1. Field of the Invention
The present invention relates to the field of twin-spool gas turbine engines and, more particularly, to the cooling of a high-pressure turbine disk of a twin-spool gas turbine engine.
2. Description of the Related Art
A twin-spool turbojet with a front fan, for example, comprises a low-pressure spool, termed LP spool, and a high-pressure spool, termed HP spool.
By convention, in the present application, the terms “upstream” and “downstream” are defined with respect to the direction in which the air circulates in the turbojet. Thus, a twin-spool turbojet with a front fan comprises conventionally, from upstream to downstream, a fan, an LP compressor stage, an HP compressor stage, a combustion chamber, an HP turbine stage and an LP turbine stage.
The shaft of the LP spool is guided in its rotation in bearings supported by the fixed structure of the engine whereas the shaft of the HP spool is guided by bearings supported by the LP spool, the shafts of the two spools being concentric.
During the operation of the turbojet, a mixture of air and fuel is burnt in the combustion chamber of the engine in order to create the thrust necessary to move the aircraft on which the turbojet is mounted. After combustion, a flow of gas at a very high temperature circulates in the HP turbine of the turbojet.
The elements of the turbine, in particular the turbine disk of the HP spool, designated hereinafter as HP turbine disk, are subjected to very high temperatures. In order to protect the HP turbine disk, cooling circuits are formed in the engine, in which circuits air, extracted upstream of the HP turbine, circulates, from upstream to downstream in the turbojet, inside the HP turbine disk and outside the LP shaft. The circuit for cooling the HP turbine disk is designated as circuit for cooling the bore of the turbine disk, better known as “circuit bore cooling”.
After having cooled the HP turbine disk, the cooling air passes through a plurality of ventilation openings formed in the journal secured to the HP disk and mounted downstream of the latter, the journal being designated hereinafter as HP journal. The HP journal comprises, inter alia, a ring for the mounting of the bearing 17 making it possible to guide the HP spool on the LP shaft, as represented in FIG. 1.
Still with reference to FIG. 1, the HP journal 10 is fastened by its upstream end to the HP turbine disk 20, the HP turbine disk 20 comprising a radial annular fastening flange 25 coming into contact with a radial annular part 15 of the HP journal 10. The fastening flange 25 of the HP turbine disk 20 is bolted to the HP journal 10 by longitudinal bolts 2.
The ventilation through openings 11 of the HP journal 10, allowing the evacuation of the cooling air flow, are formed downstream of the HP journal part 10 which is bolted to the HP turbine disk 20. In a conventional manner, the ventilation through openings 11 are formed in a frustoconical part 12 of the HP journal 10, which part is flared in the upstream direction and which is highly stressed mechanically in operation.
The ventilation through openings 11 are machined obliquely in the frustoconical part 12 of the HP journal 10. In other words, the ventilation openings 11 are not orthogonal to the surface of the frustoconical part 12 of the HP journal 10. These oblique openings 11 are difficult to machine, the frustoconical part 12 of the HP journal 10 being difficult to access by the machining tools. Furthermore, after machining, the ventilation through openings 11 have sharp edges with a concentration of fatigue stresses which are liable to weaken the HP journal 10 during its operation.