OUTER SHELL SECTOR FOR A BLADED RING FOR AN AIRCRAFT TURBOMACHINE STATOR, INCLUDING VIBRATION DAMPING SHIMS

Abstract

An assembly forming an outer shell sector, for a bladed ring sector configured to be used on a compressor or turbine stator in an aircraft turbomachine, including a plurality of elementary sectors and vibration damping shims each of them being inserted between two elementary sectors associated with it. A profile of each vibration damping shim is approximately the same as a profile of the elementary sectors.

Description

DESCRIPTION

This invention generally relates to an aircraft turbomachine, preferably of the turbojet or turboprop type.

More particularly, the invention relates to the compressor or turbine stator of such a turbomachine, and more precisely to a bladed ring sector comprising a plurality of stator blades and two concentric shells supporting the blades and designed to radially delimit a primary flow passing through the turbomachine, inwards and outwards respectively. Such a bladed ring is usually made using several sectors arranged end to end, is usually used in the compressor or the turbine as a guide vane or a nozzle.

Turbomachines usually comprise a low pressure compressor, a high pressure compressor, a combustion chamber, a high pressure turbine and a low pressure turbine, in series. Compressors and turbines comprise several rows of mobile blades at a circumferential spacing, these rows being separated by rows of fixed blades also at a circumferential spacing. In modern turbomachines, high dynamic stresses are applied to the guide vanes and nozzles. Technological progress leads to a reduction in the number of stages for equal or better performances, resulting in a higher load for each stage. Furthermore, changes to production technologies have led to a reduction in the number of parts, which reduces the damping effect of connections between parts. This is the case particularly when an abradable cartridge brazing technology is used which eliminates a large source of dissipation of vibration energy.

Document FR-A-2 902 843 discloses a means of solving this vibration problem by breaking the outer shell sector down into elementary sectors at a fixed spacing from each other along the tangential direction by the use of slits or radial cuts, oblique or in another direction, each elementary sector supporting a single blade of the bladed ring sector. Furthermore, damping inserts in the form of strips are inserted between the elementary sectors. The operating principle is based on the introduction of a stiffness non-linearity in the dynamic behaviour of the structure. This non-linearity is triggered by a threshold vibration level of the system. This vibration activity causes a relative movement between the elementary sectors of the blades and the damping inserts. This relative movement causes successive loss and recovery of adhesion of the damping inserts and consequently a continuous variation of the local stiffness of the system. Consequently, the mode(s) causing the vibration activity are disorganised by the permanent variation of the associated natural frequencies. Resonance of the system cannot be set up because of the continuous variation in the state of the dynamic system. This reduces vibration amplitudes in the system.

Nevertheless, even if this solution is satisfactory in terms of reducing vibrations, it can be improved. Furthermore, in this solution disclosed in document FR-A-2 902 843, the damping inserts are held in contact against the friction surfaces of the elementary sectors due to the effect of the pressure gradient between the aerodynamic flowpath and the outside of the compressor, applying a radially inwards force on these inserts. The disadvantage is that this pressure gradient cannot be sufficient to satisfactorily force the inserts into contact with the friction surfaces. In this case, the result is firstly a reduction in the vibration damping performances, but also a possible loss of leak tightness of the air flowpath.

Another disadvantage with this solution is the fact that one of the blades in the bladed ring sector will be overloaded. Aerodynamic forces applied on the blades include a tangential component that cannot be resisted in the outer shell sector, due to its segmentation into tangentially spaced elementary sectors. Thus, these tangential components are combined and pass through the inner shell sector of the bladed ring sector before passing through the blade located adjacent to the anti-rotation stop fitted on the ring sector. Therefore, this blade is very highly loaded due to the incapability of the outer shell sector to transmit static forces along the tangential direction.

Therefore, the purpose of the invention is to at least partially overcome the problems mentioned above that arise with embodiments according to prior art.

The first purpose of the invention to achieve this is an assembly forming an outer shell sector for a bladed ring sector that will be used on a compressor or turbine stator in an aircraft turbomachine, said outer shell sector comprising firstly a plurality of elementary sectors at a spacing from each other along a tangential direction of said assembly, and secondly vibration damping shims, each of them being inserted between two elementary sectors associated with it, placed directly consecutively along said tangential direction.

