GB2071776A

GB2071776A - Stator Vane Assembly

Info

Publication number: GB2071776A
Application number: GB8009203A
Authority: GB
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1980-03-19
Filing date: 1980-03-19
Publication date: 1981-09-23

Abstract

The assembly comprises a vane 15 having a radially extending spigot 16 at the innermost end located in a bush 17 which is carried by an inner stator structure 18 to provide frictional damping of torsional vibration of the vane. The bush 17 is mounted on trunnions 19 so that the bush pivots about an axis normal to the radial axis 20 and a spring loaded cam 24 is provided to tilt and hold the bush 17 about the pivotal axis to compensate for wear of the spigot 16, bush 17, or stator structure 18 when gas loads on the vane cease. <IMAGE>

Description

SPECIFICATION Turbomachine Stator Vane Assembly This invention relates to stator vane assemblies of turbo-machines and is particularly concerned with stator vane assemblies having radially extending spigots at the innermost ends of the vanes which locate in fixed structure of the turbomachine to provide frictional damping of torsional vibrations of the vanes.

In a known design of gas turbine engine (the Pegasus engine built by Rolls-Royce Ltd) the stator vane assembly of the low pressure compressor is provided with vanes having radially extending spigots at its innermost end which locates in a bush carried by a stator ring of the engine. In use, gas loads on each vane deflects the vane causing it to bend relative to the radial axis passing through the vane. This imparts a turning moment at the spigot which is reacted by a couple generated by the stator ring in which the bushes locate. The frictional engagement between the spigot, bush, and the stator ring provides frictional damping of the torsional vibration of the vanes about the radial axis through the spigot.

In use, the bending moments on the end spigots causes wear at the axially spaced corners of the bushes, either on the bush as is the case with the stator vanes of the first and second stages of the LP compressor of the Pegasus engine (where the bushes are prevented from rotating about their longitudinal axis), or on the stator ring as in the case with the vanes of the third stage of the Pegasus LP compressor (where the bushes are not prevented from rotating about their longitudinal axis).

The wear is slight but is uneven; at different vanes the wear is greater because of different gas loads on the vane than at other vanes. If the wear becomes excessive it becomes necessary to replace individual bushes or to repair or replace the stator ring. This necessitated stripping the engine and is time consuming and costly. Since the wear is slight, a device which would compensate for wear of spigots or bushes of individual vanes would considerably extend the operational life of the stator vane assembly before replacement of the bushes becomes necessary.

An object of the present invention is to provide means for compensating for the wear between the spigots, the bushes, and the stator structure, individually for each vane.

Furthermore, it is an object of the present invention to provide a mechanism which compensates for wear automatically.

According to the present invention there is provided in a stator assembly, for a turbo machine, of the type comprising a vane having a radially extending spigot at its innermost end located in a bush carried by an inner stator structure of the turbo-machine to provide frictional damping of torsional vibrations of the vane, the improvement comprising, mounting each bush on pivot means carried by the stator structure, the pivotal axis of which extends normal to a radial axis passing through the spigot, and providing an actuator means operable on the bush to tilt it about the pivotal axis to take up wear of the bush when gas loads on the vane cease and to hold it in the tilted position, and a biassing means for urging the actuator means into engagement with the bush.

Preferably the actuator means comprises a cam which either engages the bush directly or indirectly through the intermediary of an arm connected to the bush. The biassing means may be a spring which operates to rotate the cam.

Preferably the pivotal axis of the bush lies parallel to the length of the turbo-machine. Alternatively, the pivotal axis of the bush may lie normal to the chord of the vane.

The present invention will now be described, by way of examples, with reference to the accompanying drawings in which: Figure 1 illustrates, schematically a prior known stator vane of a turbo-machine; Figure 2 illustrates a stator vane of a turbo- - machine constructed in accordance with the present invention and shows a mechanism for compensating for wear of the bush in which the vane locates; Figure 3 is a cross-sectional view of the vane of Figure 2 taken along line AA of Figure 2; and Figure 4 illustrates schematically an alternative mechanism to that shown In Figure 2 for compensating for wear of the bush in which the vane locates.

