GB2471843A

GB2471843A - Variable geometry aerofoil arrangement

Info

Publication number: GB2471843A
Application number: GB0912135A
Authority: GB
Inventors: Peter Allford
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2009-07-13
Filing date: 2009-07-13
Publication date: 2011-01-19
Also published as: GB0912135D0

Abstract

A variable geometry aerofoil assembly for a gas turbine comprises an aerofoil structure 12 having fist and second connecting means 25, 28 on an end face 24 thereof, and a support structure having first and second relatively rotatable portions 16, 18. The first connecting means 25 provides a pivotal connection with one of the portions 16, 18, and the second connecting means 28 provides a pivotal and sliding connection with the other portion 16, 18, so that the aerofoil structure 12 orientation is altered by relative rotation of the first and second portions 16, 18 of the support structure. The connecting means 25, 28 may be pins provided on the aerofoil structure 12 or support structure, with complimentary openings 26, 23 provided on the other of the aerofoil structure 12 or support structure. The opening 23 for the second connecting pin may be an axially extending slot or channel. An intermediate member 30 may be provided between the second connecting pin 28 and the slot or channel 23. The connecting means 25, 28 may be provided on radially inner or outer end faces of the aerofoil structure 12.

Description

A VARIABLE GEOMETRY AEROFOIL STRUCTURE

This invention relates to a variable vane activator and particularly but not exclusively relates to a variable vane actuator for a gas turbine engine.

The rotatable sections of a gas turbine engine typically comprise annular arrays of large fan blade rotors and smaller compressor and turbine rotor blades, the blades normally being intersected with annular arrays of static aerodynamic guide vanes (commonly referred to as stator vanes) . Each set of rotor blades and stator vanes is referred to as a stage. The stator vanes ensure the gas impinges on the rotor at the correct angle. The whole assembly is contained within a fan casing.

Variable inlet guide vanes and variable stator vanes (that is vanes, the pitch of which can be changed during operation of the fan unit) are employed upstream of and within the compressor to ensure that the gas flows at the optimum angle. A variable pitch blade is desirable as the efficiency of the rotor, which is of fixed pitch, can be optimised at different rotational speeds by altering the angle which gas approaches the rotating blade.

Variable inlet guide vanes and variable stator vanes conventionally pivot about spindles provided at both ends of the vane. The vanes are connected to a lever which is pivotably attached to a unison ring mounted around the periphery of the casing. The unison ring is moved circumferentially by small incremental amounts by a hydraulic ram, operable by some suitable means. Hence the pitch of the vane may be altered by operating the hydraulic ram.

The system as described above is considerably less suitable for vanes having a combination of wide chord and a pivot at the leading edge position. Levers for such vanes are likely to increase in length in order to be consistent with maintaining a manageable mechanical effort for vane turning. Unison ring circumferential and axial displacements are also increased as a result of a longer lever. Long levers are also required to be more substantial in construction particularly for large vane angular movements in order to avoid buckling. Such levers add weight to the gas turbine, which is undesirable in a jet engine application.

The present invention therefore seeks to address this issue.

According to a first aspect of the present invention there is provided a variable geometry aerofoil assembly for a gas turbine, the variable geometry aerofoil assembly comprising: an aerofoil structure comprising first and second connecting means provided on an end face of the aerofoil structure; and a support structure configured to support the aerofoil structure; the support structure comprising a first portion and a second portion, the first portion being rotatable with respect to the second portion, wherein the first connecting means provides a pivotable connection to one of the first and second portions of the support structure and the second connecting means provides a pivotable and slidable connection to the other of the first and second portions of the support structure, such that the aerofoil structure orientation is altered by rotation of the first portion of the support structure with respect to the second portion.

The first connecting means may comprise a first pin.

Said one of the first and second portions of the support structure may comprise a first opening for cooperation with the first pin.

The first connecting means may comprise a first opening. Said one of the first and second portions of the support structure may comprise a first pin for cooperation with the first opening.

The second connecting means may comprise a second pin.

Said other of the first and second portions of the support structure may comprise a channel for cooperation with the second pin.

The second connecting means may comprise a channel.

Said other of the first and second portions of the support structure may comprise a second pin for cooperation with the channel.

The variable geometry aerofoil assembly may further comprise an intermediate member disposed between the channel and the second pin. The intermediate member may comprise a second opening for cooperation with the second pin and the intermediate member may be slidably disposed in the channel.

The end face of the aerofoil structure may face radially outwards. The end face of the aerofoil structure may face radially inwards. The variable geometry aerofoil assembly described above may be applied to both the inwardly and outwardly facing end faces of the aerofoil structure. In other words the variable geometry aerofoil assembly may be applied at the interface between a casing and the aerofoil structure and/or a hub and the aerofoil structure.

The first and second portions of the support structure may comprise first and second rings respectively. A bearing assembly may be provided between the first and second rings.

