GAS TURBINE ENGINE HEATSHIELD

Abstract

A gas turbine engine is provided for an aircraft. The engine includes an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor. The engine further includes core casings surrounding the engine core. The engine further includes one or more engine accessories mounted adjacent to the core casings. The engine further includes a self-supporting heatshield positioned between the one or more engine accessories and the core casings. The heatshield is formed of ceramic matrix composite material.

Claims

1. A gas turbine engine for an aircraft, the engine including: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; core casings surrounding the engine core; and one or more engine accessories mounted adjacent to the core casings; wherein the engine further includes a self-supporting heatshield positioned between the one or more engine accessories and the core casings, the heatshield being formed of ceramic matrix composite material.

2. A gas turbine engine according to claim 1, wherein the one or more engine accessories are mounted vertically beneath the core cowl.

3. A gas turbine engine according to claim 1, wherein the heatshield is formed as a corrugated sheet.

4. A gas turbine engine according to claim 1, wherein the one or more engine accessories include an engine accessory gearbox driven by a take-off from the core shaft.

5. A gas turbine engine according to claim 4, wherein the engine accessory gearbox includes a train of spur gears which transfer the drive to other engine accessories, the spur gears being arranged in a line and having axes of rotation which extend perpendicularly to the principal rotation axis of the engine.

6. A gas turbine engine according to claim 5, wherein the train of spur gears is mounted along a central spine member, the other engine accessories projecting from opposite sides of the spine member and the heatshield being supported along a top surface of the spine member.

7. A gas turbine engine according to claim 1, further including an aerodynamic cowl which surrounds the engine core, the core casings and the one or more engine accessories.

8. A gas turbine engine according to claim 1, further including a propulsive fan located upstream of the engine core, the fan generating a core airflow which enters the core engine and a bypass airflow which enters a bypass duct surrounding the engine core.

9. A gas turbine engine according to claim 8, further including a power gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft.

Description

DESCRIPTION OF THE DRAWINGS

[0052] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0053] FIG. 1 is a sectional side view of a gas turbine engine;

[0054] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0055] FIG. 3 is a partially cut-away view of a power gearbox for a gas turbine engine;

[0056] FIG. 4 shows schematically another sectional side view of a gas turbine engine having an accessory gearbox and other accessories mounted adjacent to the core casings, with ventilation flows while the engine is running indicated by dashed arrowed lines;

[0057] FIG. 5 shows schematically a heatshield for the accessory gearbox and other accessories;

[0058] FIG. 6 shows schematically a variant heatshield for the accessory gearbox and other accessories; and

[0059] FIG. 7 shows schematically a further variant heatshield.

DETAILED DESCRIPTION

[0060] 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 power gearbox 30.

[0061] 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 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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 a 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 30 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.

[0067] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of power gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0068] Optionally, the power gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0069] 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, 22 meaning that the flow through the bypass duct 22 has its own nozzle that is separate to and radially outside the core engine 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.

[0070] 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.

[0071] FIG. 4 shows schematically another sectional side view of the gas turbine engine 10. An engine zone is bounded on a radially outer side by an aerodynamic inner cowl 46 which forms the inner wall of the bypass duct 22, and on an inner side by core casings 44 of the engine core 11. Within the zone, an accessory gearbox 40 driven by a take-off (such as a radial drive shaft) from the core shaft 26 is mounted adjacent to and vertically beneath the core casings, along with other accessories 42 driven by the gearbox 40. The other accessories 42 may include any one or more of a power generator, a fuel pump, an oil pump, a hydraulic pump, and an engine starter motor. To protect the gearbox 40 and other accessories 42 from the high temperatures of the engine core 11, a heatshield 48 is positioned between the gearbox 40 and accessories 42,

[0072] As shown in more detail in FIG. 5, the engine accessory gearbox 40 has a front end that receives the drive from the drive shaft 26 and has a train of spur gears which transfer the drive to the other engine accessories 42. These spur gears are arranged in a line along a central spine member 52, with the engine accessories 42 projecting from opposite sides of the spine member 52. The central spine member 52 extends substantially parallel to the engine axis 9 with the rotation axes of the spur gears perpendicular to the engine axis, and the engine accessory gearbox 40 is thus in contrast with a more conventional circumferentially extending accessory gearbox arrangement.

[0073] The heatshield 48 is conveniently attached to an upper surface of the spine member 52. It is formed as a corrugated sheet that conforms broadly to the contours of the upper surface of the assembly of the gearbox 40, accessories 42 and spine member 52. More particularly, the heatshield 48 extends laterally to either side of the spine member 52 to cover top surfaces of the gearbox 40 and accessories 42. It is self-supporting, with the corrugations helping to stiffen and strengthen the sheet. Conveniently, the heatshield 48 is formed of CMC material, which provides good thermal and mechanical properties for this application. By forming the heatshield 48 as a self-supporting sheet, which is typically of uniform thickness, it is possible to avoid complex-shaped stress-raising features that would otherwise be associated with stiffening and/or support structures.

[0074] When the engine is running, ventilation flows (indicated by arrowed dashed lines in FIG. 4) are diverted into the engine zone from the bypass air flowing through the bypass duct 22. These ventilation flows enter the zone through a forward inlet vent 56 at the front of the zone, and an inlet vent 58 formed in a services conduit 60 which extends across the bypass duct 22 from a position beneath the gearbox 40 and accessories 42. The ventilation flows exit the zone at a rearward outlet vent 62, the ventilation flows being maintained by a pressure differential between the inlet and outlet vents. The combination of the thermal insulation provided by the heatshield 48 and the ventilation flows prevents the gearbox 40 and accessories 42 from overheating.

[0075] FIG. 6 shows schematically a variant heatshield for the accessory gearbox and other accessories. To prevent any aviation liquid (such as fuel, lubricating oil or hydraulic liquid from a leaking pipe or component) accumulating on the heatshield 48, and in particular pooling in the depressions formed by the corrugations and thereby constituting a fire hazard, the variant heatshield has drainage holes 50 formed at the bottoms of the depressions. In this way, liquid can drain downwards through the holes, and ultimately can exit the engine zone through a further drainage hole formed in the lowest point of the inner cowl 46. In addition, liquid can drain off to the rear of the heatshield along a central gutter 54 formed where the heatshield attaches to the spine member 52.

[0076] Although not shown in FIGS. 5 and 6, other holes can be formed in the heatshield 48, e.g. to allow routing of services through the heatshield, or to accommodate upwardly projecting features of the gearbox 40 and accessories 42.

[0077] FIG. 7 shows schematically a further variant heatshield for the accessory gearbox and other accessories. In this variant, the heatshield is formed by CMC panels 56 mounted in a metal frame 58. This simplifies the manufacture of the CMC, while still allowing the heatshield to conform broadly to the contours of the upper surface of the assembly of the gearbox 40, accessories 42 and spine member 52.

[0078] 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.