Inlet assembly for the aft fan of an aircraft

Abstract

The present invention relates to an inlet assembly for a rear fan of an aircraft. Specifically, the present disclosure is directed to a low-distortion inlet assembly (302) for reducing the swirl distortion of the air flow entering a rear fan (300) mounted to the fuselage (12) of an aircraft (10). Additionally, the inlet assembly (302) includes a plurality of structural members (307) circumferentially mounted at one or more predetermined positions around the fan shaft (312) of the fan (300). More specifically, the predetermined positions have a swirl distortion exceeding a predetermined threshold. Further, the inlet assembly (302) includes at least one air flow conditioning element (315) configured within the inlet (334) to reduce the swirl distortion of the air entering the fan (304).

Description

Technical Field

[0001] The present subject matter generally relates to a rear engine for an aircraft propulsion system, and more particularly to an inlet assembly for a rear fan of a rear engine for reducing swirl distortion of an air flow entering the fan. Background Art

[0002] Conventional commercial aircraft generally include a fuselage, a pair of wings, and a propulsion system that provides thrust. The propulsion system typically includes at least two aircraft engines, such as turbofan engines. Each turbofan engine is mounted to a respective one of the aircraft's wings, such as at a suspended position below the wing, separate from the wing and the fuselage. This configuration allows the turbofan engine to interact with a separate free-stream air flow that is not affected by the wing and / or the fuselage. This configuration can reduce the amount of turbulence within the air entering the inlet of each respective turbofan engine, which has a positive effect on the net propulsion thrust of the aircraft.

[0003] However, drag on an aircraft including turbofan engines also has an impact on the net propulsion thrust of the aircraft. The total amount of drag on the aircraft, including skin friction, form, and induced drag, is generally proportional to the difference between the free-stream velocity of the air approaching the aircraft and the average velocity of the wake downstream of the aircraft due to drag on the aircraft.

[0004] Accordingly, systems have been proposed to counteract the effects of drag and / or improve the efficiency of turbofan engines. For example, some propulsion systems incorporate a boundary layer ingestion system to convey a portion of the relatively slow-moving air that forms, for example, the boundary layer across the fuselage and / or wing, into the turbofan engine upstream of the fan section of the turbofan engine. Although this configuration can improve propulsion efficiency by re-energizing the boundary layer air flow downstream of the aircraft, the relatively slow-moving air flow from the boundary layer entering the turbofan engine generally has a non-uniform or distorted velocity profile. As a result, such a turbofan engine can experience an efficiency loss that minimizes or offsets any benefits of reduced drag on the aircraft.

[0005] In addition, some propulsion systems include an electric-driven rear engine that has a rear fan on the aircraft tail to obtain propulsion benefits by ingesting the fuselage boundary layer. During operation, the inlet of the rear fan can experience strong swirl distortion caused by the upward flow from the bottom to the top of the fuselage. Swirl distortion can be detrimental to the fan's operability and can cause aerodynamic and / or operational problems.

[0006] Accordingly, an improved inlet assembly for a rear fan that addresses the foregoing problems would be welcome in the art. More particularly, an inlet assembly for a rear fan that reduces swirl distortion would be particularly beneficial. Summary of the Invention

[0007] Aspects and advantages of the present invention will be set forth in part in the following description, or may be obvious from the description, or may be recognized by practicing the present invention.

[0008] In one aspect, the present disclosure is directed to a boundary layer ingestion fan assembly for mounting to the rear end of an aircraft fuselage. The boundary layer ingestion fan assembly includes a fan rotatable about a central axis of the boundary layer ingestion fan. Additionally, the fan includes a plurality of fan blades rotatable about a fan axis. The fan assembly further includes a nacelle surrounding the plurality of fan blades of the fan. The nacelle defines an inlet with respect to the aircraft fuselage. Thus, when the boundary layer ingestion fan is mounted at the rear end of the aircraft, the inlet extends generally around the aircraft fuselage. The fan assembly also includes a low-distortion inlet assembly mounted within the inlet for reducing swirl distortion of the airflow entering the inlet. More specifically, the inlet assembly includes a plurality of structural components circumferentially mounted at one or more predetermined locations within the inlet about the fan axis. The one or more predetermined locations generally have a swirl distortion exceeding a predetermined threshold. Thus, the placement of the structural components guides the airflow to reduce its swirl distortion. Additionally, the inlet assembly further includes at least one additional airflow conditioning element constructed within the inlet to further reduce the swirl distortion of the airflow entering the fan.

