GB2399865A - Improvements in or relating to control of variable stator vanes in a gas turbine engine - Google Patents

Abstract

Vane actuating apparatus for adjusting the angle of incidence of a set of variable angle vanes in a gas turbine engine comprises a plurality of vane actuator levers each attached at one end to a respective vane and at the other end to an actuator ring. The actuator ring moves the vanes in unison about their respective pivot axes. Each lever has at least two resilient arms spaced apart in the radial direction of the engine for limited radial deflection of the lever at the actuator ring end of the lever due to rotation of the ring about the engine axis during adjustment of the vanes.

Description

- 1 2399865

IMPROVEMENTS IN OR RELATING TO CONTROL OF VARIABLE

STATOR VANES IN A GAS TURBINE ENGINE

This invention concerns improvements in or relating to the control of variable stator vanes and/or inlet guide vanes in a gas turbine engine. In particular the invention concerns improvements to vane actuating apparatus.

In a gas turbine engine having a multi-stage axial compressor the turbine rotor is turned at high speed so that air is continuously induced into the compressor, accelerated by the rotating blades and swept rearwards onto an adjacent row of stator vanes. Each rotor stator stage increases the pressure of the air passing through the stage and at the final stage of a multistage compressor the air pressure may be many times that of the inlet air pressure.

In addition to converting the kinetic energy of the air into pressure the stator vanes also serve to correct the deflection given to the air by the rotor blades and to present the air at the correct angle to the next stage of rotor blades.

As compressor pressure ratios have increased it has become more difficult to ensure that the compressor will operate efficiently over the operational speed range of the engine. This is because the inlet to exit area ratios of the stator vanes required for high pressure operation can result in aerodynamic inefficiency and flow separation at low operational speeds and pressures.

In applications where high pressure ratios are required from a single compressor spool the above problem is preferably overcome by using variable stator vanes. Variable stator vanes permit the angle of incidence of the exiting air onto the rotor blades to be corrected to angles which the rotor blades can tolerate without flow separation.

The use of variable inlet guide vanes and/or variable stator vanes permits the angle of one or more rows of stator vanes in a compressor to be adjusted, while the engine is - 2 running, in accordance with the rotational speed and mass flow of the compressor.

The term variable inlet guide vane (VIGV) used herein refers specifically to vanes in the row of variable vanes at the entry to a compressor. The term variable stator vane (VSV) used herein refers generally to the vanes in the one or more rows of variable vanes in the compressor which may include a VIGV row. The function of such VlGV's or VSV's is to improve the aerodynamic stability of the compressor when it is operating at relatively low rotational speeds at off-design, i.e. non-optimum speed, conditions.

At low speed and mass flow conditions, the variable vanes may be considered to be in a closed position, directing and turning the airflow in the direction of rotation of the rotor blades immediately downstream. This reduces the angle of incidence at entry to the blades and hence the tendency of them to stall. As the rotational speed and mass flow of the compressor increases with increasing engine power, the vanes are moved progressively and in unison towards what may be considered to be an "open" position.

The movement is controlled such that the flow angle of the air leaving the stator vanes continues to provide an acceptable angle of incidence at entry to the downstream row of rotor blades. When the vanes are in the fully "open" position, the angles of all of the stator vanes and rotor blades will typically match the aerodynamic condition at which the compressor has been designed i.e. its "design point". The terms "open" and "closed" used herein are to be construed according to the above definition.

For a VIGV or VSV arrangement to function effectively, it must be geometrically precise, such that the angular positions of the vanes in an individual row (or stage) may be controlled accurately, repeatably and in total unison. To achieve these requirements the vanes and actuating mechanism must be capable of moving freely with low friction.

In a typical arrangement each individual vane in a VIGV row is typically supported in two journal bearings at the radially inner and outer ends of the vane aerofoil section. In contrast, in a typical VSV row, the vanes are usually supported at their radially outer - 3 end only by a single journal bearing arrangement. The journal bearing arrangement permits the vane aerofoil to rotate or pivot about its spanwise axis. This axis is typically radial, or nearly radial, relative to the compressor or engine axis. The angular position of the vane is controlled by an actuating lever, which is attached to a spigot type extension at the radially outer journal end of the vane. The actuating lever of each vane in a row is connected to an actuating ring, also commonly referred to as a unison ring, which is concentric with the row of vanes which it acts upon, and rotates about the compressor's axis of rotation. The unison ring is moved by means of an actuator, which may be controlled by a signal from the engine fuel management and control system. As each vane is rotated between its "closed" and 'open" position, the actuating lever follows an arc of a circle about the spanwise axis of rotation of the vane; in a plane that is substantially tangential to the cylindrical, or generally frustoconcal, casing of the compressor. However, in moving each lever between its "closed" and "open" position, the nominal attachment point of the lever to the unison ring rotates in an arc about the compressor axis. The axes of the two arcs of movement are therefore substantially at right angles to one another. Consequently, without an additional degree of freedom, there would be a conflict of the locus of the end of the vane actuating lever and that of its attachment point to the unison ring. The provision of this additional degree of freedom has resulted in many different designs for VIGV and VSV actuating mechanisms.

