WINDAGE SHIELD

Abstract

A fan rotor module for a gas turbine engine, the fan rotor module comprising a drive arm, a fan disc and a windage shield attached at one or more points to a rear portion of the fan disc, wherein the fan rotor module comprises at least one balancing weight disposed at one or more of the points where the windage shield is attached to the rear portion of the fan disc.

Claims

1. A fan rotor module for a gas turbine engine, the fan rotor module comprising a drive arm, a fan disc and a windage shield attached at one or more points to a rear portion of the fan disc, wherein the fan rotor module comprises at least one balancing weight disposed at one or more of the points where the windage shield is attached to the rear portion of the fan disc.

2. The fan rotor module of claim 1, wherein one or more balancing weights are disposed at each of the points where the windage shield is attached to the rear portion of the fan disc.

3. The fan rotor module of claim 1, wherein the balancing weights each comprise one or more discrete bodies.

4. The fan rotor module of claim 3, wherein each discrete body has a known mass.

5. The fan rotor module of claim 1, wherein the windage shield is attached to the rear portion of the fan disc by at least one mechanical fixing means.

6. The fan rotor module of claim 5, wherein one or more of the mechanical fixing means comprises a nut and a bolt.

7. The fan rotor module of claim 6, wherein one or more balancing weights each comprise one or more washers disposed on the bolt(s).

8. The fan rotor module of claim 1, wherein the drive arm is a forward facing drive arm or a rearward facing drive arm.

9. A gas turbine engine including the fan rotor module of claim 1.

10. An aircraft including the gas turbine engine of claim 9.

11. A method of rear-plane balancing of a fan rotor module for a gas turbine engine, the fan rotor module having a drive arm, a fan disc and a windage shield attached at one or more points to a rear portion of the fan disc, the method comprising: applying at least one balancing weight at one or more of the points where the windage shield is attached to the rear portion of the fan disc.

12. The method of claim 11, further comprising applying one or more balancing weights at each of the points where the windage shield is attached to the rear portion of the fan disc.

13. The method of claim 11, wherein the balancing weights each comprise one or more discrete bodies.

14. The method of claim 13, wherein the balancing weights are varied by varying the number of discrete bodies.

15. The method of claim 11, wherein the windage shield is attached to the rear portion of the fan disc by at least one mechanical fixing means.

16. The method of claim 15, wherein one or more of the mechanical fixing means comprises a nut and a bolt.

17. The method of claim 16, wherein one or more balancing weights each comprise one or more washers disposed on the bolt(s).

18. The method of claim 10, wherein the drive arm is a forward facing drive arm or a rearward facing drive arm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0056] FIG. 1 is a sectional side view of a gas turbine engine;

[0057] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0058] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0059] FIG. 4 shows an arrangement of a part of a gas turbine engine comprising a fan rotor module;

[0060] FIG. 5 shows an example of a windage shield mounted on a fan disc; and

[0061] FIG. 6 shows another example of a windage shield mounted on a fan disc.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0062] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

[0063] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. 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 is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the core exhaust nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0064] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to precess around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0065] Note that the terms low pressure turbine and low pressure compressor as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the low pressure turbine and low pressure compressor referred to herein may alternatively be known as the intermediate pressure turbine and intermediate pressure compressor. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0066] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed invention. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0067] The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0068] It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