[0009] In another aspect, the present disclosure is directed to a low-distortion inlet assembly for reducing swirl distortion of the airflow entering a rear fan mounted to an aircraft fuselage. More specifically, the inlet assembly includes a plurality of structural components circumferentially mounted at one or more predetermined locations within the inlet about the fan axis. The one or more predetermined locations generally have a swirl distortion exceeding a predetermined threshold. Thus, the placement of the structural components guides the airflow to reduce its swirl distortion. Additionally, the inlet assembly further includes at least one additional airflow conditioning element constructed within the inlet to further reduce the swirl distortion of the airflow entering the fan.

[0010] In yet another aspect, the present disclosure is directed to a propulsion system for an aircraft having a fuselage. The propulsion system includes a rear engine configured to be mounted to the aircraft at its rear end. The rear engine defines a central axis and includes a fan having a plurality of fan blades rotatable about a fan axis along the central axis, and a nacelle surrounding the plurality of fan blades. The propulsion system also includes a low-distortion inlet assembly mounted within the inlet. The inlet assembly includes a plurality of structural components circumferentially mounted at one or more predetermined locations within the inlet in front of the fan about the fan axis of the fan, where the predetermined locations are defined by having a swirl distortion exceeding a predetermined threshold. Thus, the placement of the structural components guides the airflow to reduce its swirl distortion. Additionally, the inlet assembly further includes at least one additional airflow conditioning element constructed within the inlet to further reduce the swirl distortion of the airflow entering the fan.

[0011] Technical solution 1. A boundary layer ingestion fan assembly for installation at the rear end of an aircraft fuselage, the boundary layer ingestion fan assembly comprising:

[0012] A fan rotatable about a central axis of the boundary layer ingestion fan assembly, the fan including a plurality of fan blades rotatable about a fan shaft;

[0013] A nacelle surrounding the plurality of fan blades of the fan, the nacelle defining an inlet with respect to the aircraft fuselage, the inlet extending substantially around the aircraft fuselage when the boundary layer ingestion fan is installed at the rear end of the aircraft;

[0014] A low-distortion inlet assembly installed in the inlet, the inlet assembly comprising:

[0015] One or more structural components circumferentially installed around the fan shaft of the fan at a predetermined position within the inlet, the predetermined position including a swirl distortion exceeding a predetermined threshold; and

[0016] At least one air flow regulating element configured within the inlet to reduce the swirl distortion entering the fan.

[0017] Technical solution 2. The boundary layer ingestion fan assembly according to Technical solution 1, wherein the one or more structural components include at least one of inlet guide vanes or struts.

[0018] Technical solution 3. The boundary layer ingestion fan assembly according to Technical solution 2, wherein the boundary layer ingestion fan assembly further includes a plurality of inlet guide vanes grouped and placed at the predetermined position circumferentially around the fan shaft.

[0019] Technical solution 4. The boundary layer ingestion fan assembly according to Technical solution 3, wherein each of the plurality of inlet guide vanes includes a shape and orientation configured to reduce the swirl distortion entering the fan.

[0020] Technical solution 5. The boundary layer ingestion fan assembly according to Technical solution 3, wherein only a portion of the circumference of the fan shaft includes the plurality of structural components.

[0021] Technical solution 6. The boundary layer ingestion fan assembly according to any one of the foregoing technical solutions, wherein the at least one air flow regulating element includes at least one of a vortex generator, a contoured surface, a flap, or a variable inlet guide vane.

