Abstract
There is disclosed a bearing chamber apparatus for a gas turbine engine comprising: a housing defining a bearing chamber for containing lubricant, the housing comprising an inner wall facing the bearing chamber; and wherein the inner wall comprises an oleophobic surface. A method is also disclosed, comprising: providing a bearing chamber apparatus for a gas turbine engine, the bearing chamber apparatus comprising a housing defining a bearing chamber for containing lubricant, the housing comprising an inner wall facing the bearing chamber, forming an oleophobic surface on the inner wall. A gas turbine engine for an aircraft comprising a bearing chamber apparatus is also disclosed.
Claims
1. A bearing chamber apparatus (50) for a gas turbine engine comprising: a housing (60) defining a bearing chamber (58) for containing lubricant, the housing (60) comprising an inner wall (62) facing the bearing chamber (58); wherein the inner wall (62) comprises an oleophobic surface.
2. A bearing chamber apparatus (50) according to claim 1, wherein the oleophobic surface comprises a surface topography which increases the oleophobicity of the surface.
3. A bearing chamber apparatus (50) according to claim 2, wherein the surface topography comprises conical frusta (72) and/or inverted conical frusta (64).
4. A bearing chamber apparatus (50) according to claim 2, wherein the surface topography comprises cylinders (80).
5. A bearing chamber apparatus (50) according to claim 2, wherein the surface topography comprises continuous (88) and/or non-continuous gratings.
6. A bearing chamber apparatus (50) according to claim 2, wherein the surface topography comprises staggered non-continuous gratings.
7. A bearing chamber apparatus (50) according to claim 2, wherein the surface topography comprises re-entrant structures.
8. A bearing chamber apparatus (50) according to claim 2, wherein the inner wall (62) comprises a first region (100) and a second region (102), the surface topography being different in the first region (100) and the second region (102) such that the first region (100) is more oleophobic than the second region (102).
9. A bearing chamber apparatus (50) according to claim 8, wherein the first region (100) is oleophobic and the second region (102) is oleophilic.
10. A bearing chamber apparatus (50) according to claim 8, wherein the first region (100) is proximate to a seal (104), and the second region (102) is distant from the seal (104).
11. A method comprising: providing (300, 400) a bearing chamber apparatus (50) for a gas turbine engine, the bearing chamber (58) apparatus comprising a housing (60) defining a bearing chamber (58) for containing lubricant, the housing (60) comprising an inner wall (62) facing the bearing chamber (58), forming (302, 304, 306, 308, 402, 404, 406, 408) an oleophobic surface on the inner wall (62).
12. A method according to claim 11, wherein the step of forming an oleophobic surface on the inner wall (62) comprises forming (302, 306, 402, 406) a surface topography on the inner wall (62).
13. A method according to claim 11 wherein the method comprises additive manufacture (302, 306, 402, 406) of the oleophobic surface.
14. A method according to claim 11, wherein the step (302, 306, 400, 402, 406) of providing a bearing chamber apparatus (50) comprises additive manufacture (300) of the bearing chamber (58).
15. A method according to claim 11, wherein the step (302, 306, 400, 402, 406) of providing a bearing chamber apparatus (50) comprises providing (400) a pre-made bearing chamber (58).
16. A gas turbine engine (10) for an aircraft comprising: an engine core (11) comprising a turbine (19), a compressor (14), and a core shaft (26) connecting the turbine to the compressor; a fan (23) located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox (30) that receives an input from the core shaft (26) and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, and a bearing chamber apparatus (50) in accordance with claim 1 above.
17. The gas turbine engine according to claim 16, wherein: the turbine is a first turbine (19), the compressor is a first compressor (14), and the core shaft is a first core shaft (26); the engine core further comprises a second turbine (17), a second compressor (15), and a second core shaft (27) connecting the second turbine to the second compressor; and the second turbine, second compressor, and second core shaft are arranged to rotate at a higher rotational speed than the first core shaft.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] Embodiments will now be described by way of example only, with reference to the Figures, in which:
[0052] FIG. 1 is a sectional side view of a gas turbine engine;
[0053] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;
[0054] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;
[0055] FIG. 4 is a cross-sectional view of a bearing apparatus for a gas turbine engine;
[0056] FIG. 5 is a schematic view of a liquid drop on a solid surface;
[0057] FIGS. 6a-6l show various surface topographies for an inner wall of a housing of a bearing apparatus;
[0058] FIG. 7 is a schematic view of a re-entrant structure;
[0059] FIGS. 8a-8b show a surface coating applied to the inner wall;
[0060] FIG. 9 shows a variation in surface topography across the inner wall;
[0061] FIG. 10 shows a method of manufacturing a bearing chamber apparatus, and forming an oleophobic surface on the inner wall of a housing of a bearing chamber of the bearing chamber apparatus; and
[0062] FIG. 11 shows a method of providing a bearing chamber apparatus, and forming an oleophobic surface on the inner wall of a housing of a bearing chamber of the bearing chamber apparatus.
DETAILED DESCRIPTION
[0063] 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
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).
[0072] 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.