[0069] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0070] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0071] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 18 meaning that the flow through the bypass duct 22 has its own nozzle that is separate to and radially outside the core exhaust nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0072] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0073] FIG. 4 shows a conventional arrangement of a part of a gas turbine engine comprising a fan rotor module. The fan rotor module comprises a fan disc 100, a plurality of fan blades 105, a plurality of annulus fillers 110, a windage shield 115, a support ring 120, and a drive arm 125 connected to the fan disc 100 at a first end and to a curvic joint 130 at a second end. The windage shield 115 is mounted on a rear portion of the fan disc 100, disposed axially rearward of the annulus fillers 110. The windage shield 115 is connected to the fan disc 100 via a nut 135 and a bolt 140. In the arrangement shown, the drive arm 125 is rearward facing. The fan disc 100 is balanced in two planes (i.e., a frontal plane of the fan disc 100 and a rear plane of the fan disc 100). The fan disc 100 is balanced in the frontal plane by a first balancing weight or weights attached to an inner diameter of the support ring 120, outlined by a dashed circle A. The fan disc 100 is balanced in the rear plane by a second balancing weight or weights attached to an inner diameter of the curvic joint 130, outlined by a dashed circle B. Balancing weights (i.e. first and second balancing weights) are applied at both forward and rearward locations (i.e., the frontal plane and the rear plane) of the fan 23 (FIGS. 1 and 2) of the gas turbine engine 10 (FIGS. 1 and 2) to evenly distribute the mass of the fan rotor module (including the fan disc 100, fan blades 105, annulus fillers 110, windage shield 115, support ring 120 and other relevant components associated with the fan rotor module) about the axis of rotation 9 (FIGS. 1 and 2) of the fan disc 100, commonly referred to as balancing the fan rotor module. The fan rotor module is balanced to correct, reduce or minimise any harmful out-of-balance vibrational effects which may be caused by an uneven distribution of mass (i.e., an imbalanced fan rotor module) about the axis of rotation 9 of the fan disc 100.

[0074] FIG. 5 shows a conventional arrangement of a windage shield 115 mounted on a fan disc 100. The windage shield 115 is mounted on a rear portion of the fan disc 100. A shield portion 115A of the windage shield 115 extends axially rearward and radially outward from the fan disc 100. The fan disc 100 comprises disc posts 145 extending radially outward. Although not shown in FIG. 5, a space or gap is positioned between adjacent disc posts 145. The role of the disc posts 145 is to correctly locate fan blades in the spaces between adjacent pairs of disc posts 145 when fan blades are mounted on the fan disc 100. An attachment flange 150 extends radially outward from the disc posts 145 at a rear portion of the fan disc 100. The windage shield 115 is connected to the fan disc 100 at the attachment flange 150 using a nut 135 and a bolt 140. A head 155 of the bolt 140 is counter sunk into a rear surface of the windage shield 115.

[0075] FIG. 6 shows a windage shield 115 in accordance with an embodiment of the disclosure mounted on a fan disc 100. The windage shield 115 is mounted on a rear portion of the fan disc 100. A shield portion 115A of the windage shield 115 extends axially rearward and radially outward from the fan disc 100. The fan disc 100 comprises disc posts 145. An attachment flange 150 extends radially outward from the disc posts 145 at a rear portion of the fan disc 100.

[0076] The windage shield 115 is connected to the fan disc 100 at the attachment flange 150 using a nut 135 and a bolt 140. A balancing weight in the form of a cup washer 160 is located on the bolt 140 and is held securely between the attachment flange 150 and the nut 135. A head 155 of the bolt 140 is counter sunk into a rear surface of the windage shield 115.

[0077] Attaching a balancing weight at the attachment flange 150 where the windage shield 115 is attached to a rear portion of the fan disc 100 is convenient as doing so makes use of an existing attachment point in a gas turbine engine. It is therefore not necessary to design and manufacture or incorporate a new attachment point in the gas turbine engine simply for the purpose of attaching balancing weights to correct, reduce or minimise imbalance of the fan disc 100. Attaching a balancing weight at one or more points where a windage shield is attached to a rear portion of a fan disc may be effective for gas turbine engines with a forward facing drive arm where there is no convenient location for rear plane balancing of a fan disc.

[0078] Attaching a balancing weight at one or more points where a windage shield is attached to a rear portion of a fan disc means that the balancing weight is also further radially outward of the axis of rotation of the fan disc, in comparison to a conventional arrangement (such as that shown in FIG. 4) where a rear plane balancing weight is located on an inner diameter of a curvic joint 130. An equivalent balancing effect to that achieved in a conventional arrangement can therefore be achieved using balancing weights of lower mass located at a greater radial distance from the rotational axis of a fan disc (in comparison to a conventional arrangement).