[0022] Technical solution 7. The boundary layer ingestion fan assembly according to Technical solution 6, wherein the at least one vortex generator or flap is installed on one of the plurality of structural components.

[0023] Aspect 8. The boundary layer ingestion fan assembly according to Aspect 6, wherein the profiled surface is located on the inner surface of the nacelle.

[0024] Aspect 9. The boundary layer ingestion fan assembly according to any one of the preceding aspects, wherein the boundary layer ingestion fan assembly further comprises at least one of trailing edge blowing, trailing edge suction, or angled flow injection configured to reduce flow distortion entering the fan.

[0025] Aspect 10. The boundary layer ingestion fan assembly according to any one of the preceding aspects, wherein the predetermined positions are spaced substantially evenly circumferentially relative to the fan axis.

[0026] Aspect 11. The boundary layer ingestion fan assembly according to Aspect 2, wherein the leading edge radius of one or more of the inlet guide vanes is designed to vary with the air flow conditions entering the fan.

[0027] Aspect 12. The boundary layer ingestion fan assembly according to Aspect 11, wherein the leading edge radius of one or more of the inlet guide vanes varies along the span direction with the air flow conditions entering the fan.

[0028] Aspect 13. A low-distortion inlet assembly for a rear fan configured to be mounted to an aircraft fuselage, the inlet assembly comprising:

[0029] a plurality of structural components mounted at one or more predetermined positions circumferentially around the fan axis within the inlet, the one or more predetermined positions including swirl distortion exceeding a predetermined threshold; and

[0030] at least one air flow regulating element configured within the inlet of the rear fan to reduce swirl distortion entering the fan.

[0031] Aspect 14. The inlet assembly according to Aspect 13, wherein the plurality of structural components comprises at least one of inlet guide vanes or struts.

[0032] Aspect 15. The inlet assembly according to Aspect 13 or Aspect 14, wherein the at least one air flow regulating element comprises at least one of a vortex generator, a profiled surface, a flap, or a variable inlet guide vane.

[0033] Aspect 16. The boundary layer ingestion fan assembly according to Aspect 10, wherein the leading edge radius of one or more of the inlet guide vanes varies along the span direction with the air flow conditions entering the fan.

[0034] Aspect 17. The inlet assembly according to Aspect 13, wherein the inlet assembly further includes a plurality of inlet guide vanes grouped and placed at the predetermined positions around the circumference of the fan shaft.

[0035] Aspect 18. The inlet assembly according to Aspect 13, wherein only a part of the circumference of the fan shaft includes the plurality of structural components.

[0036] Aspect 19. The inlet assembly according to Aspect 13, wherein the at least one air flow regulating element is mounted on one of the plurality of structural components.

[0037] Aspect 20. The inlet assembly according to Aspect 16, wherein the inlet assembly further includes trailing edge blowing, trailing edge suction, or angled flow injection configured to reduce the flow distortion entering the fan.

[0038] Aspect 21. A propulsion system for an aircraft having a fuselage, the propulsion system comprising:

[0039] A rear engine configured to be mounted to the aircraft at the rear end of the aircraft, the rear engine defining a central axis, the rear engine including a fan, the fan including a plurality of fan blades rotatable about a fan shaft, and a nacelle enclosing the plurality of fan blades, the nacelle defining an inlet with respect to the fuselage of the aircraft; and

[0040] A low-distortion inlet assembly mounted within the inlet, the inlet assembly including:

[0041] A plurality of structural components mounted around the circumference of the fan shaft of the fan within the inlet at one or more predetermined positions, the one or more predetermined positions including a swirl distortion exceeding a predetermined threshold; and

[0042] At least one air flow regulating element configured with respect to the inlet to reduce the swirl distortion entering the fan.

