Variable stator vane rigging

Abstract

A variable vane mechanism for adjusting the angle of stator vanes in a gas turbine engine is provided. The mechanism includes a circumferentially extending unison ring that is driven circumferentially around a casing by an actuator. The unison ring is connected to the stator vanes via levers such that the angle of the vanes changes with circumferential movement of the unison ring. The unison ring and the casing are each provided with at least one rigging hole in order to set the initial angle of the vanes. At least one of the unison ring and the casing are each provided with at least two rigging holes, so that the initial angle of the vanes can be adjusted by selecting different combinations of rigging holes. This may allow accumulations in tolerances to be compensated for and/or may allow the engine to be tested at different initial vane angles.

Claims

1. A method of setting an angle of a set of variable stator vanes comprising: providing a unison ring that is radially offset from a casing, wherein: the circumferential position of the unison ring is related to the angle of the stator vanes; and each of the unison ring and the casing is provided with at least one rigging hole, and at least one of the unison ring and the casing is provided with at least two rigging holes that are both capable of being aligned with one or more rigging holes of the other of the unison ring and the casing, the method further comprising: moving the unison ring circumferentially relative to the casing so as to align a unison ring rigging hole with a casing rigging hole; and inserting a rigging pin through the aligned rigging holes so as to circumferentially fix the position of the unison ring relative to the casing.

2. A method of setting the angle of a set of variable stator vanes according to claim 1, wherein each of the unison ring and the casing is provided with at least two rigging holes.

3. A method of setting the angle of a set of variable stator vanes according to claim 1 wherein the angle between two neighbouring rigging holes in the unison ring and/or the casing is in the range of from 0.1 degrees and 10 degrees.

4. A method of setting the angle of a set of variable stator vanes according to claim 1, further comprising: measuring the angle of at least one of the stator vanes using an inclinometer; and inserting the pin through the combination of unison ring rigging hole and casing rigging hole for which the measured angle best matches a desired angle.

5. A method of calibrating a set of variable stator vanes comprising: setting the variable stator vanes to a desired angle using the method of claim 1; and with the variable stator vanes set to the desired angle, connecting the unison ring to an actuator (200) using a drive bar (220), the actuator being configured to drive the unison ring in a circumferential direction (50, Y) via the drive bar in use.

6. A method of calibrating a set of variable stator vanes according to claim 5, further comprising selecting the length of the drive bar based on the distance between the actuator and a drive bar location position on the unison ring.

7. A method of assembling a set of variable stator vanes comprising: calibrating the set of variable stator vanes using the method of claim 5; and removing the rigging pin, wherein the variable stator vanes are connected to the unison ring using respective levers such that the angle of the vanes is determined by the circumferential position of the unison ring.

8. A method of manufacturing a gas turbine engine having at least one variable stator vane stage, the method comprising assembling at least one set of variable stator vanes in a variable stator vane stage using the method of claim 7.

9. A variable stator vane stage for a gas turbine engine comprising: a set of variable stator vanes arranged circumferentially within a casing; a unison ring, the unison ring being attached to each variable stator vane via a respective lever such that circumferential movement of the unison ring results in a change in angle of incidence of the stator vanes; and an actuator connected to the unison ring using a drive bar, the actuator being configured to drive the unison ring in the circumferential direction via the drive bar, wherein: each of the unison ring and the casing is provided with at least one rigging hole, and at least one of the unison ring and the casing is provided with at least two rigging holes that are both capable of being aligned with at least one rigging hole of the other of the unison ring and the casing, such that the angle of incidence of the stator vanes can be set during rigging by inserting a rigging pin through the aligned holes.

10. A variable stator vane stage according to claim 9, wherein each of the unison ring and the casing is provided with at least two rigging holes.

11. A variable stator vane stage according to claim 9, wherein the angle between two neighbouring rigging holes in the unison ring and/or the casing is in the range of from 0.1 degrees and 5 degrees.