[0073] 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.
[0074] Referring back to FIG. 1, a bearing arrangement 50 is shown in a gas turbine engine 10. The bearing arrangement 50 in this example is configured to allow rotation between the high pressure shaft 27 and the intermediate (or low) pressure shaft 26, but it should be understood that the bearing arrangement 50 could be utilised elsewhere in the engine 10. Turning to FIG. 4, the bearing arrangement 50 comprises a roller bearing 52 arranged between the high pressure shaft 27 and the intermediate pressure shaft 26. The roller bearing 52 comprises an outer race 54 which is attached to the high pressure shaft 27, an inner race 56 which is attached to the low pressure shaft 26, and a plurality of rollers 57. It will be understood that the bearing arrangement 50 could be located in any part of the engine where a bearing is required. The bearing arrangement 50 further comprises a bearing chamber 58 in which lubricant is contained, so as to lubricate the bearing 52. The bearing chamber 58 is defined by a housing 60, which has an inner wall 62 facing the bearing chamber 58. The inner wall 62 comprises an oleophobic surface.
[0075] In general, it will be understood that when a drop of liquid 51 is in contact with a solid 53, as shown in FIG. 5, an apparent contact angle A is defined as the angle (measured through the liquid) between the apparent solid surface and a tangent to the liquid drop where it meets the solid surface. It will further be understood that an oleophobic surface comprises a surface on which an oil (or lubricant) droplet will have an apparent contact angle of greater than 90, and that as the contact angle increases, the surface can be said to be increasing in oleophobicity. Factors which affect the apparent contact angle include, but are not limited to, the surface energy of the solid, the surface energy (or tension) of the liquid, and the roughness of the solid surface.
[0076] In one embodiment, the oleophobic surface comprises a surface topography which causes the inner wall 62 to repel lubricant.
[0077] Various embodiments of the surface topography are shown in FIGS. 6a-d. Each of the embodiments comprises an array of regular repeating units, each of which projects from the surface of the inner wall 62.
[0078] In a first embodiment, shown in FIG. 6a, the surface topography comprises a repeating unit comprising an inverted conical frustum 64. The repeating unit is repeated across the surface of the inner wall 62, in this example in two orthogonal directions. The inverted conical frustum 64 comprises a circular upper surface 66 at a distal portion thereof which is parallel to the surface of the inner wall 62, and a circular lower boundary 68 at the proximal portion, where the inverted conical frustum 64 is contiguous with the inner wall 62. The upper surface 66 has a larger diameter than the lower boundary 68, such that a peripheral surface or side wall 70 of the frustum 64 slopes inwardly towards the lower boundary 68. The side wall 70 of the frustum 64 forms an angle of over 90 with surface of the inner wall 62 and the upper surface 66, such that an overhang, or re-entrant angle (or re-entrant structure) is formed. An example re-entrant structure is shown in FIG. 7. A re-entrant structure 63 comprises a structure in which a normal of a peripheral surface 65 of the structure 63 is at an angle between 90-180 to the normal of the general surface plane 67. Relative to the general surface plane 67, a re-entrant structure includes surfaces that are at an angle greater than 90. The perpendicular axis of a re-entrant surface intersects with the general surface plane. The re-entrant angle increases the oleophobic effect of the surface topography.
[0079] In a second embodiment, shown in FIG. 6b, the surface topography comprises a repeating unit comprising a conical frustum 72. The repeating unit is repeated in two directions across the surface of the inner wall 62. The conical frustum 72 comprises a circular upper surface 74 which is parallel to the surface of the inner wall 62, and a circular lower boundary 76 at which the conical frustum 72 is contiguous with the inner wall 62. The upper surface 74 has a smaller diameter than the lower boundary 76, such that a peripheral surface or side wall 78 of the frustum 72 slopes outwardly towards the lower boundary 76. The side wall 78 of the frustum 72 forms an angle of under 90 with surface of the inner wall 62 and the upper surface 74.
[0080] In a third embodiment, shown in FIG. 6c, the surface topography comprises a repeating unit comprising a cylinder (or column) 80. The repeating unit is repeated in two directions across the surface of the inner wall 62. The cylinder 80 comprises a circular upper surface 82 which is parallel to the surface of the inner wall 62, and a circular lower boundary 84 at which the cylinder 80 is contiguous with the inner wall 62. The upper surface 82 and the lower boundary 84 have the same diameter, such that the side wall 86 of the cylinder is perpendicular to the upper surface 82, the lower boundary 84 and the surface of the inner wall 62. The side wall 86 forms an angle of 90 with the surface of the inner wall 62 and the upper surface 82.