A turbomachine may comprise a variable geometry aerofoil assembly as described above. A gas turbine may comprise a variable geometry aerofoil assembly as described above.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-Figure 1 shows a partially cutaway perspective view of a variable geometry aerofoil structure according to an example of the present invention; Figure 2 shows a partial axial section of a variable geometry aerofoil structure with a superimposed end on view of an aerofoil structure according to an example of the present invention; Figure 3a shows the orientation of an aerofoil structure in an end on view for a range of settings and Figure 3b shows the corresponding settings in a radial plane; Figure 4 shows a perspective view of a trailing edge of an aerofoil structure according to an example of the present invention; Figure 5a shows a radial section of a support structure according to an example of the present invention and Figure 5b shows a sectional view corresponding to section XX shown in Figure 5a; and Figure 6 shows an axial section of a variable inlet guide vane according to an example of the present invention.

With reference to Figure 1, a variable geometry aerofoil assembly 10 for a gas turbine engine, according to an embodiment of the present invention, comprises an aerofoil structure 12, 12' (for example an inlet guide vane or stator vane) and a support structure 14 (for example a casing structure) configured to support the aerofoil structure. Whilst Figure 1 shows only a single aerofoil structure 12, a plurality of aerofoil structures may be disposed about the centre line of the gas turbine engine in a radial fashion.

The support structure 14 comprises a first portion 16 and a second portion 18, the first portion being rotatable with respect to the second portion. An actuation means for rotating the first portion 16 with respect to the second portion 18 may comprise a hydraulically driven gear arrangement (not shown) . The aerofoil structure 12 comprises first and second connecting means 20, 22 provided on an end face 24 of the aerofoil structure. The first connecting means 20 is provided towards the leading edge of the aerofoil structure 12, whilst the second connecting means 22 is provided towards the trailing edge of the aerofoil structure 12. A third connecting means 21 is provided at a radially innermost point of the aerofoil structure (i.e. at the hub) The first connecting means 20 provides a pivotable connection to the first portion 16 of the support structure 14. By contrast, the second connecting means 22 provides a pivotable and slidable connection to the second portion 18 of the support structure 14. This pivotable and slidable connection is provided by virtue of the second connecting means pivoting and sliding in an internal track or channel 23 provided in the second portion 18 of the support structure 14. The variable geometry aerofoil assembly 10 therefore enables the orientation of the aerofoil structure 12 to be altered by rotation of the first portion of the support structure with respect to the second portion.

Figure 1 shows the aerofoil structure in a first open position 12 and the aerofoil structure in a second closed position 12' (shown dotted in Figure 1) With reference to Figure 2, the support structure 14 and the end face 24 have a substantially spherical profile, thereby ensuring a constant geometric relationship throughout the angular movement of the aerofoil structure 12. The first, second and third connecting means 20, 22, 21 comprise pivot points and the pivot points of the first and third connecting means are positioned along a common radial axis. Furthermore, the centrelines for the pivot points of the first, second and third connecting means converge at the engine centreline. In the example shown, the aerofoil structure 12 has a true chord of 235mm at the radially outermost edge.

Referring still to Figure 2, the first connecting means comprises a first pin 25 and the first portion 16 of the support structure 14 comprises a first opening 26 for cooperation with the first pin 25. In the specific example shown the first connecting means comprises a bolt passed through a bush in the movable first portion such that the aerofoil structure may rotate about the bush. In an alternative arrangement, the first connecting means may comprise the first opening and the first portion of the support structure may comprise the first pin for cooperation with the first opening. A similar arrangement is provided for the third connecting means 21 at the radially innermost point of the aerofoil structure 12.

Furthermore, the second connecting means 22 comprises an integral protruding second pin 28 and the second portion 18 of the support structure 14 comprises the channel 23 for cooperation with the second pin 28. The variable geometry aerofoil assembly 10 further comprises an intermediate member 30 disposed between the channel 23 and the second pin 28. The intermediate member 30 comprises a second opening 32 for cooperation with the second pin 28, such that the aerofoil structure 12 may pivot with respect to the intermediate member 30. Furthermore, the intermediate member comprises a substantially spherical bushing, which is slidably disposed in the integrally machined channel 23.

The channel 23 has substantially straight walled sides and the intermediate member 30 has corresponding straight edges which maintain the intermediate member in a sliding relationship with respect to the channel 23.

In an alternative arrangement, the second connecting means may comprise the channel and the second portion of the support structure may comprise the second pin for cooperation with the channel.

Also shown in Figure 2 is a bearing assembly 34 provided between the first and second portions 16, 18 of the support structure 14. The bearing assembly 34 permits the first portion 16 to rotate with respect to the second portion 18. Further details of the bearing assembly are shown in Figures 5a and 5b.

