Patent Application
20090074569
The present invention relates to turbomachines such as those used in the field of aeronautical engineering. It relates to the variable-pitch stator vanes of turbomachines, particularly of gas turbine engine compressors, and more especially to the control levers that rotate such vanes about their pivot.
Gas turbine engines comprise an air-compressor-forming section feeding a combustion chamber which produces hot gases which, downstream, drive the turbine stages. The engine compressor comprises a plurality of moving bladed disks or blisks, separated by successive stages of stator blisks that straighten the gaseous flow. The vanes of the first flow straightener stages are generally variable-pitch vanes, that is to say that the angular position of the vane about its radial axis, that acts as a pivot, can be adjusted according to mission points in order to improve compressor efficiency. The variable-pitch vanes are oriented using a mechanism known as a variable-pitch mechanism or a VSV which stands for variable stator vane. There are various designs of such mechanisms, but on the whole, they all comprise one or more actuators fixed to the engine casing, synchronization bars or a control shaft, rings surrounding the engine and positioned transversely with respect to the axis thereof, and substantially axial levers also known as pitch control rods, connecting the rings to each of the variable-pitch vanes. The actuators rotate the rings about the engine axis and these cause all the levers to turn synchronously about the vane pivots.
These mechanisms are subjected both to the aerodynamic loads applied to the vanes, which are high, and to loads resulting from friction in the various connections. In particular, the levers are subjected to static loadings in bending and in torsion and to dynamic stresses. All of these loads may reach levels liable to be damaging; in particular, their combined effect may lead to the formation of cracks or to other damage. Given the mechanical strength and endurance requirements attributed to them, the amplitudes of any vibrations caused by these loads, and to which these components are subjected, need to remain small.
The components are designed and engineered in such a way as to avoid there being any critical modes in their operating range. However, in practice, there are still some overlaps and experience, during engine testing carried out at the end of the component design cycle, has revealed that, in some cases, that could lead to cracks being formed in the levers. The component has then to be re-engineered and modified, this being a particularly lengthy and expensive process. It is therefore necessary to predict the vibrational response levels as early on as possible in the component engineering cycle so that the necessary corrective measures can be taken as early on as possible in the design process.
One object of the present invention is to provide structural damping with a view to reducing the levels of deformation experienced by these components during operation and, more specifically, to attenuate the dynamic responses of levers used to rotate a variable-pitch vane under synchronous or asynchronous stress, be it of aerodynamic origin or otherwise, by providing dynamic damping.
The invention thus relates to a lever for rotating about its pivot a turbomachine variable-pitch stator vane comprising three zones: a first zone for attachment to a lever drive member, a second zone for attachment to said variable-pitch stator vane, and a third zone of elongate shape between the first zone and the second zone. The lever according to the invention is one wherein a vibration-damping laminate is applied to at least one surface portion of at least one of said zones of the lever, the laminate comprising at least one layer of viscoelastic material in contact with said surface portion and a backing layer of rigid material.
The drive member is generally a ring surrounding the turbomachine casing, and itself rotated about the axis of this turbomachine by an actuator. The lever is generally mounted at the end of the vane so as to turn the vane via its platform.
The laminate is either bonded onto said surface portion or kept pressed against it by a mechanical means.
In order to guarantee the robustness of these components with respect to vibrational fatigue, the solution of the invention is therefore to add to the structure specific devices capable of dissipating vibrational energy.
The novelty of the present invention lies in its use of tile-like laminates made up of a viscoelastic sandwich with a stress layer which are bonded or fixed to the structure, and the function of which is to dissipate the vibrational energy of the component.
The dissipation of this part of the energy is obtained by shear deformation of the viscoelastic material, between the structure which deforms under dynamic stressing and the stress layer carried along by inertia. These tile-like laminates, by being fixed or bonded to the faces of the lever, directly damp the modes of the structure, without disrupting the overall performance of the machine.
The solution of the invention has the advantage of allowing the structural damping of the metal component in question to be increased without having to re-engineer it, and therefore of reducing the development and optimization costs and time associated with the product.
It also makes it possible to broaden the conventional design domains restricted by the need to meet reverse-cycle loading requirements and, indirectly, allows weight savings.
The invention can be applied irrespective of the type of dynamic loading: overlap with engine harmonics or asynchronous excitation.
According to one embodiment of the invention, said zone of the lever to which the laminate is applied is the third zone. According to technical considerations, said surface portion to which the vibration-damping laminate is applied entirely covers said third zone.
According to another embodiment, said zone of the lever comprises the second and third zones.
According to another embodiment, with the lever comprising a radially upper face and a radially lower face, the laminate is applied to at least one surface portion of said radially lower or upper faces. For example, at least one of said radially lower or upper faces is a flat face.