According to the invention, the profile of each vibration damping shim is approximately the same as the profile of the elementary sectors.

Due to the particular profile of the shims, the friction interface between the shims and the elementary sectors is large which results in an improved damping effect.

Furthermore, the fact that the shims are forced into contact with the friction surfaces of the elementary sectors can result in a perfect seal between these elements, independent of the pressure difference between the aerodynamic flowpath and the outside of the compressor or the turbine. This seal is obtained by construction, with shims applying forces on the friction surfaces of the elementary sectors approximately along the tangential direction. Note that this seal is further reinforced during operation, because the forces bringing the friction surfaces and the shims into contact with each other are accentuated by application of the tangential component of aerodynamic forces applied on the stator blades, on the elementary sectors.

Concerning the tangential component of the aerodynamic forces applied on the blades, note that one of the essential advantages of this invention lies in the fact that this component can transit through the assembly forming an outer shell sector because the outer shell sector is very much stiffened along the tangential direction due to the particular positioning of vibration damping shims, even though it is separated into sectors along this direction. The result is that there is no overload of the blades that are therefore loaded approximately uniformly.

Finally, note that by adopting approximately the same profile as the profile of the elementary sectors, the outer radial delimitation of the primary annular flow, also called the air flowpath, is perfectly recreated between the elementary sectors at a spacing from each other.

Preferably, said shim bears in contact with two parallel plane friction surfaces facing each other along said tangential direction and provided on said two elementary sectors associated with said shim, and said shim has two complementary plane friction surfaces parallel to each other and cooperating with the two corresponding friction surfaces of the elementary sectors. The plane contacts between the friction surfaces and the complementary friction surfaces give satisfactory damping of vibrations by friction. It is also possible to make the two friction surfaces simultaneously during a single machining operation, for example by a single cutting operation, in order to obtain straight slits, in other words slits in a determined plane, inside which the corresponding shims will subsequently be housed. This makes it very much simpler to fabricate the assembly according to the invention, which results in a significant cost and time saving.

Preferably, said shim is provided with hooks to hold it in place on the compressor or turbine stator, therefore these hooks have the same profile as the hooks fixed on the elementary sectors.

Preferably, the elementary sectors are separated from each other by radial slits completely filled in by said vibration damping shims.

Preferably, said vibration damping shims extend approximately along an axial or oblique direction of said assembly.

Another purpose of this invention applies to a bladed ring sector designed to be installed on a compressor or turbine stator of an aircraft turbomachine comprising an assembly forming an outer shell sector like that described above, an inner shell sector and a plurality of blades at a tangential spacing from each other and inserted between the assembly forming the outer shell sector and the inner shell sector. In this case, each elementary sector will carry a single stator blade, or possibly several blades, without going outside the scope of the invention.

The bladed ring may form a guide vane of a compressor or a nozzle of a turbine.

Furthermore, the ring sector preferably extends around an angular range of between 5 and 60°, but can be as much as 360° so as to form the entire bladed ring.

Another purpose of the invention is an aircraft turbomachine comprising a compressor or turbine stator equipped with at least one bladed ring sector like that described above.

Other advantages and characteristics of the invention will appear in the detailed non-limitative description given below.

This description will be made with reference to the appended drawings among which;

FIG. 1 shows a diagrammatic sectional view of a turbomachine that will be equipped with one or several bladed ring sectors according to this invention;

FIG. 2 shows a sectional view representing part of the high pressure compressor of the turbomachine shown in FIG. 1, and including a bladed ring sector according to this invention;

FIG. 3 shows a perspective view of the bladed ring sector shown in the previous figure, the sector being in the form of a preferred embodiment of this invention;

FIG. 4 shows an axial view of part of the bladed ring sector shown in the previous figure;

FIG. 5 shows a profile view of the shims and the elementary sectors of the bladed ring sector shown in the previous figures, along line V-V in FIG. 4; and

FIGS. 6a to 6c show views diagrammatically showing the different steps in a fabrication process of the bladed ring sector shown in the previous figures.