Superimposed onto Figure 2 is an end on schematic view of the aerofoil structure in the open and closed positions 12, 12' . This end on view shows how the first connecting means moves with the first portion 16 in a circumferential direction from the open position 20 to the closed position 20' . By contrast, the second connecting means moves in a substantially axial direction in the channel 23 from the open position 22 to the closed position 22' . The net result is a change in the setting angle (or stagger angle) of the aerofoil structure from the open position to the closed position. In an alternative arrangement the channel 23 may be disposed at an angle to the axial direction, such that the second connecting means moves in an axial and circumferential direction.

With reference to Figures 3a and 3b, a line diagram shows the angular movement of the aerofoil structure for a range of rotations of the first portion. Figure 3a corresponds to the superimposed end on view shown in Figure 2 and is a view of Figure 3b shown in the direction of the arrow denoted A. Figure 3b shows the corresponding range of setting angles in the radial plane. In particular, Figure 3b shows the circumferential movement of the first connecting means 20 about the engine centreline 36.

With reference to Figure 4, the second pin 28 of the second connecting means 22 is an integrally mounted pin, which extends radially outwards from the rear aerofoil structure outer edge and close to the trailing edge. The aerofoil structure may comprise local thickening 38 (also known as tree trunking') at the outer trailing edge in order to enhance structural integrity at the second pin position.

With reference to Figure 5a, the first and second portions are located together via the bearing assembly 34.

As shown in Figure 5a, the first and second portions 16, 18 of the support structure 14 overlap in an axial sense and a plurality of ball bearings 40 are provided in races between the first and second portions. The bearing assembly may further comprise a plurality of spacer balls 42 disposed between the ball bearings 40. The bearing assembly may be in the form of a wire race bearing as depicted in Figure 5a with inside and outside wires 44 and 46 respectively. The bearing assembly further comprises a filler portion 48, provided in a gap in the circumference of the second portion 18, which enables the balls 40, 42 to be fed into the bearing. Figure 5b is a view of the filler portion 48 corresponding to section XX shown in Figure 5a. The filler portion 48 is secured to the second portion of the support structure 14 by a bolt 50.

An advantage of the present invention is that unison rings and the associated levers are not required.

Furthermore, a reduced force is required to actuate the variable geometry aerofoil assembly and a reduced radial height is required above the support structure.

The present invention may potentially be used for all wide chord variable stator applications and also variable stator vanes of lesser chord, but where space constraints make difficult, or preclude, a unison ring/lever system.

In particular, an ideal application for this invention is a wide chord Variable Inlet Guide Vane (VIGV) as shown in Figure 6.

Claims

Claims 1. A variable geometry aerofoil assembly for a gas turbine, the variable geometry aerofoil structure comprising: an aerofoil structure comprising first and second connecting means provided on an end face of the aerofoil structure; and a support structure configured to support the aerofoil structure; the support structure comprising a first portion and a second portion, the first portion being rotatable with respect to the second portion, wherein the first connecting means provides a pivotable connection to one of the first and second portions of the support structure and the second connecting means provides a pivotable and slidable connection to the other of the first and second portions of the support structure, such that the aerofoil structure orientation is altered by rotation of the first portion of the support structure with respect to the second portion.
2. A variable geometry aerofoil assembly according to claim 1, wherein the first connecting means comprises a first pin and said one of the first and second portions of the support structure comprises a first opening for cooperation with the first pin.
3. A variable geometry aerofoil assembly according to claim 1, wherein the first connecting means comprises a first opening and said one of the first and second portions of the support structure comprises a first pin for cooperation with the first opening.
4. A variable geometry aerofoil assembly according to any preceding claim, wherein the second connecting means comprises a second pin and said other of the first and second portions of the support structure comprises a channel for cooperation with the second pin.
5. A variable geometry aerofoil assembly according to any one of claims 1 to 3, wherein the second connecting means comprises a channel and said other of the first and second portions of the support structure comprises a second pin for cooperation with the channel.
6. A variable geometry aerofoil assembly according to claim 4 or 5, wherein the variable geometry aerofoil assembly further comprises an intermediate member disposed between the channel and the second pin, and wherein the intermediate member comprises a second opening for cooperation with the second pin and the intermediate member is slidably disposed in the channel.
7. A variable geometry aerofoil assembly according to any preceding claim, wherein the end face of the aerofoil structure faces radially outwards.
8. A variable geometry aerofoil assembly according to any one of claims 1 to 6, wherein the end face of the aerofoil structure faces radially inwards.
9. A variable geometry aerofoil assembly according to any preceding claim, wherein the first and second portions of the support structure comprise first and second rings respectively.
10. A variable geometry aerofoil assembly according to claim 9, wherein a bearing assembly is provided between the first and second rings.
11. A turbomachine comprising a variable geometry aerofoil assembly as claimed in any one of claims 1 to 10.
12. A gas turbine comprising a variable geometry aerofoil assembly as claimed in any one of claims 1 to 10.
13. A variable geometry aerofoil assembly, substantially as described herein, with reference to and as shown in the accompanying drawings.