12. A gas turbine engine comprising at least one variable stator vane stage according to claim 9.

13. A casing for a variable stator vane stage according to claim 9, wherein the casing is provided with at least two rigging holes.

14. A unison ring for a variable stator vane stage according to claim 9, wherein the unison ring is provided with at least two rigging holes.

15. A method of testing a gas turbine engine according to claim 12 comprising: holding a first combination of unison ring and casing rigging holes in alignment using a rigging pin and connecting the unison ring to the actuator using the drive bar; removing the rigging pin so as to allow the unison ring to move circumferentially relative to the casing in a first rigged arrangement; testing the engine performance in the first rigged arrangement; holding a second combination of unison ring and casing rigging holes in alignment using the rigging pin and connecting the unison ring to the actuator using the drive bar; removing the rigging pin so as to allow the unison ring to move circumferentially relative to the casing in a second rigged arrangement; testing the engine performance in the second rigged arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments will now be described by way of example only, with reference to the Figures, in which:

(2) FIG. 1 is a sectional side view of a gas turbine engine on accordance with the present disclosure;

(3) FIG. 2 is a schematic perspective view of part of a variable stator vane arrangement in accordance with an example of the present disclosure;

(4) FIG. 3 is a schematic view showing unison ring rigging holes, casing rigging holes and a rigging pin forming part of a variable stator vane arrangement in accordance with an example of the present disclosure; and

(5) FIG. 4 is a schematic example of a part of a variable stator vane arrangement in accordance with an example of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

(6) With reference to FIG. 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, an intermediate pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, an intermediate pressure turbine 18, a low-pressure turbine 19 and an exhaust nozzle 20. A nacelle 21 generally surrounds the engine 10 and defines both the intake 12 and the exhaust nozzle 20.

(7) The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the intermediate pressure compressor 14 and a second air flow which passes through a bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 14 compresses the air flow directed into it before delivering that air to the high pressure compressor 15 where further compression takes place.

(8) The compressed air exhausted from the high-pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 17, 18, 19 before being exhausted through the nozzle 20 to provide additional propulsive thrust. The high 17, intermediate 18 and low 19 pressure turbines drive respectively the high pressure compressor 15, intermediate pressure compressor 14 and fan 13, each by suitable interconnecting shaft.

(9) At least one of the compressors 14, 15 and the turbines 17, 18, 19 comprise stages having rotor blades in rotor blade rows (labelled 60 by way of example in relation to the intermediate pressure compressor in FIG. 1) and stator vanes in stator vane rows (labelled 70 by way of example in relation to the intermediate pressure compressor in FIG. 1).

(10) Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan. Further, the engine may not comprise a fan 13 and/or associated bypass duct 22 and/or nacelle 21. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as a turbojet or turboprop engine, for example.

(11) The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction 30 (which is aligned with the rotational axis 11), a radial direction 40, and a circumferential direction 50 (shown perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions 30, 40, 50 are mutually perpendicular.

(12) Any one of the stator vane rows 70 in the gas turbine engine 10 may be a variable stator vane (VSV) row. Such a variable stator vane row 70 comprises a variable vane mechanism that allows the angle of the vanes 70 (for example the angle of incidence of the vanes 70) to be adjusted in use. Purely by way of example, the gas turbine engine 10 shown in FIG. 1 has a VSV row at the inlet to the core of the engine in the form of a variable inlet guide vane (VIGV) row 100.

(13) FIG. 2 shows a part of the VSV (or VIGV) row 100 in greater detail, including a variable vane mechanism. The VSV 100 comprises variable stator vanes 150. The angle of the variable stator vanes 150 may be adjusted during use. In order to vary the angle of the stator vanes 150, an actuator 200 may be used, which may be a linear actuator as in the FIG. 2 example. The actuator 200 is connected to a unison ring 110 (which may be referred to as a drive ring 110) via a drive bar 220 that connects to the unison ring 110 via a joint (which may be a hinge) 210. The joint 210 may allow rotation of the unison ring 110 relative to the actuator 200, for example about an axial direction running through the joint. This may be particularly suitable for arrangement having a linear actuator.

