FR3137121A1 - Bladed assembly with inter-platform connection by interposed rolling element - Google Patents

Abstract

A bladed assembly (40) for a turbomachine rotor comprises a plurality of blades (42) distributed around an axis (28) and each comprising a blade (44), and a platform (46) at the end of the blade comprising a first hollow (56) and a second hollow (60), so that the first hollow (56) is arranged radially opposite the second hollow (60) of the platform of a circumferentially adjacent blade. A rolling element (70) is housed in the first hollow (56) of the platform of each blade and the second hollow (60) of the platform of the adjacent blade. In operation, the points of contact between the rolling element and the hollows can move on the surface of the rolling element, thus inducing non-linearity in the dynamic behavior of the bladed assembly such as to limit the amplitude of vibrations of the latter. Figure for abstract: Figure 4

Description

Bladed assembly with inter-platform connection by interposed rolling element

The present invention relates to the general field of bladed assemblies within turbomachines, in particular turbomachines intended for aircraft propulsion.

It concerns more particularly the damping of vibrations appearing in operation between the platforms of two circumferentially adjacent blades of a bladed assembly.

State of the prior art

A bladed assembly of a turbomachine, for example a movable bladed assembly of a low-pressure turbine stage of a turbojet, comprises a disk on which blades are mounted.

At their external radial end, also called the top, the blades each have a transverse element, called a platform, which has the particular function of externally delimiting the flow path of the gas flow passing through the turbine or, more generally, the part concerned. of the turbomachine.

The platform of such a blade has an upstream edge and a downstream edge oriented perpendicular to the direction of flow of the gas flow. These edges are connected to each other via two lateral edges forming the circumferential ends of the platform and by which the platform of the blade comes substantially into contact with the platforms of the two blades of the bladed assembly which are directly adjacent to it. circumferentially.

A known solution for limiting the vibrational constraints on such blades consists of providing each of these lateral edges with a complex profile comprising non-axial portions, that is to say not parallel to the axis of rotation of the assembly. bladed, and comprising for example additional outgrowths and impressions. Indeed, in order to dampen the vibrations to which the blades are subjected during operation of the turbine, it is known to mount the blades on the disk with a torsional constraint around their main axis. At the level of the platform of a particular blade, this torsional stress results in bringing non-axial portions of the platform of the blade into contact with non-axial portions of the platforms of neighboring blades. The vibrations of the blades in operation induce relative sliding at the level of these contact zones, which, coupled with the contact pressures, create friction damping. This type of configuration is sometimes referred to as “interlock”.

With this type of solution, the inter-platform contact force can evolve during operation, in particular due to a natural rotation of the blade around its mean line, and due to a relative movement between circumferentially adjacent platforms leading these last to come closer or move away.

In the particular case where the contact force is reduced in operation compared to the situation when stopped, it is necessary to amplify this contact force when assembling the blades to obtain a desired force level at high speed. , where the need for vibration damping is most felt. Such an adaptation results in static overloads applied to the blades.

This is particularly detrimental in the case of blades made of composite material, in particular CMC (ceramic matrix composite), due to relatively low admissible stress levels for this type of material, which make the blades poorly tolerant to pre-twisting. Thus, for a CMC blade, strong pre-torsion during assembly induces high static stresses compared to the admissible level, and sometimes even beyond the latter.

Furthermore, this type of material expands considerably less than the metallic materials from which the blades have conventionally been manufactured. In the case of blades having platforms configured as indicated above, this results in a spacing of the circumferentially adjacent platforms when hot and therefore in a reduction in the contact force in operation.

Means of damping the vibrations of turbomachine blades while overcoming the difficulties explained above relating to the pre-twisting of the blades have been proposed by the applicant. The general idea then consists of not having cold contact between circumferentially adjacent blades, but of generating such hot contact.

Document FR2956152 describes an example of a solution of this type, in which the contact between two circumferentially adjacent platforms is made by a damping part mounted with a certain radial clearance under one of the platforms and coming to support under the other platform under the effect of centrifugal force in operation and thus exert friction forces.