[0043] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and the appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] A complete and open disclosure of the invention, including the best mode thereof, for one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0045] Figure 1 A top view of an embodiment of an aircraft according to the present disclosure is shown;

[0046] Figure 2 shows Figure 1 a starboard view of an aircraft;

[0047] Figure 3 shows a schematic cross-sectional view of an embodiment of a gas turbine engine mounted on one of the wings of an aircraft mounted to Figure 1 ;

[0048] Figure 4 shows a schematic cross-sectional view of an embodiment of a rear engine according to the present disclosure;

[0049] Figure 5 shows a schematic cross-sectional view of a rear engine along the Figure 4 axial centerline of the rear engine to show an embodiment of an inlet assembly according to the present disclosure Figure 4 ;

[0050] Figure 6 shows a cross-sectional view of an embodiment of an inlet guide vane of an inlet guide vane assembly according to the present disclosure, particularly showing an inlet guide vane having a rotatable flap at its trailing edge;

[0051] Figure 7 shows a cross-sectional view of another embodiment of an inlet guide vane of an inlet guide vane assembly according to the present disclosure, particularly showing an inlet guide vane having a vortex generator constructed thereon;

[0052] Figure 8 shows a cross-sectional view of another embodiment of an inlet guide vane of an inlet guide vane assembly according to the present disclosure, particularly showing a straight inlet guide vane;

[0053] Figure 9 shows a cross-sectional view of yet another embodiment of an inlet guide vane of an inlet guide vane assembly according to the present disclosure, particularly showing an inverted inlet guide vane;

[0054] Figure 10 shows a cross-sectional view of still another embodiment of an inlet guide vane of an inlet guide vane assembly according to the present disclosure, particularly showing a symmetric inlet guide vane; and

[0055] Figure 11 shows a spanwise view of an embodiment of an inlet guide vane of an inlet guide vane assembly according to the present disclosure, particularly showing an inlet guide vane having a varying leading edge radius in the spanwise direction.

