GB2376269A

GB2376269A - A gas turbine engine breather outlet

Info

Publication number: GB2376269A
Application number: GB0113967A
Authority: GB
Inventors: Ian Colin Deuchar Care; Michael John Mountney
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2001-06-08
Filing date: 2001-06-08
Publication date: 2002-12-11
Also published as: GB0113967D0

Abstract

A turbofan engine lubrication system, for lubricating a gearbox 38, and bearings 53, comprises a tank 47, and a separator 40, which has a breather outlet 42. The breather outlet 42 comprises a breather duct 44, with an exhaust outlet arranged to discharge oil and air from the separator into a fan duct via at least one passage 58, in at least one of the fan outlet guide vanes of the engine. Discharge from a vane may occur through a plurality of apertures extending through the convex surface of the vane, or via a venturi eductor (70, figure 6).

Description

A GAS TURBINE ENGINE BREATHER OUTLET The present invention relates generally to a breather outlet, particularly to a gearbox breather outlet for an aircraft mounted gas turbine engine.

Aircraft mounted gas turbine engines are usually provided with a gearbox, which is driven by the engine and provides drive for certain engine accessories. Such gearboxes are oil lubricated and are provided with so called"breather"outlets to provide communication between the gearbox interior and the exterior of the engine. This is to ensure that the operation of the gearbox does not result in an air pressure build up within the gearbox casing. Inevitably operation of the gearbox results in severe agitation of the oil within the gearbox to the extent that an oil mist is usually formed. This oil mist can escape through the gearbox breather outlet and so it is common to provide a centrifuge device in the breather to separate out the oil mist before it is ejected from the engine. Unfortunately such devices are not completely effective in capturing all of the oil mist so that some of the oil is inevitably lost through the breather outlet.

The magnitude of the oil loss under these circumstances is not great and does not normally present any problems in the effective operation of the gearbox. However, the oil which is ejected from the breather outlet tends to cause dark coloured stains along the engine nacelle. The problem is particularly acute in the case of engine nacelles which are light coloured.

Such stains are seen as being highly undesirable since they are unsightly and are very difficult and time consuming to remove by normal cleaning methods.

European patent EP0439923B1, published 7 August 1991, describes a breather outlet which attempted to overcome these problems. That breather outlet comprises an aerodynamic mast extending from the exterior surface of the

gas turbine engine nacelle. The mast contains a breather duct having an exhaust outlet and the exhaust outlet is generally rearwardly facing with respect to the operational flow of air over the mast. The exhaust outlet is spaced apart from the engine nacelle to minimise interaction between any efflux from the exhaust outlet and the engine nacelle.

The breather outlet described in EP0439923B reduced the amount of staining of the engine nacelle but has not completely cured the problem.

European patent EP0940338A2, published 8 September 1999, describes a breather outlet which attempted to overcome these problems. That breather outlet comprises an aerodynamic mast extending from the exterior surface of the gas turbine engine nacelle. The mast contains a breather duct having an exhaust outlet, the exhaust outlet is generally rearwardly spacing with respect to the operational flow of air over the mast and the exhaust outlet is spaced apart from the engine nacelle. The exhaust outlet has guide vanes in the breather duct to straighten the oil and airflow. The mast also has vortex generators to minimise interaction between any efflux from the exhaust outlet and the engine nacelle.

The breather outlet described in EP0940338A2 further reduced the amount of staining of the engine nacelle but has not completely cured the problem.

Accordingly the present invention seeks to provide a novel breather outlet which further reduces the above mentioned problems.

Accordingly the present invention provides an aircraft mounted gas turbine engine comprising a gas flow duct defined by a casing and vanes extending radially across the gas flow duct, the gas turbine engine comprising a lubrication system, the lubrication system comprising a breather outlet including a breather duct having exhaust outlet means arranged in at least one of the vanes to

discharge lubricant and air from the lubrication system into the gas flow duct.

Preferably the lubrication system comprises a separator arranged to separate lubricant and air and the breather outlet is interconnected with the separator to discharge lubricant and air from the separator into the gas flow duct.