[0081] In a fourth embodiment, shown in FIG. 6d, the surface topography comprises a repeating unit comprising a cuboid 88. It will be understood that the cuboid 88 may be a cube. The repeating unit is repeated in one direction across the surface of the inner wall 62. This surface topography may be described as a continuous grating. In other embodiments, the repeating unit may be repeated in two directions across the surface of the inner wall 62, which may be described as fins, or a non-continuous grating. These fins (or non-continuous grating) may be in-line (FIG. 6e) or staggered (FIG. 6f). The cuboid 88 comprises a rectangular upper surface 90 which is parallel to the surface of the inner wall 62, and a rectangular lower boundary 92 at which the cuboid 88 is contiguous with the inner wall 62. The cuboid 88 has two side walls 94, 96 which are perpendicular to the upper surface 90, the lower boundary 92 and the surface of the inner wall 62, such that the side walls 94 form an angle of 90 with the surface of the inner wall 62, and the upper surface 90. In other embodiments, this angle may be lower than 90, so as to form a trapezoidal prism grating 91. The trapezoidal prism grating may be continuous (FIG. 6g), non-continuous in-line (FIG. 6h), or non-continuous staggered (FIG. 6i). In yet further embodiments, the angle may be greater than 90, so as to form an inverted trapezoidal prism grating 93 with a re-entrant angle and increase the oleophobic effect. The inverted trapezoidal prism grating may be continuous (FIG. 6j), non-continuous in-line, (FIG. 6k) or non-continuous staggered (FIG. 6l).
[0082] In addition to the embodiments discussed above, there may be other embodiments in which an angle between an upper surface and a side wall forms a re-entrant angle and increases the oleophobic effect of the surface topography.
[0083] In the embodiments described above, the inner wall 62 comprises an oleophobic surface which comprises a surface topography that causes the inner wall 62 to repel lubricant. In another embodiment, shown in FIG. 8a, the oleophobic surface comprises an applied coating 98 with a low surface energy, such that the inner wall 62 repels lubricant. The applied coating 98 comprises a material with a surface energy that is lower than the surface energy of the lubricant. The applied coating 98 is applied to the inner wall 62 by spraying, painting or spin coating.
[0084] As shown in FIG. 8b, the oleophobic surface may comprise an applied coating 98 and a surface topography as described above, so as to increase the oleophobic effect. Although a grating-type topography is shown in FIG. 6b, it should be understood that any such oleophobic surface topography could be used.
[0085] In a further embodiment, as shown in FIG. 9, which shows an upper half of the bearing chamber apparatus 50 of FIG. 4, the inner wall 62 has a first region 100, proximate to a seal 104 of the bearing chamber 58, and a second region 102, distant from the seal 104. The first region 100 is more oleophobic than the second region 102, such that the contact angle of the lubricant of the surface is greater in the first region 100 than the second region 102.
[0086] In this embodiment, the first region 100 comprises an oleophobic surface, such that the contact angle of lubricant on the surface is greater than 90. The second region 102 comprises an oleophilic surface, such that the contact angle of lubricant on the surface is smaller than 90. In other embodiments, the first region may comprise an oleophobic surface, such that the contact angle of lubricant on the surface is greater than 120 and the second region 102 may also comprise an oleophobic surface, such that the contact angle of lubricant on the surface is greater than 90.
[0087] The oleophobicity of the inner wall 62 decreases gradually between the first region 100 and the second region 102. This means that the lubricant will be repelled away from the area surrounding the seal 104, and towards the second region 102. As a result, there will be less oil coking in the first region 100, which will reduce the amount of coked lubricant getting into the seal 104, resulting in a greater efficiency and/or operational life of the bearing 52.
[0088] Referring now to FIG. 10, a method of manufacturing a bearing chamber apparatus is shown. A design for the bearing chamber apparatus is prepared using Computer Aided Design (CAD) software. At step 300 of the method, the bearing chamber apparatus 50 is additively manufactured using the design prepared by CAD. The next stage of the additive manufacture process can comprise forming an oleophobic surface topography on an inner wall 62 of a housing 60 of the bearing chamber apparatus 50 (step 302), or applying a surface coating 98 to an inner wall 62 of the housing 60 (step 304 or 308). The surface coating 98 comprises a material which has a lower surface energy than the bearing lubricant. The step of applying a surface coating 98 to the inner wall 62 of the housing 60 may optionally be followed by forming an oleophobic surface topography on the inner wall 62 (step 306). As discussed above, the oleophobicity of the inner wall 62 may vary across the inner wall 62.
[0089] Referring now to FIG. 11, an additional method of manufacturing a bearing chamber apparatus is shown. At step 400 of the method, the bearing chamber apparatus 50 is provided, for example a pre-existing bearing chamber of a gas turbine engine which does not comprise an oleophobic surface. A design for an inner wall 62 of the housing 60 is prepared using Computer Aided Design (CAD) software. Additive manufacture is then used to prepare the inner wall 62, in line with the CAD design, so as to form an oleophobic surface topography on the inner wall 62 (step 402), or apply a surface coating 98 to the inner wall 62 (step 404 or 408). The surface coating 98 comprises a material which has a lower surface energy than the bearing lubricant. The step of applying a surface coating 98 to the inner wall 62 may optionally be followed by forming an oleophobic surface topography on the inner wall 62 (step 406). As discussed above, the oleophobicity of the inner wall 62 may vary across the inner wall 62. As such, an oleophobic surface for the inner wall can be retro-fitted to a pre-existing bearing chamber.
[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.