[0056] List of Components

[0057] 10 Aircraft

[0058] 12 Fuselage

[0059] 14 Longitudinal center line

[0060] 16 Nose section

[0061] 18 Tail section

[0062] 20 Wing

[0063] 22 Port side

[0064] 24 Starboard side

[0065] 26 Leading-edge flap

[0066] 28 Trailing-edge flap

[0067] 30 Vertical tail

[0068] 32 Rudder flap

[0069] 34 Horizontal tail

[0070] 36 Elevator flap

[0071] 38 Outer surface of fuselage

[0072] 40 Root

[0073] 100 Propulsion system

[0074] 102 Jet engine

[0075] 104 Jet engine

[0076] 106 BLI fan

[0077] 108 Generator

[0078] 110 Energy storage device

[0079] 200 Turbofan jet engine

[0080] 201 Longitudinal or axial center line

[0081] 202 Fan section

[0082] 204 Core turbine engine

[0083] 206 Casing

[0084] 208 Inlet

[0085] 210 Low-pressure compressor

[0086] 212 High-pressure compressor

[0087] 214 Combustion section

[0088] 216 High-pressure turbine

[0089] 218 Low-pressure turbine

[0090] 220 Jet exhaust section

[0091] 222 High-pressure shaft / rotating shaft

[0092] 224 Low-pressure shaft / rotating shaft

[0093] 226 Fan

[0094] 228 Blade

[0095] 230 Disk

[0096] 232 Actuating component

[0097] 234 Power gearbox

[0098] 236 Hub

[0099] 238 Fan casing / nacelle

[0100] 240 Exit guide vane

[0101] 242 Downstream section

[0102] 244 Bypass air flow path

[0103] 300 BLI fan

[0104] 302 Inlet assembly

[0105] 304 Fan

[0106] 306 Nacelle

[0107] 307 Structural component

[0108] 308 Inlet guide vane

[0109] 309 Strut

[0110] 310 Fan blade

[0111] 311 Inner surface

[0112] 312 Fan shaft

[0113] 314 Power source

[0114] 315 Air flow regulating element

[0115] 316 Gearbox

[0116] 318 Vortex generator

[0117] 318 Inlet guide vane group

[0118] 319 Profiled surface

[0119] 320 Upstream end

[0120] 321 Suction side

[0121] 322 Downstream end

[0122] 323 Pressure side

[0123] 324 Flap

[0124] 325 Body

[0125] 326 Radial axis

[0126] 328 First position

[0127] 330 Neutral position

[0128] 332 Second position

[0129] 334 Inlet

[0130] 336 Front end of the BLI fan

[0131] 338 Outlet guide vane

[0132] 340 Tail cone

[0133] 342 Nozzle

[0134] 344 Leading edge

[0135] 346 Trailing edge

[0136] 348 Mean camber line

[0137] 350 Chord line

[0138] 352 Leading edge radius

[0139] 354 Spanwise direction. Detailed implementation manners

[0140] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are shown in the accompanying drawings. The detailed description uses numerical and alphabetical labels to denote features in the drawings. Like or similar reference numerals in the drawings are used to denote like or similar parts of the present invention. As used herein, the terms "first", "second", and "third" may be used interchangeably to distinguish one component from another, and are not intended to denote the position or importance of the individual components. The terms "upstream" and "downstream" refer to the relative direction with respect to the fluid flow in the fluid passage. For example, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows.

[0141] Generally, the present disclosure is directed to a low-distortion inlet assembly for reducing the swirl distortion of the air flow entering a rear fan mounted to the fuselage of an aircraft. In addition, the inlet assembly includes a plurality of structural components (e.g., inlet guide vanes, struts, or the like) circumferentially mounted around the fan shaft of the fan at one or more predetermined positions, and at least one air flow regulating element configured within the inlet of the rear fan. More specifically, the predetermined positions have a swirl distortion exceeding a predetermined threshold. Accordingly, the inlet assembly is configured to reduce the swirl distortion entering the fan.

[0142] Since rows of inlet guide vanes are generally required for structural integrity in the rear fan, the inlet guide vanes can be customized to reduce the fan flow distortion by introducing variations in the guide vanes. For example, in one embodiment, the partial circumferential inlet guide vanes can be grouped at certain positions around the annulus with the highest distortion. In addition, one or more inlet guide vanes can be replaced with struts that provide structural support and flow turning to resist distortion. The inlet assembly of the present disclosure can also incorporate air flow regulating elements such as vortex generators, trailing edge blowing, trailing edge suction, and / or high-lift devices such as flaps attached to the structural components. In addition, the inlet assembly of the present disclosure can also include the definition or profiling of the internal area of the nacelle to induce a swirl-distortion-resistant flow field. Accordingly, the present invention reduces the swirl distortion entering the fan and reduces the weight and drag loss of the inlet guide vanes.

[0143] Now referring to the drawings, where like numerals represent like elements throughout the drawings, Figure 1 a top view of an embodiment of an aircraft 10 in accordance with the present disclosure is shown. Figure 2 As shown in Figure 1 a port side view of the aircraft 10 is shown. As shown jointly in Figure 1 and Figure 2 the aircraft 10 defines a longitudinal centerline 14, a vertical direction V, a lateral direction L, a front end 16, and a rear end 18 extending therethrough.

[0144] In addition, the aircraft 10 includes a fuselage 12 extending from a front end 16 of the aircraft 10 toward a rear end 18 of the aircraft 10, and a pair of wings 20. As used herein, the term "fuselage" generally includes all of the body of the aircraft 10, such as the tail of the aircraft 10 and the outer surface or skin 38 of the aircraft 10. The first of the wings 20 extends laterally outward from the port side 22 of the fuselage 12 relative to the longitudinal centerline 14, and the second of the wings 20 extends laterally outward from the starboard side 24 of the fuselage 12 relative to the longitudinal centerline 14. In addition, as shown in the illustrated embodiment, each of the wings 20 depicted includes one or more leading edge flaps 26 and one or more trailing edge flaps 28. The aircraft 10 may also include a vertical tail 30 having a rudder flap 32 for yaw control, and a pair of horizontal tails 34, each having an elevator flap 36 for pitch control. However, it should be recognized that in other exemplary embodiments of the present disclosure, the aircraft 10 may additionally or alternatively include any other suitable configuration of tails that may or may not extend directly along the vertical direction V or the horizontal / lateral direction L.