Preferably the lubrication system is arranged to lubricate a gearbox.

Preferably the gearbox is mounted on the casing.

Preferably the gearbox is arranged to drive accessories.

Preferably the gearbox is arranged to drive the separator.

Preferably the separator is mounted on the casing.

Preferably the at least one vane comprises a leading edge, a trailing edge, a convex surface and a concave surface, the at least one vane has at least one passage extending radially through the vane and at least one aperture to discharge lubricant and air from the lubrication system into the gas flow duct.

Preferably the at least one aperture extends through the convex surface of the at least one vane.

Preferably a plurality of apertures discharge the oil and air into the gas flow duct.

Preferably the plurality of apertures are spaced apart radially and/or spaced apart chordally of the at least one vane.

Preferably the at least one aperture is spaced apart radially from the casing.

Preferably the apertures extend through a low-pressure region of the surface of the at least one vane.

Preferably the at least one vane comprises a first metal sheet, a second metal and a third metal sheet, the first, second and third metal sheets are diffusion bonded together and the second metal sheet has been

superplastically formed between the first and second metal sheets to form the at least one radially extending passage.

Alternatively the at least one vane comprises an eductor, the eductor having an outlet at the trailing edge of the vane, a supply of pressurised fluid is arranged to supply pressurised fluid to the eductor, the at least one radially extending passage being connected to the eductor such that in operation a flow of fluid through the eductor withdraws lubricant and air from the lubrication system through the at least one radially extending passage in the vane and out of the outlet of the eductor.

A supply of pressurised air may be arranged to supply pressurised air to the eductor such that in operation the flow of air from the supply of pressurised air through the eductor withdraws lubricant and air from the lubrication system through the at least one radially extending passage in the vane and out of the outlet of the eductor.

The eductor may comprise an inlet at the leading edge of the at least one vane, the supply of pressurised air comprises a supply of air from the gas flow duct of the gas turbine engine.

The supply of pressurised air may comprise a compressor of the gas turbine engine.

The eductor may be a venturi eductor.

The separator may be a centrifugal separator.

Preferably the gas turbine engine is a turbofan gas turbine engine, the gas flow duct is a fan duct defined by a fan casing and the vanes extending radially across the fan duct, the breather duct having exhaust outlet means arranged in at least one of the vanes to discharge lubricant and air from the lubrication system into the fan duct.

Alternatively the gas turbine engine is a turbojet gas turbine engine, the gas flow duct is a turbine duct defined by a turbine casing and the vanes extending radially across the turbine duct, the breather duct having exhaust outlet

means arranged in at least one of the vanes to discharge lubricant and air from the lubrication system into the turbine duct.

The present invention will be more fully described by way of example with reference to the accompanying drawings in which :- Figure 1 shows a turbofan gas turbine engine having a breather outlet according to the present invention.

Figure 2 is a diagrammatic diagram of the lubrication system of the turbofan gas turbine engine shown in figure 1 Figure 3 is an enlarged cut away view of the breather outlet shown in figure 1.

Figure 4 is an enlarged cross-sectional view of the breather outlet shown in figure 1.

Figure 5 is an enlarged cross-sectional view through part of the breather outlet shown in figures 3 and 4.

Figure 6 is an enlarged cut away view through an alternative breather outlet shown in figure 1.

A turbofan gas turbine engine 10, as shown in figure 1, comprises an intake 12, a fan section 14, a compressor section 16, a combustion section 18, a turbine section 20 and an exhaust nozzle 22. The fan section 14 comprises a fan rotor 24 carrying a plurality of circumferentially spaced, radially outwardly extending fan blades 26. A fan casing 28 encloses the fan blades 26. The fan casing 28 partially defines a fan duct, or bypass duct, 30 and the fan casing is supported from a core casing 32 by a plurality of radially extending fan outlet guide vanes 34. Some of the fan outlet guide vanes 34 are also load bearing struts in addition to their aerodynamic purposes and the remainder of the fan outlet guide vanes 34 are provided for aerodynamic purposes. The operation of the gas turbine engine 10 is quite conventional and this will not be discussed further.