The solution presented in this document, however, has a drawback in that the damping part extends partially in the flow path of the gas flow and thus constitutes a cause of disturbances in this gas flow.

The document FR2955142 describes another example, in which the damping part has ends housed within cavities formed within the circumferentially adjacent platforms, also with a certain radial play, so as to come to bear against the wall delimiting each of the cavities under the effect of centrifugal force in operation.

Due to the fact that the cavities extend in the circumferential direction and have a closed section transversely to the circumferential direction, the solution presented in this document makes it possible to introduce dissipation by friction due to the relative movements of the platforms. This solution is not intrusive in the gas flow. On the other hand, this solution leads to a heavier platform due to the relatively large volume of material required to form the cavities and the damping part, which is detrimental to the stability of the blade.

The document FR2955608 describes yet another example, in which the damping part is a sheet having ends housed within cavities formed within the circumferentially adjacent platforms, so as to come to bear against the wall delimiting each of the cavities under the effect of centrifugal force in operation. This solution therefore also makes it possible to limit the possibilities of mutual separation of the two platforms in the direction of the axis of rotation of the bladed assembly.

The aim of the invention is to provide a solution for reducing the vibrations of bladed turbomachine assemblies, in particular those whose blades are made of composite material such as a ceramic matrix composite material (CMC), making it possible in particular to limit as best as possible the mechanical stresses applied to the blades and to avoid all or part of the disadvantages mentioned above.

For this purpose, it proposes a bladed assembly for a turbomachine, comprising a plurality of blades distributed circumferentially around an axis and each comprising a blade and a platform formed at a free end of the blade, and in which:

• the platform of each blade comprises a first hollow and a second hollow, the first hollow being arranged radially opposite the second hollow of the platform of a circumferentially adjacent blade; And
• a rolling element is housed in the first hollow of the platform of each blade and the second hollow of the platform of the circumferentially adjacent blade.

In operation, depending on the type and amplitude of the vibrations of the blade platforms, contact between the rolling element and one and/or the other of the hollows may occur, and the points of contact between the rolling element and the hollow(s) can move on the surface of the rolling element. Given the convexity of this surface, such displacements induce a non-linearity in the dynamic behavior of the platforms, and therefore of the bladed assembly, likely to limit the amplitude of the vibrations. Indeed, the geometry of the connection between circumferentially adjacent blades is thus made dependent on the amplitude and shape of the vibrations of the blades, which makes it possible to avoid or at least limit the establishment of vibration resonances. Unlike known solutions in which vibration damping is obtained by means of friction between adjacent blades, vibration damping is here obtained due to the non-linearity of the dynamic behavior of the bladed assembly.

In embodiments of the invention, at least one, and preferably each, among the first hollow and the second hollow, has a concave shape in at least one cutting plane including the axis and a radial direction relative to to the axis.

In embodiments of the invention, at least one, and preferably each, among the first hollow and the second hollow, has a concave shape in at least one cutting plane including a circumferential direction relative to the axis .

In embodiments of the invention, at least one, and preferably each, among the first hollow and the second hollow, has a concave shape in at least one cutting plane including a radial direction relative to the axis , in particular a plane including the axis of the bladed assembly and/or a plane including a circumferential direction relative to the axis.

In embodiments of the invention, said concave shape is axisymmetric.

In embodiments of the invention, at least one of the first hollow and the second hollow is delimited by a rim.

In embodiments of the invention, said rolling element is a ball.

In other embodiments of the invention, said rolling element is an axis pin locally orthogonal to a radial direction relative to the axis.

In embodiments of the invention, the platform of each blade comprises:

• an external surface comprising the first recess and, at one circumferential end, a rim extending radially outwardly, and
• an engagement portion projecting circumferentially from said rim and having an internal surface comprising the second recess.

The invention also relates to a turbine for a turbomachine, comprising at least one bladed assembly of the type described above.

The invention also relates to a turbomachine, comprising at least one turbine of the type described above.

