The invention concerns the field of gas turbine engines, and more particularly gas turbine engine blower casings.
In the case of aircraft engines, a bladed blower disc is situated on the rotor part at the inlet to the engine and precedes the bladed discs of the compressor. This bladed blower disc accelerates the air before entering the compressor stages. This bladed blower disc is liable to receive foreign bodies such as ice, birds or others. Because of this, this bladed disc is liable to deform, to cause an imbalance on the blower support shaft and cyclic loads and vibrations communicated by the blower shaft support bearings to the fixed parts of the turbine engine, to which these support bearings are connected.
To prevent communication of these loads and vibrations, it is known from the application FR 2 752 024 how to fit a so-called “fusible” bearing, that is to say the bearing supporting the blower shaft is connected to the fixed parts of the turbine engine by fairly weak connections so that they break as soon as a certain load is exerted on the blower blades. These weak connections can be screw connections for example. Once the connection is broken, the bladed disc of the blower continues to turn freely, which avoids transmitting forces onto the fixed parts of the turbine engine. However, the axis of rotation of the bladed disc of the blower oscillates about the fixed axis of rotation of the turbine engine. This oscillation causes that of the blades, which then violently touch the blower casing. The latter is thus greatly stressed mechanically, or even torn, during these shocks.
To remedy this, panels adhesively bonded to the interior of the blower casing have been developed, these panels being composed of a Nomex honeycomb structure filled with an abradable material, bonded to a glass cloth, itself bonded to an aluminium honeycomb, the whole being bonded to the blower casing. Such a technology is expensive and repairs must be carried out in specialist workshops, particularly in the case of casings with a specific shape, for example conical.
The present invention aims to improve the situation.
The invention concerns a turbine engine with an axis of rotation comprising a blower casing and a blower with movable blades, a clearance lying between the internal surface of the casing and the free ends of the blades, a bearing of the blower being connected to fixed parts of the turbine engine by connections such that, in the event of a load on the blower blades, these connections break and the axis of rotation of the blower oscillates about the axis of rotation of the turbine engine.
According to a first characteristic of the invention, the casing comprises, bonded to its internal surface and over at least part of the extent of the clearance, a layer of thermoformable foam placed opposite the ends of the blades of the blower, the layer of thermoformable foam being partly covered with a layer of abradable substance, the thickness of the layer of abradable substance being such that the free ends of the blades of the blower do not reach the layer of foam during the normal functioning of the turbine engine, and, in the event of a load on the blower, the free ends of the blades at least partly fragment all the layers of abradable material and thermoformable foam.
Optional characteristics of the turbine engine according to the invention, complementary or in substitution, are set out below:
The following figures non-limitingly illustrate embodiments of the invention:
The drawings contain essentially elements of a certain character. They can therefore not only serve to give a better understanding of the description but also contribute to the definition of the invention, where applicable.
As known to persons skilled in the art,
The bladed blower disc is situated at the inlet to the engine and precedes the bladed discs of the compressor. In
The invention makes it possible to remedy these drawbacks.
As in
Over at least part of the internal wall of the second truncated cone part there is bonded a layer of thermoformable foam 19 by means of a film of adhesive 12. In the example in
In the example in
Other embodiments are possible: for example, the blower casing can consist of a single piece (frustoconical, cylindrical or other) with symmetry of revolution covered on its internal surface with a protective screen consisting of a layer of thermoformable foam, itself partly covered with an abradable substance. As previously, the layers of thermoformable foam and abradable substance, referred to as “large clearance” abradable layers, are placed opposite the ends of the blades. The blower casing has a clearance between its internal surface and the free ends of the blades so as to a stick a certain thickness of layers on the internal surface of the casing, for example around 20 mm. The flow stream is preserved by the fitting, upstream and downstream of the protective layers, of acoustic panels for example.
The protection of the casing, in the case of rupture of the breaking connection of the fusible bearing, is effected by the screen consisting of thermoformable foam and the abradable substance. In this case, the bearings of the blower shaft are no longer connected to the fixed parts of the turbine engine and the axis of rotation of the blower oscillates about the axis of rotation B of the turbine engine. The ends of the blades dig into the screen by fragmentation of material. Advantageously, the presence of the layer of thermoformable foam offers resistance to the removal of material which is less than the layer of abradable substance, which allows the pulverisation of all the “large clearance” abradable layers in the event of rupture of the bearing fuses.
To facilitate the fitting of the layer of thermoformable foam, the latter consists of preformed sectors. By way of example, the layer of thermoformable foam is a layer of polyacrylic imide foam. Also by way of example, the layer of abradable substance can be made from epoxy resin loaded with glass balls, silicone loaded with glass balls or any other material having the abrasion properties of an abradable substance.
More particularly, the layer of abradable substance adheres to the layer of thermoformable foam through its adhesive properties and by diffusion in the cells of the thermoformable foam.
By virtue of these layers of “large clearance” abradable, the casing is not damaged during abnormal functioning (for example in the case of ingestion of a foreign body). The use of thermoformable foam allows simple shaping, the machining being able to be carried out before the shaping, for example for a conical blower casing part, with a changing profile. The layers of “large clearance” abradable can be repaired without equipment requiring a dedicated workshop, which offers a saving in time and money.
The thickness of these layers makes it possible to preserve the flow stream so that, in normal functioning, the ends of the blades of the blower disc do not come into contact with these layers.
The invention is not limited to the embodiments of the fixing device described above, solely by way of example, but encompasses all variants which can be envisaged by a person skilled in the art in the context of the following claims.
The invention does not apply solely to the frustoconical-shaped casing but can also apply in the case of all other casing shapes, for example cylindrical.
Number | Date | Country | Kind |
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0309989 | Aug 2003 | FR | national |