Referring to Figure 1, there is shown part of a prior known stator vane assembly of a low pressure axial flow compressor of a gas turbine aero-engine. The stator assembly comprises a plurality of vanes 10, (one of which is shown), each having at its innermost end a cylindrical spigot 11 which extends radially. The spigot 11 locates in a bush 1 3 carried by stator structure 14 of the engine. The vane 10 has an outer shroud 12 which is mounted in the compressor casing.

In use gas loads on the vane, represented by the arrow L, causes the vane to be deflected as shown by the chain-dotted line (exaggerated).

This causes the vane to impart a bending moment at the spigot 11 shown by the corner forces, represented by arrows X and Y.

The moment on the bush 1 3 in the stator structure 14 induces wear of the bush 13 and when the gas load ceases, when the engine is shut down, the bush 1 3 becomes slack in the structure 14. The bush 13 is usually an interference fit in the structure 14, and the spigot 11 is a tight fit in the bush 1 3 to provide frictional damping of torsional vibrations of the vane about the radial axis. Therefore, excessive wear of either the spigot, the bush or the structure 14, reduces the damping effect and exacerbates vibrational problems.

The stator assembly of the present invention is illustrated in Figure 2 and comprises a vane 15 which has, at its innermost end, a radially extending cylindrical spigot 1 6 which is located in the bore of a bush 17 carried by fixed structure 1 8 of the engine.

The bush 1 7 is in the form of a rectangular cube, and is located between two spaced annular rings 18 forming part of the static structure of the engine.

Each bush 1 7 is pivotally mounted in the rings 18 by a pivot means in the form of trunnions 19.

The pivotal axis of the trunnions 19 extends normal to the radial axis 20 passing through the spigot 1 6 and lies parallel to the centre line axis of the engine. One of the trunnions 19 has a rectangular projection on to which is secured an arm 21.

The rings 18 are bolted together by means of bolts 22, and spacers 23 mounted on the bolts 22 maintain the spacing between the rings 18. The bolts 22 also carry an actuator means, in the form of a cam 24, which engages the arm 21. The cam 24 is provided with a torsion spring 25 which biasses the cam to rotate into engagement with the arm 21. The cam 24 thereby operates on the bush 1 7 (through the intermediary of the arm) to tilt the bush 1 7 about its pivotal axis to take up wear of the bush 1 7, when the gas loads cease. It will be seen that the cam 24 tilts the bush 1 7 in the opposite direction about the pivot to that caused by the moment of the forces X and Y, and holds the bush in the tilted position.Hence, when the gas loads diminish the bush is prevented from returning to its original position and is held in its tilted position to take up wear of the spigot 16, bush 17, or structure 18.

Referring now to Figure 4, the vane 15 is mounted in a bush 1 7 similar to that shown in Figure 2 and the bush 1 7 pivots on trunnions 19 as shown in Figure 2. The cam 24 however does not operate on the bush 17 through the intermediary of an arm 21 as in Figure 2. Rather, the bush 17 is provided with an arcuate recess 25 into which the cam 24 nestles and the cam 24 operates directly on the bush 1 7 to tilt it about its pivot. Each bush 17 has a second arcuate ciearance recess 26 which ensures that the cam 24a, which operates on an adjacent bush 1 7a does not engage both bushes at the same time.

Claims

1. In a stator assembly, for a turbo-machine, of the type comprising a vane having a radially extending spigot at its innermost end located in a bush carried by an inner stator structure of the turbo-machine to provide frictional damping of torsional vibrations of the vane, the improvement comprising, mounting each bush on pivot means carried by the stator structure, the pivotal axis of which extends normal to a radial axis passing through the spigot, and providing an actuator means operable on the bush to tilt it about the pivotal axis to take up wear of the bush when gas loads on the vane cease and to hold it in the tilted position, and a biassing means for urging the actuator means into engagement with the bush.

2. A stator assembly according to claim 1 wherein the actuator means comprises a cam which engages the bush.

3. A stator assembly according to claim 1 wherein the actuator means is a cam which engages an arm attached to the bush.

4. A stator assembly according to claim 2 or claim 3 wherein the biassing means is a spring which operates to rotate the cam.

5. A stator assembly according to any one of the preceding claims wherein the pivotal axis of the bush lies parallel to the length of the turbomachine.

6. A stator assembly according to any one of claims 1 to 4 wherein the pivotal axis of the bush lies normal to the chord of the vane.

7. A stator assembly substantially as hereindescribed with reference to the accompanying drawings.