In one arrangement the vane actuating levers are located in a spherical type bearing in the actuating ring and are pivotably connected to a vane attachment bracket by a pin to provide a hinge type arrangement. The hinge pin is retained by a split pin. This arrangement is relatively complex and the operation of fastening a split pin to each of the many pins is a time consuming repetitive and laborious task which can be subject to human error. In addition, the split pin can become disconnected due to engine vibration if, by way of non-limiting example, it has been incorrectly fastened.

There is a requirement therefore for a vane actuating arrangement that provides the necessary degrees of freedom between the actuator ring and the vane without the mechanical complexity and assembly constraints of hitherto known arrangements. - 4

According to an aspect of the invention there is provided vane actuating apparatus for adjusting the angle of incidence of a set of variable angle vanes in a gas turbine engine; the apparatus comprising a plurality of vane actuator levers each attached at one end to a respective vane and at the other end to an actuator ring for moving the vanes in unison about their respective pivot axes; each lever having at least two resilient arms spaced apart in the radial direction of the engine for limited radial deflection of the lever at the actuator ring end of the lever due to rotation of the ring about the engine axis during adjustment of the vanes. In this way the lever is relatively stiff in the direction of the load applied by the actuating ring to turn the respective vanes, while in the radial plane, i.e. at right angles to the aforementioned plane, the lever is relatively flexible so that the lever can deflect to accommodate movement of the actuating ring about the engine axis.

In a preferred embodiment the lever comprises a pair of resilient arms having substantially the same radial thickness. In this embodiment the stiffness of the lever in the radial direction is approximately one quarter the stiffness of a lever having only one arm with a thickness dimension equal to that of the combined two arm lever.

In preferred embodiments the resilient arms comprise respective cantilevered beams encastred at the end attached to the respective vanes.

The arms may be arranged substantially parallel or they may be inclined with respect to one another. In embodiments where the arms are inclined the arms may be arranged to provide two sides of a triangular crosssection lever, that is to say a lever having a triangular cross-section in the plane normal to the tangential direction of the engine casing.

In preferred embodiments the arms are joined at their respective ends, and preferably the arms are attached to each other only at their respective ends.

In preferred embodiments the levers are fixed at one end to a respective vane spigot. - 5

The levers may be fixed to the spigots by spline arrangements or by any suitable device capable of providing precise angular location and torque transmission.

Conveniently, the levers are connected at their other end to the actuator ring by an extension pin located in and extending from a spherical bearing connected to the actuator ring. The spherical bearing provides three rotational degrees of freedom for the extension pin. Preferably the extension pin is slidably mounted within the spherical bearing so that a further single degree of freedom in the axial direction of the pin is provided.

In preferred embodiments the lever is pivotable between two extreme positions representing vane open and closed positions. Preferably, the lever is arranged to deflect radially inwards by substantially equal amounts from a mid point position when moved towards either of said extreme positions. In this way it is possible to reduce the applied load between the respective levers and the actuator ring, and thereby reduce the bending stresses generated in the resilient arms during movement of the levers from their mid point position. In one particular embodiment the resilient arms are capable of being deflected radially inwards by 0, 75mm (0.030 inches) or so at the "open" and "closed" positions of the vane, and radially outwards by the same dimension at the mid point position.

In one particular embodiment the vane actuating lever may pivot through an angle of approximately 45 between the "closed" and "open" positions of the vane. The lever effectively hinges through an angle of 2 in the plane of the lever, that is to say the lever deflects as if it were hinged at its end where it is attached to the vane spigot by a conventional hinge pin. This deflection is equivalent to a radial distance in the plane of the actuator ring of approximately 1,5mm (0.060 inches).

The resilient actuator lever according to the invention is particularly suitable for use in arrangements where the axial dimension between the actuating ring and the stator vane spigot is limited and fixed, and also where the radial height dimension in the region of the levers is limited. - 6

The stator vanes may comprise variable inlet guide vanes or variable stator vanes.