With reference firstly to FIG. 1, the figure shows an aircraft turbojet 100 to which the invention is applicable. It comprises, in order along the upstream to downstream direction, a low pressure compressor 2, a high pressure compressor 4, an annular combustion chamber 6, a high pressure turbine 8 and a low pressure turbine 10.

FIG. 2 shows part of the high pressure compressor 4. In a known manner, the compressor comprises rows 14 of stator blades and rows 16 of rotor blades alternating on an axial direction parallel to the axis 12 of the compressor. The stator blades 18 distributed circumferentially/tangentially around the axis 12, are included in a part of the stator called the bladed ring 20, preferably constructed in sectors along the circumferential direction 22. Thus, in the following we will refer to a bladed ring sector 20, it being understood that this sector 20 preferably extends over an angular range of between 5 and 60°, but possibly as much as 360° so as to form the entire bladed ring.

The sector 20, therefore forming all or part of a turbine nozzle or a compressor guide vane, comprises an inner shell sector 24 forming the inner surface radially delimiting a primary annular flow 26 passing through the turbomachine, this shell sector 24 supporting the fixed roots of the stator blades 18. In addition to these blades 18, the sector 20 also comprises an assembly forming an outer shell sector 28 forming the outer surface radially delimiting the primary annular flow, and supporting the fixed heads of the blades 18.

In this respect, note that the sector 20 also comprises known additional elements fitted on the shell sector 24, such as a radially internal abradable coating 29 forming the annular sealing track contacted by a sealing device 31 supported by the rotor stage 16 supporting the rotating blades and arranged on the downstream side of the sector 20 concerned. The rotating sealing device 31 is a known labyrinth or lip seal type sealing device.

FIG. 3 shows the bladed ring sector 20. In the preferred embodiment described, the entire turbine nozzle or compressor guide vane is obtained by end to end placement of a plurality of these sectors 20, therefore each forming an angular or circumferential portion of this bladed ring. The angular sectors 20 (only one of which can be seen in FIG. 3) are preferably deprived of any rigid direct mechanical links connecting them to each other, their adjacent ends being simply placed facing each other with or without clearance.

More specifically with reference to FIGS. 3 and 4, the figures show that the inner ring sector 24 is made in a single part and is not segmented. On the other hand, the assembly 28 forming the outer shell sector 28 is segmented into elementary sectors 30 at a spacing from each other along the tangential direction 22, by straight radial or slightly oblique slits 32, therefore creating clearances between the directly consecutive sectors 30. Each slit 32 is made along a median straight line between two directly consecutive blades 18, such that each elementary sector 30 supports a single fixed stator blade 18. One of the two elementary sectors 30 located at the ends of the sector 20 supports a rotation stop 33 projecting radially outwards and that will cooperate with another part of the compressor stator in a known manner.

The assembly 28 also comprises vibration damping shims 34 housed between directly consecutive elementary sectors 30.

More precisely, each vibration damping shim is housed between two plane parallel friction surfaces 38 facing each other along the tangential direction 22, and provided on the corresponding tangential ends facing each other on the two elementary sectors associated with the shim. Similarly, each shim has two complementary plane friction surfaces 40 parallel to each other and also parallel and in contact with the two corresponding plane friction surfaces 38 with which they cooperate.

Therefore, each shim 34 is squeezed between two directly consecutive elementary sectors 30, having a shape complementary with the shape of the friction surfaces 38.

The contact between the two friction surfaces 38, 40 of each pair is preferably obtained as soon as the shim 34 is put into position between its two associated elementary sectors 30. The shims 34 thus apply forces oriented approximately along the tangential direction in contact with the friction surfaces 38 of the elementary sectors, with their complementary plane friction surfaces 40. These forces are advantageously increased during operation by the additional application of the tangential component of aerodynamic forces applied on the stator blades, on the elementary sectors.

As shown diagrammatically in FIG. 5, one of the special features of this invention lies in the fact that the profile of the shims 34 is approximately the same as the profile of the elementary sectors, this same profile corresponding to the profile of the outer shell sector. In this disclosure, profile refers to the global shape of the element seen along the tangential direction 22, although a sectional view is shown in FIG. 5.