The invention will be better understood, and other details, advantages and characteristics thereof will appear on reading the following description given by way of non-limiting example and with reference to the appended drawings in which:

is a schematic view in axial section of a turbomachine;

is a partial schematic perspective view of a bladed assembly for a turbomachine according to a preferred embodiment of the invention, seen radially from the outside, showing in particular respective blade platforms of the bladed assembly;

is a partial schematic perspective view of a blade of the bladed assembly of the , viewed radially from the interior;

is a partial schematic perspective view of the dawn of the , seen radially from the outside;

is a partial schematic view in perspective and in cross section of the bladed assembly of the , showing two adjacent blades of this bladed assembly;

is a partial schematic view in cross section of the bladed assembly of the , showing the junction region between two blades and a disc of said bladed assembly.

In all of these figures, identical references can designate identical or similar elements.

Detailed presentation of preferred embodiments

There illustrates a turbomachine 10, for example a dual-flow, dual-body turbojet for an aircraft, generally comprising a fan 12 intended for suction of an air flow F1 dividing downstream of the fan into a primary flow F2 circulating in a primary flow flow channel, hereinafter referred to as primary vein PV, and a secondary flow F3 circulating in a secondary flow flow channel, hereinafter referred to as secondary vein SV, arranged around the primary vein PV.

The turbomachine generally comprises a low pressure compressor 14, a high pressure compressor 16, a combustion chamber 18, a high pressure turbine 20 and a low pressure turbine 22 which jointly define the primary stream PV.

The respective rotors of the high pressure compressor and the high pressure turbine are connected by a shaft called a “high pressure shaft”, while the respective rotors of the low pressure compressor and the low pressure turbine are connected by a shaft called a “low pressure shaft”. ”, in a well-known manner. These rotors are rotatably mounted around an axis 28 of the turbomachine.

Throughout this description, the axial direction is at all points a direction orthogonal to the radial direction R and to axis 28. A transverse plane is a plane orthogonal to axis 28. The terms "internal" and "external" respectively refer to a relative proximity, and a relative distance of an element from axis 28. Finally, the “upstream” and “downstream” directions are defined by reference to the general direction of the flow of gases in the primary PV and secondary SV veins of the turbomachine, in the axial direction X.

Figures 2-4 illustrate a bladed assembly 40 for a turbomachine rotor, for example intended to be used within the low pressure turbine 22 of the turbomachine 10 of the or another turbomachine component.

Such a bladed assembly comprises an annular row of blades 42 distributed around an axis of the bladed assembly which merges with the axis 28 when the bladed assembly is mounted within a turbomachine and for example mounted on a corresponding rotor disk.

Each blade 42 comprises in particular a blade 44 and a platform 46 formed at the radially outer end of the blade 44. With reference to the , such a blade 42 also typically comprises a platform 43A arranged at the base of the blade 44 and a foot 43B arranged under the platform 43A to allow the mounting of the blade in a disk 41 of the bladed assembly 40.

The blades 44 of the blades have an aerodynamic profile which allows them to interact with the gases circulating in the primary vein PV.

The main function of the platforms 46 is to externally delimit the primary vein PV by means of respective internal surfaces 50 of the platforms, and to limit as best as possible gas leaks around the bladed assembly 40 in order to maximize the interaction between the gas and the blades 44. For this purpose the platforms 46 typically comprise ribs 48, commonly referred to as sealing strips, formed projecting radially outwards from respective external surfaces 54 of the platforms, and the ends of which are intended to dig holes. corresponding grooves within a ring of abradable material arranged around the bladed assembly 40 within a turbomachine.

Like the platforms of known bladed assemblies, each of the platforms 46 has two circumferential ends 55A, 55B respectively facing corresponding circumferential ends of the two platforms which are circumferentially adjacent to it.

The bladed assembly 40 has the particularity of offering a new mode of limiting the amplitude of the vibrations of the blades 42, consisting of connecting the platforms 46 two by two in a manner inducing non-linearity which makes it possible to maintain the all of the blades 42 in an unestablished vibration regime.