The turbofan gas turbine engine 10 has accessories 36, a gearbox 38 and a separator 40 mounted within the fan

casing 28, as shown in figure 1. The gearbox 38 is arranged to drive the accessories 36 and the separator 40. The separator 40 has a breather outlet 42, which comprises a breather duct 44 and exhaust outlet means 46. The separator 40 forms part of a lubrication system 48.

The lubrication system 48, as shown in figure 2, comprises a lubricant tank 47, pipes 49 and 51 arranged to supply lubricant to bearings 53 and the gearbox 38 respectively, pipes 55 and 57 to return lubricant from the bearings 53 and gearbox 38 respectively to the lubricant tank 47 and vent pipes 59 to prevent over pressurisation of the bearings 53, gearbox 38 and lubricant tank 47. The vent pipes 59 allow air to be removed from the lubrication system 48. The vent pipes 59 supply the air, and some oil, to the separator 40. The separator 40 comprises for example a centrifugal separator, which is arranged to separate lubricant from the air removed from the lubrication system 48. The separator 40 returns the separated lubricant to the lubrication tank 47 via the pipe 61 and discharges air from the lubrication system 48 through the breather outlet 42. However, because the separator 40 is not 100% efficient some lubricant remains in the air and is discharged from the breather outlet 42 with the air as a lubricant and air mist.

The fan outlet guide vanes 34, as shown in figures 3, 4 and 5, comprise a leading edge 50, a trailing edge 52, a convex surface 54 which extends from the leading edge 50 to the trailing edge 52 and a concave surface 56 which extends from the leading edge 50 to the trailing edge 52. One of the fan outlet guide vanes 34A is hollow and has at least one radially extending passage 58. The fan outlet guide vane 34A has a plurality of apertures 60 extending through the convex surface 54 of the fan outlet guide vane 34A to interconnect the at least one passage 58 and the fan duct 30. The apertures 60 are arranged in chordally spaced apart rows and the apertures 60 in each row are radially

spaced apart. The apertures 60 are arranged at a region of the convex surface 54 of the fan outlet guide vane 34A where there is low pressure. The apertures 60 are spaced radially from the fan casing 28.

The fan outlet guide vane 34 comprises first, second and third metal sheets 62,64 and 66 respectively, which are diffusion bonded together. The third sheet 66 has also been superplastically formed to form a warren girder structure between the first and second metal sheets 62 and 64. The at least one passage 58 is formed between the first, second and third metal sheets 62,64 and 66. The passages 58 are interconnected by apertures 68 through the third metal sheet 66.

The at least one radially extending passage 58 through the fan outlet guide vane 34A forms a portion of the breather duct 44 and the apertures 60 form the exhaust outlet means 46.

In operation of the turbofan gas turbine engine 10 an oil and air mist is discharged from the separator 40 through the breather outlet 42. The oil and air mist flows through the radially extending passage 58 of the fan outlet guide vane 34A and is discharged into the fan duct 30 of the turbofan gas turbine engine 10 through the apertures 60 in the convex surface 54 of the fan outlet guide vane 34A.

The apertures 60 are spaced apart from the fan casing 28 to minimise the amount of oil and air mist impinging on the acoustic liners within the fan casing 28.

The advantage of the present invention is that there is no staining to the outer surface of the fan casing nacelle. Additionally there is no requirement for a mast to extend from the outer surface of the fan casing/nacelle. This removes the possibility of the mast causing injury to people. This also reduces the amount of drag, due to the removal of the mast, which produced drag.

An alternative fan outlet guide vane 34B, as shown in figure 6, comprises a leading edge 50, a trailing edge 52,

a convex surface 54 which extends from the leading edge 50 to the trailing edge 52 and a concave surface 56 which extends from the leading edge 52 to the trailing edge 54. The fan outlet guide vanes 34B is hollow and has at least one radially extending passage 58. The fan outlet guide vane 34B has a venturi eductor 70 spaced radially from the fan casing 28 and the core engine.

