FAN CASE ASSEMBLY FOR A GAS TURBINE ENGINE

Abstract

Aspects of the disclosure regard a fan case assembly for a gas turbine engine, the fan case assembly comprising a fan case having an inner surface, a fan case liner having an outer surface, and a reclosable fastening system attaching the fan case liner to the fan case, the reclosable fastening system comprising two components, a first component being attached to the fan case inner surface and a second component being attached to the fan case liner outer surface.

Claims

1. A fan case assembly for a gas turbine engine, the fan case assembly comprising: a fan case having an inner surface; a fan case liner having an outer surface; and a reclosable fastening system attaching the fan case liner to the fan case, the reclosable fastening system comprising first and second components, the first component being attached to the fan case inner surface and the second component being attached to the fan case liner outer surface; a threaded insert integrated into or connected to the outer surface of the fan case liner, the threaded insert being configured to receive a tool reacting against the fan case and pushing the fan case liner away from the fan case, thereby separating the first and second components of the reclosable fastening system.

2. The fan case assembly of claim 1, wherein the fan case liner is configured to be rotated into position against the fan case.

3. The fan case assembly of claim 2, and further comprising: a front hook of the fan case, the front hook providing a pivot point of the rotation of the fan case liner, and a front flange of the fan case liner, wherein the front flange is configured to be slid over the front hook, and wherein the front hook and the front flange are screwed together after the fan case liner has been rotated into position.

4. The fan case assembly of claim 3, wherein an aft end of the fan case liner is additionally attached to the fan case by a row of fasteners.

5. The fan case assembly of claim 1, wherein the fan case liner is additionally attached to the fan case by at least one row of fasteners.

6. The fan case assembly of claim 1, and further comprising offset pads arranged between the fan case inner surface and the fan case liner outer surface, the offset pads defining a radial distance between the fan case liner and the fan case and setting a radial height of the fan case liner.

7. The fan case assembly of claim 1, wherein the reclosable fastening system is axially located at a center or center region between a front end and an aft end of the fan case liner, or forward of the center.

8. The fan case assembly of claim 1, wherein the first component is bonded to the fan case inner surface and the second component is bonded to the fan case liner outer surface.

9. The fan case assembly of claim 8, wherein the reclosable fastening system is configured such that the bond between the first component and the fan case inner surface and the bond between the second component and the fan case liner outer surface are each stronger than a peel strength provided by the reclosable fastening system required to peel apart the first component and the second component.

10. The fan case assembly of claim 1, wherein the fan case liner is a fan track liner.

11. The fan case assembly of claim 1, wherein the fan case liner is a front acoustic panel or a rear acoustic panel.

12. The fan case assembly of claim 1, wherein the reclosable fastening system is a hook and loop fastening system.

13. The fan case assembly of claim 12, wherein the first component of the hook and loop fastening system attached to the fan case inner surface includes hooks.

14. The fan case assembly of claim 1, wherein the reclosable fastening system is a mushroom head fastening system.

15. The fan case assembly of claim 1, wherein the second component is preapplied to the fan case liner.

16. The fan case assembly of claim 1, wherein the first component and the second component each comprise a linear strip extending in a circumferential direction.

17. The fan case assembly of claim 16, wherein each linear strip extends over a complete circumferential length of the fan case.

18. The fan case assembly of claim 16, wherein the first and second components each comprise several linear strips extending in the circumferential direction, wherein the strips are spaced apart in the circumferential direction.

19. The fan case assembly of claim 16, wherein the first and second component each comprise several linear strips spaced apart in an axial direction.

20. (canceled)

Description

[0068] FIG. 1 is a sectional side view of a gas turbine engine;

[0069] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0070] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0071] FIG. 4 is an embodiment of a fan case to which a reclosable fastening system component is attached;

[0072] FIG. 5 is an embodiment of a fan case assembly comprising a fan case and a fan case liner, wherein components of a reclosable fastening system are attached to a fan case inner surface and a fan case liner outer surface, wherein FIG. 5 depicts a moment of assembly in which the fan case liner is rotated into contact with the fan case;

[0073] FIG. 6 is a view radially outward onto a fan case inner surface, wherein a linear strip of a reclosable fastening system is bonded to the fan case inner surface and extends in the circumferential direction;