For this purpose, the platform 46 of each blade comprises a first hollow 56 and a second hollow 60, arranged so that the first hollow 56 of the platform 46 of each blade is arranged radially opposite the second hollow 60 of the platform of a circumferentially adjacent blade. In addition, a rolling element 70 is partially housed in the first hollow 56 of the platform of each blade and in the second hollow 60 of the platform of the adjacent blade. It should therefore be understood that the rolling element 70 is housed in a virtual volume delimited, on one radial side, by the first hollow 56, and delimited, on an opposite radial side, by the second hollow 60, whereby the rolling element is trapped in said volume under normal operating conditions, that is to say in the absence of deformation of the platforms 46 beyond a maximum admissible deformation threshold in operation.

More precisely, in the illustrated embodiment, the platform 46 of each blade 42 comprises an engagement part 52 extending circumferentially projecting from one of the circumferential ends 55A of the platform.

The external surface 54 of the platform 46 includes the first hollow 56 ( ).

The engagement part 52 is offset radially outwards relative to the external surface 54 and has an internal surface 58 comprising the second recess 60 ( ). The internal surface 58 thus faces radially the external surface 54 of the platform 46 of the adjacent blade.

The engagement part 52 is thus located outside the primary vein PV, which is preferable so as not to disturb the gas flow within the vein.

The platform 46 of each blade 42 is shaped so that the first hollow 56 thereof is arranged radially opposite the second hollow 60 of the platform of a circumferentially adjacent blade ( ). For this purpose, the platform 46 of each blade comprises for example, at the circumferential end 55A, a rim 64 extending radially outwards relative to the external surface 54 and from which the engagement part 52, in the form of a tab or blade, projects circumferentially beyond the circumferential end 55A.

The term "rolling" does not imply that the rolling element 70 actually rolls along the surfaces 54 and 58 in operation but that the shape of said element allows it to roll in at least one direction along the surfaces 54 and 58. Otherwise said, the rolling element 70 has a convex section in at least one section plane including the radial direction R, for example in a transverse section plane P1 (that is to say orthogonal to the axis 28 and therefore including the circumferential direction C, see ) and/or in an axial section plane P2 (that is to say including axis 28).

Analogously, at least one, and preferably each, among the first hollow 56 and the second hollow 60, has a concave shape in at least one cutting plane including the radial direction R. Thus, at least one among the first hollow 56 of each blade 42 and the second hollow 60 of the adjacent blade is concave towards the other hollow opposite which it is arranged.

In the illustrated embodiment, the rolling element 70 is a ball and therefore has a spherical shape. Analogously, each of the hollows 56 and 60 has an axisymmetric concave shape, with an axis oriented substantially in the radial direction R. In other words, each of the hollows 56 and 60 is in the shape of an inverted dome and is therefore in particular concave at the both in the transverse cutting plane P1 and in the axial cutting plane P2.

In operation, under the effect of centrifugal force, the rolling element 70 is generally pressed against the second hollow 60. Depending on the type and amplitude of the vibrations of the platforms 46 of the two blades considered, contact between the element rolling element 70 and the first hollow 56 can also intervene, and the points of contact between the rolling element 70 and each of the hollows 56 and 60 can move on the surface of the rolling element 70. Taking into account the convexity of this surface , such movements induce a non-linearity in the dynamic behavior of the platforms 46, such as to limit the amplitude of the vibrations of the latter. Indeed, the geometry of the connection between circumferentially adjacent blades is thus made dependent on the amplitude and shape of the vibrations of the blades, which makes it possible to avoid or at least limit the establishment of vibration resonances.

Unlike known solutions in which vibration damping is obtained by means of friction between adjacent blades, vibration damping is here obtained due to the non-linearity of the dynamic behavior of the bladed assembly.

Furthermore, at least one of the hollows 56 and 60, for example the first hollow 56, can be delimited by a rim 72 formed projecting from the corresponding surface, in this case the external surface 54. Such a rim allows that the rolling element 70 remains trapped in its housing corresponding to the virtual volume defined between the recesses 56 and 60, even in the event of high amplitude vibrations, which makes it possible to avoid the loss of the rolling element 70.

Alternatively, the concave shape of one of the recesses 56 and 60 or of each of these recesses may not be axisymmetric. Thus, one of the recesses 56 and 60 or each of these recesses can for example be in the shape of an inverted dome elongated in a given direction orthogonal to the radial direction R or in the shape of a groove of constant section in said given direction.