The stiffness of the lever in its plane of rotation is substantially the same as a single arm lever having a thickness dimension in the radial direction substantially the same as the combined radial thickness dimensions of the said at least two arms. The stiffness of the lever in the said radial direction is substantially'/. of that of a single arm lever having a thickness dimension in the radiant direction substantially equal to the combined radial thickness dimensions of the said at least two arms.

According to a further aspect of the invention there is provided a vane actuating lever for adjusting the angle of incidence of a variable angle stator vane in a gas turbine engine; the lever comprising a first end for attachment to a respective stator vane and a second end for attachment to a vane actuator ring, the lever having at least two resilient arms spaced apart for limited deflection of the lever in use.

Various embodiments will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which; Figure 1 is an axi-symetric cross-section view of a gas turbine engine compressor stage having a row of variable inlet guide means with a known type of vane actuating arrangement; Figure 2a is a detailed axi-symetric view of a vane actuating arrangement according to an embodiment of the present invention; Figure 2b is a plan view of the vane actuating arrangement of Figure 2a; Figure 3a is a detailed view similar to that of Figure 2a of a vane actuating mechanism according to another embodiment of the invention; Figure 3b is a plan view of the vane actuating mechanism of Figure 3a; Figure 4a is a detailed view similar to Figures 2a and 3a showing a further vane actuating arrangement according to another embodiment of the invention; and, Figure 4b is a plan view of the van actuating mechanism of Figure 4a.

Referring to Figure 1, an axial flow compressor stage 10, which is part of a multistage axial flow compressor in a gas turbine engine, comprises a row of circumferentially spaced variable guide vanes 12 positioned upstream (to the left of the drawing in Figure 1) of a row of circumferentially spaced rotor blades 14. The rotor blades 14 are attached to the rim of a rotor disc 16 which is constrained to rotate about the compressor and engine axis 18 within a compressor casing 20 which surrounds the tips of the rotor blades 14. The stator vanes 12 are pivotally mounted with respect to the casing 20 by radially inner and outer radially extending spigots 22 and 24 which extend at the respective radially inner and outer spanwise ends of the vanes. The inner spigot 22 is rotatably mounted within a journal bearing 26 which is fixed to surrounding engine bearing support structure 28. The radially outer spigot is rotatably mounted within a journal bearing 30 provided within a radially extending boss 32 on the outer side of the compressor casing 20. The spigot 24 is connected to a vane actuating ring 36 which extends coaxially about the engine axis 18 on the outside of the casing 20. The spigot 24 is connected to the actuating ring 26 by means of a lever arm 34 which is secured to the spigot by means of a fastening bolt 38.

The radially inner and outer spigots 22 and 24 are aligned so that they define a spanwise axis of rotation about which the vanes 12 pivot when the actuator ring 36 is rotated about the engine axis 18.

The actuator ring 36 is connected to each of the vanes 12 in the same way so that rotation of the ring 36 causes the vanes to pivot about their respective axis together.

Figures 2a, 2a, 3a, 3b, 4a, and 4b show different embodiments of an improved vane actuating arrangement to that of Figure 1. However for ease of understanding, and - 8 where appropriate, components that are present in the illustrated embodiments of the invention shown in Figures 2 to 4 and also in the known arrangement of Figure 1 are described using the same reference numerals.

Referring to the arrangement of Figures 2a and 2b, a vane actuating arrangement 40 comprises a vane actuating ring 36 which is connected to a radially outer spigot 24 of a variable angle stator vane 12 which is pivotable about its spanwise axis 42. In the arrangement of Figure 2a the vane spigot 24 is located in a spherical bearing 44 located in the compressor casing 20. At its end furthest from the casing 20 the spigot is connected to a vane actuator lever 34 by a spline or other fixing means (not shown), and is retained with respect to the spigot 24 by a retaining bolt 38. At its other end the actuating lever 34 is connected to a pin 46 which is slidably mounted within a spherical bearing 48 on the actuator ring 36.

The pin 46 extends axially in the direction of the engine axis 18 so that the pin can slide within the spherical bearing 48 when the ring 36 is rotated. This additional degree of freedom is complimented by the lever 34 which comprises a pair of resilient arms 34a and 34b. The arms 34a and 34b are spaced apart in the radial direction of the engine over the majority of their length. The arms extend generally in the axial direction of the engine. The radial separation of the resilient arms is substantially constant along their length although the radially outer most arm 34a tapers radially inwards towards the retaining bolt 38 at the vane spigot end of the lever 34.