[0074] FIG. 7 is a view radially outward onto a fan case inner surface, wherein several spaced apart linear strips of a reclosable fastening system are bonded to the fan case inner surface, each extending in the circumferential direction;

[0075] FIG. 8 is an embodiment of a fan case to which a plurality of axially spaced linear strips are attached;

[0076] FIG. 9 is a detail of a fan case assembly comprising a fan case and a fan case liner connected by means of a reclosable fastening system, wherein a threaded insert is incorporated into the fan track liner to assist removal of the fan track liner by means of a tool;

[0077] FIG. 9a shows an embodiment of the threaded insert of the fan case assembly of FIG. 9; and

[0078] FIG. 10 is an embodiment of a reclosable fastening system implemented as a mushroom head fastening system.

[0079] 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 epicyclical gearbox 30.

[0080] 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 epicyclical gearbox 30 is a reduction gearbox.

[0081] 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 epicyclical 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 process 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.

[0082] 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.

[0083] The epicyclical 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 epicyclical gearbox 30 generally comprise at least three planet gears 32.

[0084] The epicyclical 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 epicyclical gearbox 30 may be used. By way of further example, the epicyclical 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.

[0085] 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.

[0086] 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.

[0087] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0088] 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.

[0089] 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.

[0090] In the context of the present invention, the design of a fan case assembly enclosing a fan is of relevance. It is pointed out that the fan case assembly that will be discussed in the following may be implemented in a geared turbofan engine as discussed with respect to FIGS. 1 to 3 but may generally be implemented in any gas turbine engine. The principles of the present invention are not dependent on a particular kind of gas turbine engine.

[0091] More particularly, a particularly useful application lies with Civil Small and Medium Engines, which may have a fan diameter in the range between 35 to 55″. The rotational speed of the fan of such Civil Small and Medium Engines may be in the range between 5000 and 9000 rpm at Maximum Takeoff Thrust.

[0092] FIG. 4 depicts a fan case 4 circumferentially surrounding a fan (not shown). The fan case 4 may be any fan case implemented in a turbofan engine. It comprises a front end at which it is connected to an engine inlet and an aft end at which it is connected to further structural elements of the gas turbine engine. The fan case 4 comprises an outer surface 41 and an inner surface of 42, wherein the inner surface 42 faces the flow path through the fan. Several liners or panels may be arranged along the inner surface 42, wherein FIG. 4 depicts an area of the fan case 4 which is suitable and configured for attachment of a fan track liner. Further fan case liners such as a front acoustic panel, an ice impact liner and a rear acoustic panel may be connected to the fan case 4 in other axial sections.

[0093] As will be discussed in more detail with respect to FIG. 5, a reclosable fastening system or hook and loop fastening system is implemented to connect a fan track liner to the fan case. A hook and loop fastening system comprises a first component and a second component which interact as is known to the skilled person. The components are typically provided in the form of linear strips, but may in principle have other forms as well.

[0094] In FIG. 4, a first component 61 of hook and loop fastening system is connected to the fan case inner surface 42. The connection is by bonding using an appropriate adhesive. As is schematically depicted in FIG. 4, the first component 61 is featuring hooks 610 but may instead feature loops.

[0095] FIG. 5 shows an embodiment of a fan case assembly, wherein the fan case assembly is depicted in a moment during assembly. The fan case assembly comprises a fan case 4 similar to the fan case of FIG. 4. The fan case assembly further comprises a fan track liner 5 having an outer surface 51 and inner surface 52. The outer surface 51 of the fan track liner 5 may be formed by an outer tray. Generally, a fan track liner is structurally embodied in such a manner that it is suited for receiving fan fragments in the event that a fan blade breaks and for avoiding that they penetrate the engine nacelle in an outward direction. For example, it may comprise a honeycomb core structure which is covered by a composite septum sheet. Further, attached to the inner surface 52 is a layer of abradable material (not shown) in a manner known to the skilled person. Such layer of abradable material minimizes air leakage around the blade tips of the fan. However, in the context of the present invention the exact buildup of the fan track liner is not of relevance and any suitable construction and materials may be implemented.

[0096] The fan case liner 5 is connected to the fan case 4 by means of a hook and loop fastening system 6. The hook and loop fastening system 6 comprises a first component 61 featuring hooks connected to the inner surface 41 of the fan case 4. The hook and loop fastening system 6 further comprises a second component 62 featuring loops connected to the outer surface 51 of the fan track liner 5. Upon touch, the first and second components 61, 62 provide for a connection which is very strong to withstand pulling forces and shear forces and weaker to withstand pealing forces, the latter allowing for an easy disassembly as will be discussed further below.