[0145] In addition, Figure 1 and Figure 2 the aircraft 10 includes a propulsion system 100 herein referred to as "system 100". The system 100 includes a pair of aircraft engines and a rear engine, with at least one of the aircraft engines mounted to each of the pair of wings 20. For example, as shown, the aircraft engines are configured as turbofan jet engines 102, 104 suspended below the wings 20 in a wing-under configuration. In addition, the rear engine is configured as an engine that ingests and consumes air forming the boundary layer on the fuselage 12 of the aircraft 10. Specifically, the rear engine is configured as a fan, i.e., a boundary layer ingestion (BLI) fan 106, which is configured to ingest and consume air forming the boundary layer on the fuselage 12 of the aircraft 10. In addition, as Figure 2 shown, the BLI fan 106 is mounted to the aircraft 10 at a location behind the wings 20 and / or the jet engines 102, 104 such that a center axis 15 extends therethrough. As used herein, the "center axis" refers to a midpoint line extending along the length of the BLI fan 106. In addition, for the illustrated embodiment, the BLI fan 106 is fixedly attached to the fuselage 12 at the rear end 18 such that the BLI fan 106 is incorporated into or fused with the tail section at the rear end 18. However, it should be recognized that in various other embodiments (some of which will be discussed below), the BLI fan 106 may alternatively be positioned at any suitable location at the rear end 18.

[0146] In various embodiments, the jet engines 102, 104 can be configured to provide power to the generator 108 and / or the energy storage device 110. For example, one or both of the jet engines 102, 104 can be configured to provide mechanical power from a rotating shaft (e.g., an LP shaft or an HP shaft) to the generator 108. Additionally, the generator 108 can be configured to convert the mechanical power into electrical power and provide this electrical power to one or more energy storage devices 110 and / or the BLI fan 106. Thus, in this embodiment, the propulsion system 100 can be referred to as a gas-electric propulsion system. However, it should be recognized that Figure 1 and Figure 2 the aircraft 10 and the propulsion system 100 depicted in are provided by way of example only, and in other exemplary embodiments of the present disclosure, any other suitable aircraft 10 can be provided with a propulsion system 100 configured in any other suitable manner.

[0147] Now referring to Figure 3 , in certain embodiments, the jet engines 102, 104 can be configured as high-bypass turbofan jet engines. More specifically, Figure 3 shows a schematic cross-sectional view of one embodiment of a high-bypass turbofan jet engine 200 herein referred to as "turbofan 200". In various embodiments, the turbofan 200 can represent the jet engines 102, 104. Additionally, as shown, the turbofan 200 engine 10 defines an axial direction A1 (extending parallel to the longitudinal centerline 201 provided for reference) and a radial direction R1. Generally, the turbofan 200 includes a fan section 202 and a core turbine engine 204 disposed downstream of the fan section 202.

[0148] In a particular embodiment, the core turbine engine 204 generally includes a generally tubular outer casing 206 defining an annular inlet 208. It should be recognized that approximate terms such as "substantially", "generally", "approximately", or "about" as used herein mean within a thirty percent margin of error. The outer casing 206 surrounds (in a series flow relationship): a compressor section including a booster or low-pressure (LP) compressor 210 and a high-pressure (HP) compressor 212; a combustion section 214; a turbine section including a high-pressure (HP) turbine 216 and a low-pressure (LP) turbine 218; and a jet exhaust nozzle section 220. A high-pressure (HP) shaft or rotor shaft 222 drivingly connects the HP turbine 216 to the HP compressor 212. A low-pressure (LP) shaft or rotor shaft 224 drivingly connects the LP turbine 218 to the LP compressor 210.