[0079] In alternative arrangements, one or more balancing weights may be disposed at any location at which a windage shield is attached to a rear portion of a fan disc. For example, for arrangements in which a windage shield is attached to a rear portion of a fan disc at a plurality of points, one or more balancing weights may be disposed at one or more of the plurality of points.

[0080] A windage shield may be attached to a rear portion of a fan disc by at least one mechanical fixing means. In the embodiment of FIG. 6, the mechanical fixing means comprises a nut 135 and a bolt 140. In alternative arrangements, the mechanical fixing means may be one or more rivets. The windage shield may be attached to the rear portion of the fan disc by any suitable means.

[0081] In the embodiment shown in FIG. 6, the balancing weight is a cup washer 160, attached to the fan disc 100 via the nut 135 and the bolt 140 passing through the windage shield 115 and through the attachment flange 150. In alternative arrangements, the balancing weight(s) may comprise one or more different types of washers, e.g. cup washers or disc washers. The balancing weight(s) may alternatively be provided by one or more weighted nuts fastened to the bolt.

[0082] More generally, the balancing weight(s) may be provided as one or more discrete bodies having a known mass. The one or more discrete bodies may comprise a shape or form suitable for simple and convenient attachment via a windage shield attachment point. For example, the balancing weight(s) need not comprise an aperture for location on a bolt securing a windage shield to a rear portion of a fan disc, but may instead be held securely by the compressive force between an attachment flange and a nut fastened to the bolt.

[0083] The balancing weight(s) comprising one or more discrete bodies may allow the mass of the balancing weight(s) to be varied by varying the number of discrete bodies used. The appropriate selection of the balancing weight(s) may depend on a variety of factors, including for example the size of the fan, the size of the fan disc and the radial location (i.e., the distance from the rotational axis of the fan) of the points where the windage shield is attached to a rear portion of the fan disc. By utilising one or more discrete bodies, the balancing weight(s) may be more easily varied to provide the required balancing weight to correct imbalance of a fan disc for a specific fan rotor module of a gas turbine engine. The number of discrete bodies may be varied before or after a windage shield is attached to a rear portion of the fan disc.

[0084] A method of rear plane balancing of a fan rotor module for a gas turbine engine, the fan rotor module comprising a drive arm, a fan disc and a windage shield attached at one or more points to a rear portion of the fan disc, may comprise applying at least one balancing weight at one or more points where the windage shield is attached to the rear portion of the fan disc.

[0085] By attaching balancing weights where the windage shield is attached to the rear portion of the fan disc, existing attachment locations can be made use of. The design and/or manufacture of the fan rotor module need not be altered to include an additional attachment point solely for the purpose of attaching a balancing weight for rear plane balancing of the fan disc. Furthermore, the balancing weights attached at one or more of the points where the windage shield is attached to the rear portion of the fan disc may mean the balancing weights are located further radially outward than the balancing weights of a conventional arrangement (for example, where the balancing weights are located on an inner diameter of a curvic joint attached to a drive arm connecting the curvic joint to the fan disc). The greater radial distance between the balancing weights and the rotational axis of the fan rotor module means that balancing weights of a lower mass may be used to provide the same balancing effect as a conventional arrangement.

[0086] The method may further comprise applying one or more balancing weights at each of the points where the windage shield is attached to the rear portion of the fan disc. The balancing weight(s) may comprise one or more discrete bodies. The balancing weights may therefore be varied by varying the number of discrete bodies in each balancing weight. The balancing weight required may depend on the specific arrangement of the fan rotor module. Being able to vary the balancing weight by utilising a variable number of discrete bodies may therefore enable rapid and/or simple adjustment of the balancing weight required for the specific circumstances.

[0087] The windage shield may be attached to the rear portion by at least one mechanical fixing means. One or more of the mechanical fixing means may comprise a nut and a bolt. The balancing weight(s) may comprise one or more washers disposed on the bolt(s). The washers may be cup washers, or may be disc washers.

[0088] The drive arm of the fan rotor module may be a forward facing drive arm, or may be a rearward facing drive arm.

[0089] The method described above may be effective for fan rotor modules comprising a forward facing drive arm, in which there is no convenient existing location for rear plane balancing of the fan rotor module.

[0090] 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.