[0097] For assembly, the fan case liner 5 is rotated against the fan case 4. To this end, the fan case 4 comprises a front hook 43. The front end of the fan track liner 5 comprises a front flange 53. The front flange 53 is slid over the front hook 43, wherein screw holes in the front flange 53 (not shown) and screw holes 430 in the front hook 43 come into alignment. After rotation, the front flange 53 and the front hook 43 are screwed together by means of a nutplate (not shown).

[0098] Further, the fan case liner 5 may be attached to the fan case 4 at the aft end of the fan case liner 5 by means of a row of fasteners such as bolts (not explicitly shown in FIG. 4 but shown and discussed in the embodiment of FIG. 9), thereby eliminating the need for hook and loop between bolt holes to avoid mode in the operating range. This ensures that there is only an axially limited circumferential zone for the reclosable fastening system and improves the leverage to peel the fan case liner 5 out once the aft bolts are removed.

[0099] During rotation, the first component 61 of the fan case 4 and the second component 62 of the fan track liner 5 come into contact and create a firm connection between the fan track liner 5 and the fan case 4. If necessary, a thin sheet of plastic could be placed between the two components 61, 62 during installation. The sheet would prevent the fan case liner 5 from being attached while the fan case liner 5 is placed in proper position. Once the fan case liner 5 is aligned, the sheet is removed and the fan case liner 5 is pressed into place.

[0100] The hook and loop fastening connection comprises a defined radial height 65 which participates in setting the proper height of the fan case liner 5. In addition, offset pads may be provided for proper height setting as will be discussed with respect to FIG. 9.

[0101] The hook and loop fastening system can be implemented based on a wide variety of materials, such as polyester and Teflon. Also, a metallic hook and loop fastening system may be implemented.

[0102] The hook and loop fastening system 6 may be implemented such that the first component 61 comprises hooks 610 as shown in FIG. 4 and the second component 62, accordingly, comprises loops, or vice versa. However, other reclosable fastening systems may be implemented alternatively. FIG. 10 shows an alternative embodiment in which a mushroom head fastening system 6 is implemented comprising identical first and second components 61, 62 each comprising mushroom heads 630. Such mushroom head fastening systems are provided by the company 3M and known as 3M™ Dual Lock™.

[0103] The first and second components 61, 62 may be arranged in the axial direction roughly central (midspan) between the front end and the aft end of the fan case liner 5 (which corresponds to the axial distance between the screw holes 430 and a rear row of bolting). In embodiments, they may be located forward to such central position.

[0104] FIGS. 6 and 7 show two embodiments of the manner in which the first component 61 extends in the circumferential direction along the inner surface 41 of the fan case 4. Both figures hook radially outside onto the inner surface 42 of the fan case 4. The axial direction corresponds to the vertical extension of FIGS. 6 and 7 and the circumferential direction corresponds to the horizontal extension of FIGS. 6 and 7.

[0105] According to FIG. 6, the first component 61 is a linear strip extending in the circumferential direction over the complete circumferential length of the fan case (thus 360°). The linear strip may be an inch wide band. According to FIG. 7, the first component 61 comprises a plurality of linear strips 61-1 to 61-3 each extending in the circumferential direction, wherein the individual strips are spaced apart in the circumferential direction. Accordingly, a continuous or interrupted connection between the fan track liner 5 and the fan case for may be provided for in the circumferential direction.

[0106] Naturally, the second component 62 extends in the same manner and with the same length as the first component 61 on the outer surface of the fan case liner and, accordingly, also comprises continuous or interrupted linear strips extending in the circumferential direction.

[0107] FIGS. 6 and 7 also show bolt holes 45 in the fan case used for bolting the aft end of the fan track liner to the fan case 4.

[0108] FIG. 8 shows an embodiment of the fan case 4, wherein the first component 61 comprises a plurality of linear strips 61-4, 61-5, 61-6 which are spaced apart in the axial direction. This allows to attach the fan track liner to the fan case 4 at a plurality of axial positions. The circumferential extension of the linear strips 61-4, 61-5, 61-6 may be in accordance with FIG. 6 or FIG. 7. Further, the second component 62 of the hook and loop fastening system extends in the same manner and with the same length on the outer surface of the fan case liner and, accordingly, also comprises a plurality of linear strips spaced apart in the axial direction.