[0149] In addition, as shown, the fan section 202 includes a variable pitch fan 226 having a plurality of fan blades 228 coupled to a disk 230 in a spaced apart manner. As depicted, the fan blades 228 extend generally radially outward from the disk 230 along a radial direction R1. Each fan blade 228 is rotatable relative to the disk 230 about a pitch axis since the fan blades 228 are operatively coupled to a suitable actuation member 232 configured to collectively change the pitch of the fan blades 228. Accordingly, the fan blades 228, disk 230, and actuation member 232 may be rotated together about a longitudinal axis 12 by an LP shaft 224 spanning a power gearbox 234. In some embodiments, the power gearbox 234 includes a plurality of gears for stepping down the rotational speed of the LP shaft 224 to a more efficient rotational fan speed.

[0150] Still referring to Figure 3 , the disk 230 is covered by a rotatable front hub 236 aerodynamically contoured to facilitate air flow through the plurality of fan blades 228. Additionally, the fan section 202 includes an annular fan case or nacelle 238 that circumferentially encloses the fan 226 and / or at least a portion of the core turbine engine 204. It should be appreciated that the nacelle 238 may be configured to be supported relative to the core turbine engine 204 by a plurality of circumferentially spaced outlet guide vanes 240. Further, a downstream section 242 of the nacelle 238 may extend externally of the core turbine engine 204 to define a bypass air flow path 244 therebetween.

[0151] In addition, it should be appreciated that Figure 3 the turbofan engine 200 depicted in

[0152] is merely exemplary, and in other exemplary embodiments, the turbofan engine 20 may have any other suitable configuration. Additionally, it should be appreciated that in other exemplary embodiments, the jet engines 102, 104 may alternatively be configured as any other suitable aircraft engine. Figure 4 Now referring to Figure 1 and Figure 2 , a schematic cross-sectional side view of a rear engine according to various embodiments of the present disclosure is provided, such as a rear engine mounted to an aircraft 10 at a tail section 18 of the aircraft 10. More specifically, as shown, the rear engine is configured as a boundary layer ingestion (BLI) fan 300. The BLI fan 300 may be configured in substantially the same manner as the BLI fan 106 described above with reference to Figure 1 and Figure 2 , and the aircraft 10 may be configured in substantially the same manner as the exemplary aircraft 10 described above with reference to

[0153] More specifically, as shown, the BLI fan 300 defines an axial direction A2 extending along a central axis 15, which extends therethrough for reference. In addition, the BLI fan 300 defines a radial direction R2 and a circumferential direction C2 (not shown). Generally, the BLI fan 300 includes a fan 304 rotatable about the central axis 15, a nacelle 306 extending around at least a portion of the fan 304, and one or more structural members 307 extending between the nacelle 306 and the fuselage 12 of the aircraft 10. In addition, the fan 304 includes a plurality of fan blades 310 generally spaced apart in the circumferential direction C2. In addition, the structural member 307 extends between the nacelle 306 and the fuselage 12 of the aircraft 10 at a position in front of the plurality of fan blades 310. In addition, the nacelle 306 extends around and circumscribes the plurality of fan blades 310, and as Figure 4 shown, when the BLI fan 300 is mounted to the aircraft 10, it extends around the fuselage 12 of the aircraft 10 at the rear end 18 of the aircraft 10. It should be noted that as used herein, the term "nacelle" includes the nacelle and any structural fan casing.

[0154] Also as Figure 4 depicted, the fan 304 additionally includes a fan shaft 312 having a plurality of fan blades 310 attached thereto. Although not shown, the fan shaft 312 may be rotatably supported by one or more bearings located in front of the plurality of fan blades 310 and optionally one or more bearings located behind the plurality of fan blades 310. Such bearings may be any suitable combination of roller bearings, ball bearings, thrust bearings, etc.