The resilient arms 34a and 34b provide a degree of flexibility in the radial direction to accommodate movement of the actuator ring 36 as it rotates about the axis 18 in a plane substantially perpendicular to the plane of rotation of the lever 34.

In the arrangement of Figures 2a and 2b the arms are joined together at their respective ends. At the end where they are joined to the pin 46 the arms are bent through 90 such that the lever 34 has a hair pin type structure that has a generally L shaped cross-section in the plane of the drawing. - 9 -

The actuator arrangement 50 shown in Figures 3a and 3b is similar to that of the arrangement of Figures 2a and 2b. However, in Figures 3a and 3b the actuator lever 34 has a generally triangular cross-section in the plane of the drawing of Figure 3a, with the radially outer resilient arm 34a inclined with respect to the radially inner resilient arm 34b.

The actuator arrangement 60 shown in the embodiment of Figures 4a and 4b is similar to that of Figures 3a and 3b in the sense that the radially outer resilient arm 34a is inclined with respect to the radially inner arm 34b which extends substantially parallel to the engine axis 18. In the arrangement of Figures 4a and 4b however, the end of the lever 34 that is connected to the actuator ring 36 is bent over so that a loop 62 is formed such that the loop extends parallel to a radially extending part 64 of the lever between the arms 34a and 34b at the pin location. In this way the pin 46 extends through apertures in both the loop part 62 and the parallel radial part 64 of the triangular cross-section lever.

Although aspects of the invention have been described with reference to the embodiments shown in the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be effected without further inventive skill and effort. For example, the actuator lever arms 34 may comprise more than two resilient arms that are spaced apart in the radial direction of the engine axis. The resilient arms may have different bending stiffnesses. In addition the resilient arms may be designed in such a way that they have sufficient flexibility and resilience to deflect under high load conditions, for example due to compressor surge without undergoing permanent distortion. -

Claims (16)

1 Vane actuating apparatus for adjusting the angle of incidence of a set of variable angle vanes in a gas turbine engine; the apparatus comprising a plurality of vane actuator levers each attached at one end to a respective vane and at the other end to an actuator ring for moving the vanes in unison about their respective pivot axes; each lever having at least two resilient arms spaced apart in the radial direction of the engine for limited radial deflection of the lever at the actuator ring end of the lever due to rotation of the ring about the engine axis during adjustment of the vanes.

2 Apparatus as claimed in Claim 1 wherein the said arms are arranged substantially parallel.

3 Apparatus as claimed in Claim 1 wherein the said arms are inclined with respect to one another.

4 Apparatus as claimed in Claim 3 wherein the arms are arranged to provide two sides of a triangular cross-section lever.

Apparatus as claimed in any preceding claim wherein the said arms are joined at their respective ends.

6 Apparatus as claimed in any preceding claim wherein the lever is fixed at one end to a respective vane spigot.

7 Apparatus as claimed in any preceding claim wherein the lever is connected to the said actuator ring by an extension pin located in and extending from a spherical bearing connected to the actuator ring.

8 Apparatus as claimed in any preceding claim wherein the lever is pivotable - 11 between two extreme positions representing vane open and closed positions and wherein the lever is arranged to deflect radially inwards by substantially equal amounts from a neutral mid point position when moved towards either of said extreme positions.

9 Apparatus as claimed in any preceding claim wherein the stator vanes comprise! a set of variable inlet guide vanes or a set of variable stator vanes.

Apparatus as claimed in any preceding claim wherein the stiffness of the lever in its plane of rotation is substantially the same as a single arm lever having a thickness dimension in the radial direction substantially the same as the combined radial thickness dimensions of the said at least two arms.

11 Apparatus as claimed in any preceding claim wherein the stiffness of the lever in the said radial direction is substantially / of that of a single arm lever having a thickness dimension in the radiant direction substantially equal to the combined radial thickness dimensions of the said at least two arms.

12 Apparatus as claimed in any preceding claim comprising a pair of resilient arms.

13 Apparatus as claimed in any preceding claim wherein the arms are of substantially the same thickness in the said radial direction.

14 A vane actuating lever for adjusting the angle of incidence of a variable angle stator vane in a gas turbine engine; the lever comprising a first end for attachment to a respective stator vane and a second end for attachment to a vane actuator ring, the lever having at least two resilient arms spaced apart for limited deflection of the lever in use.

Vane actuating apparatus substantially as hereinbefore described and with reference to Figures 2a, 2b, 3a, 3b, 4a and 4b of the accompanying drawings. - 12

16 A vane actuating lever substantially as hereinbefore described and with reference to Figures 2a, 2b, 3a, 3b, 4a and 4b of the accompanying drawings.