[0109] FIG. 9 is an enlarged view of the aft end of a connection between a fan case liner 5 and a fan case 4 by means of a hook and loop fastening system and may represent an example of the aft end connection of the embodiment of FIG. 5. FIG. 9 further comprises details of how to disassemble the hook and loop fastening system.

[0110] More particularly, FIG. 9 depicts the aft end of a fan track liner 5 connected by means of a hook and loop fastening system 6 to a fan case 4 in the manner described before. More particularly, a first component 61 connected to the fan case 4 and a second component to connected to the fan case liner 5 are in reclosable and provide for a hook and loop connection.

[0111] FIG. 9 further shows that the fan track liner 5 forms at its aft end an aft flange 54 which is connected by means of a row of bolts 81 to a structure 44 of the fan case 4.

[0112] Further, the embodiment of FIG. 9 depicts offset pads 91 with closely controlled thickness which are arranged between the outer surface 51 of the fan track liner 5 and the inner surface 42 of the fan case 4. Such offset pads 91 may be pre-attached to the outer surface 51 of the fan case liner 5 by the manufacturer of the fan case liner. They may also be integral into the fan case liner's outer laminate. They serve to exactly define the radial distance between the fan case liner 5 and the fan case 4 and to set the proper radial height of the fan case liner 4. Controlling the radial location of the fan case liner 5 is critical to ensure that the rotor tip clearance is maintained throughout operation. Ensuring a gap between the liner and the case may also allow for threaded device 71 be inserted during disassembly instead of being integral into liner 5.

[0113] FIG. 9 also depicts a blade tip of a fan 23.

[0114] Generally, the hook and loop fastening system 6 may be configured such that the bond between the first component 61 and the fan case inner surface 42 and the bond between the second component 62 and the fan case liner outer surface 51 are each stronger than the peel strength provided by the reclosable fastening system 6 required to peel apart the first component 61 and the second component 62. This allows to conveniently disassemble the fan track liner 5 if damaged and replace it.

[0115] For disassembly, the screws and bolts are removed first. Subsequently, in an embodiment, a wedge of metal or plastic is inserted on the edges of the fan track liner 5 between the liner and casing hook and loop to begin peeling the outer tray of the fan case liner 5 off the casing skin.

[0116] In another embodiment, which is depicted in FIG. 9, a threaded insert 71 is integrated into the fan track liner 5 or temporarily held to the outside surface 51 of the fan track liner 5. FIG. 9a shows an embodiment of such threaded insert 71. Further, access holes 56 are included through the liner inner diameter at each insert location. A tool 72 such as a T-handle tool can be inserted through the access holes 56 and threaded into the threaded insert 71. The tool 72 reacts against the fan case 4 as it is advanced into the threads of insert 71 thus pushing the hook and loop apart. The insert 71 is installed around the periphery of the fan track liner 5 to start peeling the hook and loop apart. The tool 72 can include a plastic tip 721 to avoid marring the fan case 4.

[0117] Accordingly, by threading the tool 72 into the threaded insert 71, the fan case liner 5 is pushed away from the fan case 4 and the components 61, 62 are peeled out of contact. As hook and loop connections are strong in pulling or shear but weaker in peel, such motion is best suited to separate the components 61, 62. However, in normal operation the fan case liner 5 could not be peeled off the fan case 4 as the aft bolts 81 are resisting motion of the fan case liner in the direction of prying.

[0118] While the detailed description referred to the attachment of a fan track liner to a fan case by means of a reclosable fastening system, this is to be understood as exemplary only. A similar attachment may be provided between other fan case liners and a fan case.

[0119] It should be understood that the above description is intended for illustrative purposes only and is not intended to limit the scope of the present disclosure in any way. For example, the above description refers to the attachment of a fan track liner to a fan case by means of a reclosable fastening system. A similar attachment may be provided between other fan case liners and a fan case.

[0120] Also, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. Various features of the various embodiments disclosed herein can be combined in different combinations to create new embodiments within the scope of the present disclosure. In particular, the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein. Any ranges given herein include any and all specific values within the range and any and all sub-ranges within the given range.