multilayer structure having at least three layers that are fastened to one another and superposed in the following order: a first layer of a first material; a second layer of a second material; and a third layer of a third material that is optionally different from the first material, said first and third materials presenting respective first and third Young's moduluses of values E and E′ at any arbitrary operating temperature in the operating temperature range of the shim, and said second material presenting a second Young's modulus of value lying in the range E/20 to E/5 and in the range E′/20 to E′/5 at said operating temperature.

2. A shim according to claim 1, in which said first and third materials are identical.

3. A shim according to claim 1, in which said first and third materials are metal alloys or organic matrix composite materials, while the second material is non-metallic.

4. A shim according to claims 1, in which said second material presents viscoelastic behavior in the operating temperature range of the shim.

5. A shim according to claim 1, in which said first, second, and third layers also extend in the base part of the shim.

6. A turbomachine rotor assembly comprising: a rotor disk presenting slots in its outer periphery; blades fastened by their roots in said slots; and shims according to any preceding claim, each branch of each shim being disposed between the bearing surface of a blade root and the corresponding bearing surface of the disk.

7. A turbomachine rotor assembly according to claim 6, in which the base part of each shim extends under each blade root.

8. A turbomachine rotor assembly according to claim 6, in which the base part of each shim extends over the outer periphery of the disk, between two adjacent slots.

9. A turbomachine comprising a rotor assembly according to claim 6.