(14) Movement of the actuator 200 (which may be, for example, based on a control signal which may in turn be based on an engine operating condition and/or thrust demand) causes the unison ring 110 to rotate about the axial direction 30. In the FIG. 2 example, linear movement X of the actuator 200 is converted into circumferential movement Y of the unison ring 110.

(15) The unison ring 110 has at least one drive pin 120 connected thereto. The drive pin 120 is rigidly connected to the unison ring 110 such that the unison ring 110 and the drive pin 120 move together. The drive pin 120 is connected to a first end 132 of a lever 130. The first end 132 of the lever 130 therefore moves with the drive pin 120, but may rotate relative to it about a longitudinal axis of the drive pin 120.

(16) A second end 134 of the lever 130 may be separated from the first end 132 in a direction that has at least a component (for example a major component) in the axial direction 30. The second end 134 may be spaced from the first end 132 in a substantially axial direction 30. The second end 134 of the lever 130 is connected (for example rigidly connected) to a vane 150. The second end 134 may, for example, be connected to a spindle 140 that extends from a vane 150, as in the FIG. 2 example. The second end 134 of the lever may be rigidly fixed in the axial 30, radial 40 and circumferential 50 directions, but may be rotatable about a radial direction 40, as indicated by the arrow Z in FIG. 2.

(17) Accordingly, the circumferential movement Y of the unison ring 110 (which may be described as rotation about the axial direction 30) may be converted into rotation Z of the vane 150 about a substantially radial direction 40. This may be achieved by the drive pin 120 and the lever 130.

(18) In order to ensure that the VSV arrangement 100 is reliable (for example accurate and/or repeatable) the unison ring 110 must be kept concentric with the rest of the arrangement. In order to achieve this, one or more centralising pins 160 is provided. Each centralising pin 160 is in slidable contact with a guide surface, which may be part of a casing 170 within which the variable vanes 150 are housed. In use, the guide surface remains stationary, and the first end 162 of the centralising pin 160 slides across, and remains in contact with the guide surface. Accordingly, the position (for example at least the radial position) of the unison ring 110 relative to the casing 170 may be determined and/or maintained by the centralising pin 160. The casing 170 may be said to be rigidly attached to and/or an integral part of the gas turbine engine 10. Other arrangements may have alternative mechanisms for keeping the unison ring 110 concentric with the rest of the arrangement.

(19) The unison ring 110 is provided with holes A, B, C, D, which may be through holes A, B, C, D as in the example illustrated in FIG. 2. The casing 170 is also provided with holes 1, 2, 3, 4, 5, which may be through holes or blind holes as in the FIG. 2 example. In the example shown in FIG. 2, the casing 170 is provided with five holes 1, 2, 3, 4, 5 and the unison ring 110 is provided with four holes A, B, C, D, but it will be appreciated that the casing 170 and unison ring 110 may be provided with any suitable number of holes in accordance with the present disclosure.

(20) FIG. 3 is a close-up schematic view of the holes 1, 2, 3, 4, 5 of the casing 170 and the holes A, B, C, D in the unison ring 110, which may be referred to as rigging holes. FIG. 4 is another schematic view, showing the unison ring 110 with the holes A, B, C, D formed therein, along with levers 130 attaching vanes 150 to the unison ring, as described above in relation to FIG. 2. The FIG. 4 schematic is generally a view along a radial direction, but the schematically shown holes 1, 2, 3, 4, 5 in the casing 170 are shown as being offset from the holes A, B, C, D in the unison ring 110 in the axial direction 30 purely to aid the clarity of the Figure. In the embodiment itself, the holes 1, 2, 3, 4, 5 in the casing 170 are axially aligned with the holes A, B, C, D in the unison ring 110.