Thus, the lower surface 46 of each shim 34, like the elementary sectors 30, acts as the outer radial delimitation of the air flowpath. Consequently, the global annular delimitation surface of the air flowpath composed of the sequence of these surfaces 46 formed on the shims 34 and the sectors 30, is approximately continuous from an aerodynamic point of view because there is no step between the successive surfaces 46.

Each shim 34 and each sector 30 also comprises hooks to hold it in place on another part of the compressor stator, and more precisely a fixing hook 48 projecting forwards, and a fixing hook 50 projecting backwards. As shown in FIG. 2, the hooks 48, 50 are housed in the corresponding annular slits 52, 54 provided in another part of the compressor stator, to fix the sector 20 onto this other part of the stator.

The shims 34, entirely filling in the slits 32, perform a vibration damping function by friction in contact with the friction surfaces 38, based on the physical principle described above for the shims disclosed in document FR-A-2 902 843. They also perform a seal function, and a function to allow the tangential component of aerodynamic forces applied on the stator blades to pass through. More generally in this respect, each shim 34 is capable of transmitting tangential forces between the two elementary sectors 30 between which it is inserted.

The natures of the materials used for the elementary sectors 30 and for the shims 34 are approximately the same, preferably metallic, and are chosen such that the shims wear preferentially rather than the elementary sectors 30.

Note also that the ratio between the extent of each shim and the extent of each elementary sector along the tangential direction that also correspond to the thicknesses, is between 0.5 and 1.

FIGS. 6a to 6c diagrammatically show a process for fabrication of the bladed ring sector 20. Firstly as can be seen in FIG. 6a, a single-piece assembly 100 is made by pouring or machining forming the inner shell sector 24, the outer shell sector 28 and the stator blades 18. The next step is to make straight radial slits 32 on the outer shell sector 28 so as to obtain the elementary sectors 30 as shown diagrammatically in FIG. 6b, by simple and inexpensive machining. For example, these slits 32 can be made simply by cutting the sector 28.

Finally, FIG. 6c shows the final step that consists of putting the vibration damping shims 34 into position in the slits 32 forming the friction surfaces, simply by sliding the shims into their corresponding holes.

Note that a precise sliding adjustment clearance is preferred to make it relatively easy to insert of each shim in its associated slit while holding this shim in its slit solely by the squeezing force between the two friction surfaces 38.

Obviously, those skilled in the art could make various modifications to the invention as described above, solely using non-limitative examples.

Claims

1-7. (canceled)

8. A bladed ring sector configured to be installed on a compressor stator of an aircraft turbomachine, comprising:

an assembly forming an outer shell sector;

an inner shell sector;

a plurality of blades at a tangential spacing from each other and inserted between the assembly forming the outer shell sector and the inner shell sector, the blades being fixed to each assembly forming the outer shell sector and the inner shell sector; and

the assembly forming an outer shell sector comprising firstly a plurality of elementary sectors at a spacing from each other along a tangential direction of the assembly, and secondly vibration damping shims each of them being inserted between two elementary sectors associated with it, placed directly consecutively along the tangential direction,

wherein a profile of each vibration damping shim is approximately a same as a profile of the elementary sectors.

9. A sector according to claim 8, wherein the shim is forced in contact with two parallel plane friction surfaces facing each other along the tangential direction and provided respectively on the two elementary sectors associated with the shim, and wherein the shim has two complementary plane friction surfaces, parallel to each other and cooperating with the two corresponding friction surfaces of the elementary sectors.

10. A sector according to claim 8, wherein the shim includes hooks to hold it in place on the compressor or turbine stator.

11. A sector according to claim 8, wherein the elementary sectors are separated from each other by radial slits completely filled in by the vibration damping shims.

12. A sector according to claim 8, wherein the vibration damping shims extend approximately along an axial or oblique direction of the assembly.

13. An aircraft turbomachine comprising:

a compressor stator including at least one bladed ring sector according to claim 8.