The venturi eductor 70 comprises in flow series an inlet 72, a convergent portion 74, a throat portion 76, a divergent portion 78 and an outlet 80. The inlet 72 is arranged at the leading edge 50 of the fan outlet guide vane 34B and the outlet 80 is arranged at the trailing edge 52 of the fan outlet guide vane 34B. The radially extending passage 58 is connected to an annular chamber 82 arranged coaxially around the venturi eductor 70. The annular chamber 82 is in turn connected to the flow through the venturi eductor 70 upstream of the throat portion 76.

Optionally a pipe 84 is interconnected to the convergent portion 74 of the venturi eductor 70 to supply a pressurised fluid to the venturi eductor 70. The pipe 84 is connected to a suitable position in the compressor section 16 of the turbofan gas turbine engine 10 via a valve (not shown).

The at least one radially extending passage 58 through the fan outlet guide vane 34B forms a portion of the breather duct 42 and the outlet 80 forms the exhaust outlet means 44.

In operation of the turbofan gas turbine engine 10 oil and air mist is discharged from the separator 40 through the breather outlet 42. The oil and air mist flows through the radially extending passage 58 of the fan outlet guide vane 34B and is discharged into the fan duct 30 of the turbofan gas turbine engine 10 through the outlet 80 of the venturi eductor 70 at the trailing edge 52 of the fan outlet guide vane 34B. The outlet 80 of the venturi eductor 70 is spaced apart from the fan casing 28 to

minimise the amount of oil and air mist impinging on the acoustic liners within the fan casing 28. Air flows from the fan duct 28 into the inlet 72 of the venturi eductor 70 and sequentially through the convergent portion 74, throat portion 76, divergent portion 78 and outlet 80 of the venturi eductor 70. This flow of air through the venturi eductor 70 draws oil and air mist through the at least one radially extending passage 58 and into the venturi eductor 70 to be discharged into the fan duct 30 with the air flowing through the venturi eductor 70. The pipe 84 is used to supply higher pressure air from the compressor section 16 to the venturi eductor 70 when the turbofan gas turbine engine 10 is operating at ground idle, or other operating regimes, when the pressure of the air in the fan duct 30 is insufficient to draw the oil and air mist through the radially extending passage 58.

The advantage of the present invention is that there is no staining to the outer surface of the fan casing nacelle. Additionally there is no requirement for a mast to extend from the outer surface of the fan casing/nacelle.

This removes the possibility of the mast causing injury to people. This also reduces the amount of drag, due to the removal of the mast which produced drag.

Although the invention has been described with reference to a gearbox positioned within the fan casing it is equally possible to have a gearbox positioned on the core engine. Although the invention has been described with reference to the gearbox driving accessories it is equally possible for the gearbox to drive other components, for example the fan. Although the invention has been described with reference to the gearbox driving the separator it is equally possible for an electric motor, a hydraulic motor or an engine shaft to drive the separator.

Although the invention has been described with reference to a turbofan gas turbine engine it is equally possible to apply the invention to a turbojet gas turbine

engine. In this case the breather outlet includes a breather duct having exhaust outlet means in one of the vanes in the turbojet to discharge lubricant and air from the lubrication system into a gas flow duct through the turbojet gas turbine engine. The at least one vane is preferably a turbine outlet guide vane.