According to another embodiment, with the second zone of the lever comprising a face at a level radially different than a face of the third zone, the vibration-damping laminate at least partially covers a surface portion of said face of the second zone and a surface portion of said face of the third zone. More particularly, the laminate comprises an intermediate part, between said second zone surface portion and said third zone surface portion. Said intermediate part of the vibration-damping laminate may possibly be holed.
According to one embodiment, the vibration-damping laminate is in the form of a strip of a width narrower than the width of the third zone. The lever may possibly comprise at least two strips of vibration-damping laminate. More specifically, the lever comprises at least two strips of vibration-damping laminate which are positioned parallel to one another.
According to one embodiment, the laminate is made up of a stack of viscoelastic layers and of rigid layers in alternation, and the characteristics of the viscoelastic material vary from one layer to another or alternatively, the characteristics of the viscoelastic material are the same from one layer to another and the characteristics of the rigid material vary from one layer to another, or alternatively the characteristics of the rigid material are the same from one rigid layer to another.
The invention also relates to a turbomachine comprising at least one such lever for rotating a variable-pitch stator vane about its pivot. More specifically, it is a gas turbine engine compressor comprising at least one lever such as this for rotating a variable-pitch flow straightener vane about its pivot.
The invention is now described in greater detail with reference to the attached drawings in which:
This disk 10 comprises vanes 11 positioned radially with respect to the axis of the engine 1, and mounted to pivot about radial axes within a casing sector 12. Each one rotates as one, about its radial axis, with a lever 20 positioned on the outside of the casing sector. The levers are able to rotate about these radial axes in synchronism, being driven by an assembly comprising a drive ring 30 surrounding the engine casing and to which each of the levers is fixed by its opposite end to the end that has the radial axle on which it is mounted. An appropriate means of attachment is, for example, a pin 21 passing radially both through the ring 30 and through the end of the lever. One or more actuators, not depicted, instigate the rotational movement of the ring about the engine axis. This movement is transmitted to the levers which pivot simultaneously about radial axes and cause the stator vanes to rotate about these same axes.
Viscoelasticity is a property of a solid or of a liquid which, when deformed, exhibits both viscous and elastic behavior by simultaneously dissipating and storing mechanical energy.
The isotropic or anisotropic elasticity properties of the rigid material of the backing layer 44 are greater than the isotropic or anisotropic properties of the viscoelastic material in the desired thermal and frequency-based operating range. By way of a non-limiting example, the material of the layer 44 may be of the metallic or composite type, and the material of the layer 42 of the rubber, silicone, polymer, glass or epoxy resin type. The material needs to be effective in terms of the dissipation of energy in the expected configuration that corresponds to determined temperature and frequency ranges. It is chosen on the basis of its characteristic shear moduli, expressed in terms of deformation and rate.
According to other embodiments, the laminate comprises several layers 42 of viscoelastic material and several backing layers of rigid material 44, which alternate with one another. The example shown in the figure depicts, non-limitingly, a vibration-damping laminate having three layers 42 of viscoelastic material and three backing layers 44 of rigid material. Depending on the application, the layers of viscoelastic material 42 and the backing layers of rigid material 44 may be of the same sizes or of different sizes. When the laminate comprises several layers 42, these may all have the same mechanical properties or may alternatively have mechanical properties that differ from one layer to another. When the laminate comprises several backing layers 44, these may all have the same mechanical properties or alternatively these may have mechanical properties that differ from one layer to another. The layers 42 and the layers 44 are fixed together preferably by adhesion using a film of adhesive, or by polymerization.
According to another embodiment that has not been depicted, it may be kept pressed against the surface of the lever by mechanical means: for example, by a clamping device on each side of the part 20C, by a mechanical connection (screw/nut, rivet, crimping or the like) passed through the zone 20C of the lever and the laminate, by a preload effect obtained upon fitting by deforming the geometry at rest: fixing the zone 55 to the part 20B using the existing lever connection and having the zone 54 bear with preload against the part 20C of the lever.
The laminate extends over the entire surface of the third zone 20C of the lever. Its trapezoidal shape corresponds to the shape, again trapezoidal, of the third zone 20C of the lever between the first zone 20A and the second zone 20B. In this example, the surface portion to which the laminate is applied occupies the entire third zone. However, according to the vibration-damping requirements, the extent of the surface portion may be smaller than that of the third zone. Furthermore, the thicknesses and the nature of the materials that make up the layers 42 and 44 are determined according to the desired amount of damping.
According to another embodiment that has not been depicted, the laminate 40 is applied not to the upper face of the zone 20C of the lever but to the lower face 20Ci of the zone 20C of the lever 20. According to another embodiment depicted in
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| Number | Date | Country | Kind |
|---|---|---|---|
| 0706431 | Sep 2007 | FR | national |