(21) During set-up, or rigging, of the VSV stage 100, for example, the unison ring 110 may be rotated circumferentially in the direction Y shown in the Figures until one of the holes A, B, C, D in the unison ring 110 is circumferentially aligned with one of the holes 1, 2, 3, 4, 5 of the casing 170. The unison ring 110 may be rotated in any suitable manner, for example by manual rotation. The actuator 200 and the unison ring 110 may be disconnected (or not connected) during this initial set-up in order to allow the unison ring to be rotated into the desired position. In FIG. 2, the holes 1 and A are shown as being aligned, and in FIG. 3 the holes 5 and D are shown as being aligned, although any two holes may be aligned by rotating the unison ring 110 to a different position.

(22) The choice of which holes to align may be determined by which combination of aligned holes result in the vanes 150 being set to the desired angle. This desired angle may result from a different combination of rigging holes for different engine builds, for example due to slightly different alignment of components resulting from manufacture and/or assembly tolerances. The angle of the vanes 150 may be determined by any suitable means, for example using an inclinometer 300, as shown by way of example in FIG. 2.

(23) A rigging pin 400 may be used to fix the circumferential position of the unison ring 110 and the casing 170 relative to each other. The rigging pin 400 may prevent the unison ring 110 from being rotated circumferentially. The rigging pin 400 may be passed through (or into, depending on whether the hole is a through hole or a blind hole) the aligned holes, i.e. through one of the holes 1, 2, 3, 4, 5 of the casing 170 and one of the holes A, B, C, D in the unison ring 110. Accordingly, once the desired combination of holes has been decided upon, the unison ring 110 and the casing 170 may be fixed together using the rigging pin 400.

(24) With the rigging pin 400 fixing the unison ring 110 in position, the actuator 200 may be connected to the unison ring 110 using the drive bar 220, as described elsewhere herein.

(25) The distance between the actuator 200 and the fixing position 210 at which the drive bar 220 is fixed to the unison ring 110 may only be known once the combination of rigging holes 1, 2, 3, 4, 5 and holes A, B, C, D has been selected. The length of the drive bar 220 may be determined by this distance, as in the illustrated arrangement. Accordingly, either a bespoke length drive bar 220 may be used depending on the combination of rigging holes chosen, or the drive bar 220 may be adjustable in length, for example by having an adjustment mechanism, which may comprise a screw thread 225 as illustrated in FIG. 2.

(26) After the actuator 200 has been connected to the unison ring 110 using the drive bar 220, the rigging pin 400 may be removed, thereby allowing circumferential rotation of the unison ring 110 in response to movement of the actuator 200. Accordingly, after the rigging pin 400 has been removed, the angle of the vanes 150 in the VSV stage 100 can be altered as normal by the actuator 200, for example in response to different operating conditions (for example different thrust demands) during operation of the gas turbine engine 10.

(27) Any suitable angular spacing between neighbouring holes 1, 2, 3, 4, 5 of the casing 170 and neighbouring holes A, B, C, D in the unison ring 110 may be chosen, as set out elsewhere herein. In any arrangement according to the present disclosure, the angular spacing between neighbouring holes 1, 2, 3, 4, 5 of the casing 170 may be different to the angular spacing between neighbouring holes A, B, C, D in the unison ring 110, as illustrated by way of example in the FIGS. 3 and 4 arrangements. This may allow a greater number of angular positions to be provided and/or a smaller angular gap between combinations of holes for a given number of casing rigging holes 1, 2, 3, 4, 5 and unison ring rigging holes A, B, C, D.

(28) As noted elsewhere herein, the combination of casing rigging holes 1, 2, 3, 4, 5 and unison ring rigging holes A, B, C, D may be selected in order to achieve a desired angle of the vanes 150 during initial set-up, or rigging, of the VSV stage 100. Additionally or alternatively, the arrangements and/or methods described and/or claimed herein may be used during testing and/or development of an engine in order to measure and/or understand the performance of such an engine with the vanes 150 rigged to various different initial angles using different combinations of casing rigging holes 1, 2, 3, 4, 5 and unison ring rigging holes A, B, C, D.

(29) It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.