Mitigation of effects of fan blade off in a gas turbine engine

Abstract

A fan is mounted on a fan shaft which constitutes part of a mainline shaft assembly centered for rotation on an engine axis X-X of a gas turbine engine. When in operation, the fan rotates about the engine axis X-X. A stub-shaft is arranged radially outwardly and concentrically with the fan shaft and adjoins an upstream facing face of a bearing sleeve. A fan catcher arm extends from the stub-shaft through the bearing sleeve and joins a fan catcher ring arranged downstream of the bearing sleeve and having an upstream facing face arranged to abut against a downstream facing face of the bearing sleeve in the event of a fan blade-off. Immediately downstream of the fan catcher ring is formed a shaft end which is configured to couple with an axially adjacent end of a low pressure compressor shaft. Immediately downstream of the bearing sleeve is a shaft end configured to connect with a turbine shaft.

Claims

1. A gas turbine engine comprising; a fan mounted for rotation on a fan shaft having an axis of rotation X-X, a stub shaft coaxially arranged with the fan shaft, radially facing surfaces of the stub shaft and fan shaft engaging each other at an end adjacent the fan, a fan catcher assembly comprising one or more fan catcher arms extending from the stub shaft to a fan catcher ring located axially downstream of the fan, the stub-shaft connected to an upstream facing face of a bearing housing and the fan catcher ring having an upstream facing face opposing a downstream facing face of the bearing housing, the catcher arm and fan shaft extending through a central aperture of the bearing housing, wherein, in an extended region from a position upstream of an upstream facing face of the bearing housing to a position downstream of the upstream facing face of the bearing housing, a radial gap between the fan catcher arm and the fan shaft is consistently less than 5 mm.

2. A gas turbine engine as claimed in claim 1 wherein the extended region extends from the stub shaft.

3. A gas turbine engine as claimed in claim 1 wherein the extended region terminates at a downstream end at a position which is closer to the upstream facing face of the bearing housing than to the downstream facing face of the bearing housing.

4. A gas turbine engine as claimed in claim 1 wherein the radial gap is minimised such that, in the event of unbalance in the fan, the fan shaft and fan catcher arm deflect together as if a single body.

5. A gas turbine engine as claimed in claim 1 wherein the radial gap is 4mm or less.

6. A gas turbine engine as claimed in claim 1 wherein the radial gap is 3 mm or less.

7. A gas turbine engine as claimed in claim 1 wherein the radial gap is 2 mm or less.

8. A gas turbine engine as claimed in claim 1 wherein the radial gap is 1 mm or less.

9. A gas turbine engine as claimed in claim 1 wherein complementary contours are provided on opposed radially facing walls of the fan shaft and fan catcher arm in the extended region.

10. A gas turbine engine as claimed in claim 1 wherein the thickness of the fan shaft in a radial dimension is increased in the extended region compared to outside of the extended region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present disclosure will now be further described with reference to the accompanying Figures in which:

(2) FIG. 1 shows a known configuration of the fan end of a turbofan gas turbine engine;

(3) FIG. 2 shows the configuration of FIG. 1 after a fan blade-off event which has led to failure of the fan catcher assembly;

(4) FIG. 3 shows an embodiment of fan and fan catcher arrangement suited to use in a gas turbine engine in accordance with the present disclosure;

(5) FIG. 4 is a sectional side view of a gas turbine engine.

DETAILED DESCRIPTION

(6) FIGS. 1 and 2 have been described above.

(7) In the arrangement of FIG. 3, a fan 31 is mounted on a fan shaft 32 which constitutes part of a mainline shaft assembly centered for rotation on an engine axis X-X. When in operation, the fan 31 rotates about the engine axis X-X. A stub-shaft 33 is arranged radially outwardly and concentrically with the fan shaft 32 and adjoins an upstream facing face of a bearing sleeve 35. A fan catcher arm 34 extends from the stub-shaft 33 through the bearing sleeve 35 and joins a fan catcher ring 36 arranged downstream of the bearing sleeve 35 and having an upstream facing face arranged to abut against a downstream facing face 35b of the bearing sleeve 35 in the event of a fan blade-off. Immediately downstream of the fan catcher ring 36 is formed a shaft end 37 which is threaded to receive a nut (not shown) that holds the shaft onto the fan catcher ring 36. Immediately downstream of the bearing sleeve 35 is threaded 39 for a nut (not shown) to be attached that holds onto the bearing sleeve 35. The mainline shaft assembly constitutes the fan shaft 32, compressor shaft and turbine shaft.

(8) In contrast to the prior known arrangement of FIGS. 1 and 2, from the stub shaft 33 to a position 40 downstream of the upstream facing face 35a of the bearing sleeve 35 radially facing surfaces of the fan catcher arm 34 and fan shaft 32 are closely located over an extended region 41.

(9) In the event of a fan blade-off event, unbalance in the fan results. Due to the close proximity of the fan shaft 32 and fan catcher arm 34 in the extended region 41, the two behave as one component which is considerably stiffer than the fan catcher arm 34 alone. Thus, the fan catcher arm is less prone to flexing and collision with the bearing sleeve 35 under radial loads comparable to radial load R in the arrangement of FIGS. 1 and 2. The risk of fracture of the fan catcher arm is significantly reduced. Risk of consequential damage to engine components downstream (not shown) is thus significantly reduced. Optionally, the stiffness of the fan shaft 32 in the extended region 41 is further increased by thickening 40 of the shaft in a radially inward direction.

(10) FIG. 4 shows an example of gas turbine engine into which the described fan, stub shaft and fan catcher assembly may be employed.

(11) With reference to FIG. 4, a gas turbine engine is generally indicated at 410, having a principal and rotational axis 411. The engine 410 comprises, in axial flow series, an air intake 412, a propulsive fan 413, an intermediate pressure compressor 414, a high-pressure compressor 415, combustion equipment 416, a high-pressure turbine 417, an intermediate pressure turbine 418, a low-pressure turbine 419 and an exhaust nozzle 420. A nacelle 421 generally surrounds the engine 410 and defines both the intake 412 and the exhaust nozzle 420.

(12) The gas turbine engine 410 works in the conventional manner so that air entering the intake 412 is accelerated by the fan 413 to produce two air flows: a first air flow into the intermediate pressure compressor 414 and a second air flow which passes through a bypass duct 422 to provide propulsive thrust. The intermediate pressure compressor 414 compresses the air flow directed into it before delivering that air to the high pressure compressor 415 where further compression takes place.

(13) The compressed air exhausted from the high-pressure compressor 415 is directed into the combustion equipment 416 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 417, 418, 419 before being exhausted through the nozzle 420 to provide additional propulsive thrust. The high 417, intermediate 418 and low 419 pressure turbines drive respectively the high pressure compressor 415, intermediate pressure compressor 414 and fan 413, each by suitable interconnecting shaft.

(14) 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.

(15) 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 scope of the invention as defined by the appended claims. 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.