Bladed Rotor Assemblies

Abstract

A bladed rotor assembly in which the gaps between the blades below the platforms are sealed by a plurality of sealing plates the adjacent circumferential ends of which overlap, and which are locked onto the rotor disc by means of a pair of locking wires which engage corresponding half-round grooves in the peripheries of the plates and of the rotor disc.

Description

The present invention relates to locking and sealing devices for retaining the blades of a bladed rotor against axial movement on the rotor, and for sealing the gaps at the roots of the blades.

Arcuate sealing plate segments fitting into grooves in the blade platform and the rotor periphery are known per se, but in most known systems the ends of the plate segments cannot be arranged to touch under all running conditions of an engine due to differential thermal expansion between the plate segments and the rotors, so that gaps form between the ends of adjacent plate segments during some running conditions and high pressure air leaks through the gaps.

Another drawback of known sealing plate segments is that it is usual to assemble them by inserting blades one at a time into peripheral slots in the rotor and feeding a plate around aligned grooves in the blade and rotor. Each plate extends across the width of several blades. The difficulty arises when trying to fit the last plate. In some known constructions the last plate has to be deformed in order to insert it.

Additionally the above-described assembly method cannot be used in a situation where the blades have interlocking shrouds and must all be assembled on the rotor together.

One object of the invention is to provide blades, sealing plates, and a rotor arranged so that all the blades, together with the sealing plate, may be assembled simultaneously onto the rotor periphery.

Another object of the present invention is to provide a bladed rotor assembly in which, in addition, leakage between the sealing plates is substantially eliminated.

According to the present invention there is provided a bladed rotor assembly comprising a plurality of blades having root portions which engage in slots on the radially outer periphery of a rotor, each blade having a platform above the root portion, a plurality of arcuate sealing plate segments forming a complete annular sealing plate which extends between the blade platforms and a portion of the rotor which is disposed radially inwardly of the slots on the periphery thereof, and wherein adjacent circumferential ends of the plate segments overlap circumferentially, and each sealing plate segment has locking elements at its radially outer and inner peripheries which co-operate with adjacent locking elements on the blade platforms and said rotor portion, the locking element at one of said peripheries comprising a circumferential groove and the co-operating adjacent locking element being a corresponding circumferential groove which forms with said circumferential groove a continuous circumferential aperture into which is fitted a locking device which extends around substantially the whole of the circumference of the rotor.

In a preferred construction the radially inner peripheries of the plate segments are formed with half-round grooves which are aligned to cooperate with a similar groove on said rotor portion to receive a locking wire of circular cross-section, and the locking element at the radially outer peripheries of the plate segments comprises a groove in each blade platform which are aligned to form a continuous circumferential aperture to receive said peripheries.

Also in the preferred embodiment two locking wires are used, each of which extends substantially around half the length of the aperture formed by the co-operating grooves in the rotor and the plate, and which are fed into the aperture from recesses in the face of the rotor.

In an alternative form the means for locating the radially outer periphery of the sealing plate may comprise a circumferential groove in each sealing plate segment which are aligned to form a continuous circumferential groove in the periphery of the plate, which engages a continuous circumferential projection on the blade platforms.

The sealing plate may have an axially extending portion on which are disposed labyrinth fins which provide a radial or axial seal with an adjacent static structure.

The assembly may comprise either a turbine or a compressor assembly for a gas turbine engine.

The invention will now be more particularly described, merely by way of example, with reference to the accompanying drawings in which:

FIG. 1 illustrates diagrammatically a gas turbine engine with the turbine casing cut away to show a turbine rotor incorporating the present invention,

FIG. 2 is an enlarged view of part of the disc of the turbine rotor of FIG. 1,

FIG. 3 is a view in the axial direction of the rotor disc of FIG. 2, and

FIG. 4 is a view on the arrow A of FIG. 3 showing only the sealing plate.

Referring now to the drawings, in FIG. 1 there is illustrated a gas turbine engine having compressor means 1, combustion equipment 2, turbine means 3, and a propulsion nozzle 4, all in flow series.

The compressor means and the turbine means both comprise a plurality of rotor stages and stator stages and this invention relates to the rotor stages.

Part of a rotor stage 10 of the turbine means is shown in FIG. 2. The stage consists of a plurality of aerofoil-shaped blades 11 mounted in a ring on the periphery of a rotor disc 12. The means of mounting the blades shown in this example is by conventional fir tree roots 13 which engage with correspondingly-shaped slots extending axially in the radially outer periphery of the turbine disc 12.

Each blade 11 has a platform 15 which is provided with a circumferentially extending, radially inwardly facing groove 16. In the assembly all the grooves become aligned to form a continuous circumferential groove beneath the platforms.

The disc has a circumferentially extending, radially outwardly facing groove 17 at its periphery, at a position disposed radially inwardly of the slots. The grooves 16, and 17 constitute locking element for locking a sealing plate.

A plurality of arcuate sealing plate segments 20 are provided, which extend between the blade platforms and the groove in the disc periphery in order to seal the gaps which exist at the blade roots, i.e., below the platforms against loss of high pressure gases.