Claims

Claims :- 1. An aircraft mounted gas turbine engine comprising a gas flow duct defined by a casing and vanes extending radially across the gas flow duct, the gas turbine engine comprising a lubrication system, the lubrication system comprising a breather outlet including a breather duct having exhaust outlet means arranged in at least one of the vanes to discharge lubricant and air from the lubrication system into the gas flow duct.
2. A gas turbine engine as claimed in claim 1 wherein the lubrication system comprises a separator arranged to separate lubricant and air and the breather outlet is interconnected with the separator to discharge lubricant and air from the separator into the gas flow duct.
3. A gas turbine engine as claimed in claim 1 or claim 2 wherein the lubrication system is arranged to lubricate a gearbox.
4. A gas turbine engine as claimed in claim 3 wherein the gearbox is mounted on the casing.
5. A gas turbine engine as claimed in claim 3 or claim 4 wherein the gearbox is arranged to drive accessories.
6. A gas turbine engine as claimed in claim 3, claim 4 or claim 5 wherein the gearbox is arranged to drive the separator.
7. A gas turbine engine as claimed in any of claims 2 to 6 wherein the separator is mounted on the casing.
8. A gas turbine engine as claimed in any of claims 1 to 7 wherein the at least one vane comprises a leading edge, a trailing edge, a convex surface and a concave surface, the at least one vane has at least one passage extending radially through the vane and at least one aperture to discharge lubricant and air from the lubrication system into the gas flow duct.
9. A gas turbine engine as claimed in claim 8 wherein the at least one aperture extends through the convex surface of the at least one vane.

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10. A gas turbine engine as claimed in claim 8 or claim 9 wherein a plurality of apertures discharge the lubricant and air into the gas flow duct.
11. A gas turbine engine as claimed in claim 10 wherein the plurality of apertures are spaced apart radially and/or spaced apart chordally of the at least one vane.
12. A gas turbine engine as claimed in any of claims 8 to 11 wherein the apertures extend through a low pressure region of the surface of the at least one vane.
13. A gas turbine engine as claimed in claim 8 wherein the at least one vane comprises an eductor, the eductor having an outlet at the trailing edge of the vane, a supply of pressurised fluid is arranged to supply pressurised fluid to the eductor, the at least one radially extending passage being connected to the eductor such that in operation a flow of fluid through the eductor withdraws lubricant and air from the lubrication system through the at least one radially extending passage in the vane and out of the outlet of the eductor.
14. A gas turbine engine as claimed in claim 13 wherein a supply of pressurised air is arranged to supply pressurised air to the eductor such that in operation the flow of air from the supply of pressurised air through the eductor withdraws lubricant and air from the lubrication system through the at least one radially extending passage in the vane and out of the outlet of the eductor.
15. A gas turbine engine as claimed in claim 14 wherein the supply of pressurised air comprises a compressor of the gas turbine engine.
16. A gas turbine engine as claimed in claim 14 or claim 15 wherein the eductor comprises an inlet at the leading edge of the at least one vane, the supply of pressurised air comprises a supply of air from the gas flow duct of the gas turbine engine.
17. A gas turbine engine as claimed in any of claims 13 to 16 wherein the eductor is a venturi eductor.

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18. A gas turbine engine as claimed in any of claims 8 to 17 wherein the at least one aperture is spaced apart radially from the casing.
19. A gas turbine engine as claimed in any of claims 8 to 18 wherein the at least one vane comprises a first metal sheet, a second metal and a third metal sheet, the first, second and third metal sheets are diffusion bonded together and the second metal sheet has been superplastically formed between the first and second metal sheets to form the at least one radially extending passage.
20. A gas turbine engine as claimed in any of claims 2 to 19 wherein the separator is a centrifugal separator.
21. A gas turbine engine as claimed in any of claims 1 to 20 wherein the gas turbine engine is a turbofan gas turbine engine, the gas flow duct is a fan duct defined by a fan casing and the vanes extending radially across the fan duct, the breather duct having exhaust outlet means arranged in at least one of the vanes to discharge lubricant and air from the lubrication system into the fan duct.
22. A gas turbine engine as claimed in any of claims 1 to 20 wherein the gas turbine engine is a turbojet gas turbine engine, the gas flow duct is a turbine duct defined by a turbine casing and the vanes extending radially across the turbine duct, the breather duct having exhaust outlet means arranged in at least one of the vanes to discharge lubricant and air from the lubrication system into the turbine duct.
23. A turbofan gas turbine engine substantially as hereinbefore described with reference to figures 1,2, 3,4 and 5 of the accompanying drawings.
24. A turbofan gas turbine engine substantially as hereinbefore described with reference to figures 1,2 and 6 of the accompanying drawings.