More generally, said concave shape can be concave in a section plane including the radial direction R and a given direction orthogonal to the radial direction R, for example the transverse plane P1 or the axial plane P2, and not be concave in another cutting plane orthogonal to said given direction, or even present a greater extent in this other cutting plane than in the cutting plane including said given direction.

The aforementioned given direction can advantageously be chosen to correspond to the direction of a vibration mode of the blade within the bladed assembly in operation, preferably a vibration mode having the lowest frequency among the vibration modes of the blade. dawn, such a mode of vibration generally being the most harmful.

Furthermore, the rolling element 70 can be a pin and thus have a cylindrical shape, with an axis for example parallel to the axial direction of groove elongated in the direction of the axis of the rolling element 70 and with a concave section orthogonally to said axis.

Finally, the assembly of the bladed assembly can be carried out in different ways.

A first way may consist of introducing the feet 43B of the blades 42 little by little into corresponding cells of the disc 41, each rolling member 70 being positioned from the start of the process between the first and second hollows 56 and 60 correspondents.

Another way consists of taking advantage of the flexibility of the engagement parts 52 and the blades 44 of the blades to separate the surfaces 54 and 58 and insert the rolling elements 70 after the blades 42 have been placed on the disc 41.

Yet another way consists of constructing the bladed assembly 40 comprising all the blades 42 and the corresponding rolling elements 70 on a temporary support provided for this purpose, without the disc 41, then putting the disc in place by simultaneously inserting the feet 43B of all the blades in the cells of the disc.

It should be noted that the invention is of course also applicable to bladed assemblies in which the free ends of the blades are the radially internal ends of the latter, for example for contra-rotating turbines. In this case, the configuration of the platforms is preferentially reversed with respect to the radial direction. Thus, the first hollow is in this case preferentially formed in an internal surface of each platform, and the engagement part of each platform is preferentially offset radially inward relative to said internal surface of the platform and preferentially presents a surface external in which the second hollow is formed.

The invention can also be applied to static bladed assemblies.

Claims (10)

Bladed assembly (40) for a turbomachine, comprising a plurality of blades (42) distributed circumferentially around an axis (28) and each comprising a blade (44) and a platform (46) formed at a free end of the blade (42), and in which:

• the platform (46) of each blade (42) comprises a first hollow (56) and a second hollow (60), the first hollow (56) being arranged radially opposite the second hollow (60) of the platform (46) a circumferentially adjacent blade (42); And
• a rolling element (70) is housed in the first hollow (56) of the platform (46) of each blade (42) and the second hollow (60) of the platform (46) of the circumferentially adjacent blade (42).

Bladed assembly according to claim 1, in which at least one of the first hollow (56) and the second hollow (60) has a concave shape in at least one cutting plane including the axis (28) and a radial direction (R) relative to axis (28). Bladed assembly according to claim 1 or 2, in which at least one of the first hollow (56) and the second hollow (60) has a concave shape in at least one cutting plane including a circumferential direction (C) relative to to the axis (28). Bladed assembly according to claim 2 or 3, in which said concave shape is axisymmetric. Bladed assembly according to any one of claims 1 to 4, in which at least one of the first hollow (56) and the second hollow (60) is delimited by a rim (72). Bladed assembly according to any one of claims 1 to 5, wherein said rolling element (70) is a ball. Bladed assembly according to any one of claims 1 to 5, in which said rolling element (70) is an axis pin locally orthogonal to a radial direction (R) relative to the axis (28). Bladed assembly according to any one of claims 1 to 7, in which the platform (46) of each blade (42) comprises:

• an external surface (54) comprising the first recess (56) and, at one circumferential end (55A), a rim (64) extending radially outwardly, and
• an engagement portion (52) projecting circumferentially beyond the circumferential end (55A) from said rim (64) and having an internal surface (58) including the second depression (60).

Turbine (22) for a turbomachine, comprising at least one bladed assembly (40) according to any one of claims 1 to 8. Turbomachine (10), comprising at least one turbine (22) according to claim 9.