The radially outer portions of the plate segments 20 are dimensioned to form locking elements 19 which fit into the grooves 16 in the blade platforms, and at the radially inner portions each plate segment is provided with a locking element in the form of a half-round groove 21 which co-operates with the groove 17, which is also half-round, to form an aperture for accepting a locking wire 22 of circular cross-section.

FIGS. 3 and 4 show the plate segments in position but the blades are left out of these Figures. It can be seen that six plate segments 20 are provided, which together form a complete annular sealing plate. At their adjacent circumferential ends (portions 23), each plate segment is reduced to half thickness so that they can overlap to provide a good seal, while at the same time providing gaps 24 which allow for relative thermal expansion between the disc and the segments.

The locking wire 22 is provided in two pieces, each extending around substantially half of the periphery of the disc. The disc is recessed at two diametrically opposite stations 25 at which the locking wire is fed into the circular aperture formed by the co-operating grooves 17 and 21 on the disc periphery and the plate respectively. One end of each wire is bent radially inwardly to prevent the wire passing too far into the groove, and each wire is sufficiently long to project into the opposite recess and thus each is prevented from coming out.

The main advantage of this type of sealing and locking arrangement is that it can be used with blades which have interlocking shrouds and which must all be assembled simultaneously on the disc. Once the ring of blades has been built up with the shrouds interlocked, the plate segments can be inserted into the groove 16 and the whole ring assembled on the disc. The locking wire, or wires, is then inserted to lock the assembly on the disc. A chamfer is formed on one end of the locking wire to ease the insertion of the wire into the grooves.

Another advantage which springs from this invention is that leakage around the sealing plate can be virtually eliminated.

By making the sealing plate a good fit in the groove 16 the overlapping parts of the sealing plate are pressed firmly together so that there is virtually no leakage across the ends of the sealing plate segments while allowing room for circumferential growth of the segments as they get hot in operation.

In operation, centrifugal force on the sealing plate will urge the radially outer periphery of the plate into contact with the base of the groove 16 beneath the platforms to make a good seal. In addition, centrifugal force acting on the locking wire 22 will urge it radially outwardly into tight engagement with the surface of the groove in the radially inner periphery of the sealing plate to prevent leakage over the top of the wire. And, due to gas forces on the turbine blades, the blades, and hence the sealing plate, are urged rearwardly so that the upstream face of the sealing plate in the groove 16 is brought into tight contact with the side of the groove 16, and the locking wire is urged into tight contact with the downstream surface of the groove 17 in the rotor disc periphery. Therefore there should be no leakage either over the radially outer periphery, under the radially inner periphery or between the circumferential ends of the sealing plate segments.

The leakage path over the outer periphery of the sealing plate can be increased in an alternative construction, by forming a circumferentail groove in the radially outer periphery of the sealing plate and a corresponding circumferential projection on the underside of the platform.

Further alternative constructions are possible within the scope of the invention, for example, the cross-sections of the grooves 16 and 17 can be varied, for example, to square or polygonal. The plate may be recessed by suitable machining, e.g., electrochemical machining to reduce its weight.

Although the above description relates to a turbine assembly, the invention is equally applicable to compressor assemblies, and in one such assembly it is proposed to mount labyrinth fins on an axially extending portion of the sealing plate, which fins may be arranged to provide an axial or radial seal with static structure upstream or downstream of the sealing plate.

Again, the invention is illustrated with reference to an assembly having two locking wires, whereas one could be sufficient.

In addition the locking wire may be in the blade platform and need not necessarily be in the disc. This merely means that the radially outer circumference of the sealing plate should be provided with a half-round groove and a similar half-round groove would be provided in the blade platform.

Claims

We claim:

1. A bladed rotor assembly comprising a plurality of blades having root portions which engage in slots on the radially outer periphery of a rotor, each blade having a platform above the root portion, a plurality of arcuate sealing plate segments forming a complete annular sealing plate which extends between the blade platforms and a portion of the rotor which is disposed radially inwardly of the slots on the periphery thereof, and wherein adjacent circumferential ends of the plate segments overlap circumferentially, and each sealing plate segment has locking elements at its radially outer and inner peripheries which co-operate with adjacent locking elements on the blade platforms and said rotor portion, the locking element at one of said peripheries comprising a circumferential groove and the co-operating adjacent locking element being a corresponding circumferential groove which forms with said circumferential groove a continuous circumferential aperture into which is fitted a locking device which extends around substantially the whole of the circumference of the rotor.

2. A bladed rotor assembly as claimed in claim 1 and in which the radially inner peripheries of the plate segments are formed with half-round grooves which are aligned to co-operate with a similar groove on said rotor portion to receive a locking wire of circular cross-section.

3. A bladed rotor assembly as claimed in claim 1 and in which the locking element at the radially outer peripheries of the plate segments comprises a groove in each blade platform which are aligned to form a continuous circumferential aperture to receive said peripheries.

4. A bladed rotor assembly as claimed in claim 2 and in which two locking wires are used, each of which extends substantially around half the length of the aperture formed by the co-operating grooves in the rotor and the plate.

5. A bladed rotor assembly as claimed in claim 1 and in which the rotor is a turbine rotor of a gas turbine engine.