[0155] In some embodiments, the plurality of fan blades 310 may be attached to the fan shaft 312 in a fixed manner, or alternatively, the plurality of fan blades 310 may be rotatably attached to the fan shaft 312. For example, the plurality of fan blades 310 may be attached to the fan shaft 312 such that the pitch of each of the plurality of fan blades 310 may be changed by a pitch changing mechanism (not shown), (e.g., all together). Changing the pitch of the plurality of fan blades 310 may increase the efficiency of the BLI fan 300 and / or may allow the BLI fan 300 to achieve a desired thrust profile. In the case of this exemplary embodiment, the BLI fan 300 may be referred to as a variable pitch BLI fan.

[0156] The fan shaft 312 is mechanically coupled to a power source 314 that is located in front of the plurality of fan blades 310 and at least partially within the fuselage 12 of the aircraft 10. Additionally, as shown, the fan shaft 312 is mechanically coupled to the power source 314 via a gearbox 316. The gearbox 316 may be configured to adjust the rotational speed of the power source 314 or, more precisely, the shaft 315 of the power source 314 such that the fan 304 of the BLI fan 300 rotates at a desired rotational speed. The gearbox 316 may be a fixed ratio gearbox or, alternatively, the gearbox 316 may define a variable gear ratio. For this embodiment, the gearbox 316 is operably connected to, for example, a controller of the aircraft 10 to change its ratio in response to one or more flight conditions.

[0157] In some embodiments, the BLI fan 300 may be configured to have a gas - electric propulsion system, such as the gas - electric propulsion system 100 described above with reference to Figure 1 the gas - electric propulsion system 100. In this embodiment, the power source 314 may be an electric motor that receives power from one or both of an energy storage device or a generator (such as Figure 1 and Figure 2 the energy storage device 110 or the generator 108 in ), where the generator 108 converts mechanical power received from one or more wing - mounted aircraft engines into electrical power. However, in other embodiments, the power source 314 may alternatively be any other suitable power source. For example, the power source 314 may alternatively be configured as a gas engine, such as a gas turbine engine or an internal combustion engine. Additionally, in some exemplary embodiments, the power source 314 may be located at any other suitable location, such as within the fuselage 12 of the aircraft 10 or within the BLI fan 300. For example, in some embodiments, the power source 314 may be configured as a gas turbine engine that is at least partially located within the BLI fan 300.

[0158] As briefly described above, the BLI fan 300 includes one or more structural components 307 for mounting the BLI fan 300 to the aircraft 10. More specifically, as Figure 5As shown, the structural member 307 can be configured as an inlet guide vane 308 for the fan 304 and / or as a strut 309. Additionally, it should be understood that the structural member 307 can be configured as a fixed inlet guide vane extending between the nacelle 306 and the fuselage 12 of the aircraft 10. Alternatively, the structural member 307 can be configured as a variable inlet guide vane. Further, as shown, the structural member 307 generally extends substantially along the radial direction R2 of the BLI fan 300 between the nacelle 306 and the fuselage 12 of the aircraft 10 for mounting the BLI fan 300 to the fuselage 12 of the aircraft 10. Thus, the structural member 307 can be shaped and / or oriented to direct and / or condition the airflow into the BLI fan 300, e.g., to increase the efficiency of the BLI fan 300 or to reduce the distortion of the air flowing into the BLI fan 300, which will be discussed in more detail below.

[0159] Still referring to Figure 4 , the BLI fan 300 also includes one or more outlet guide vanes 338 and a tail cone 340. The one or more outlet guide vanes 338 for the illustrated embodiment extend between the nacelle 306 and the tail cone 340 for directing the airflow through the BLI fan 300 and optionally for adding strength and stiffness to the BLI fan 300. The outlet guide vanes 338 can be evenly spaced along the circumferential direction C2 or can have any other suitable spacing. Additionally, the outlet guide vanes 338 can be fixed outlet guide vanes or, alternatively, variable outlet guide vanes. The inclusion of multiple outlet guide vanes 338 extending between the nacelle 306 and the tail cone 340 allows for maximizing the efficiency of the BLI fan 300.

[0160] Furthermore, behind the plurality of fan blades 310 and, for the illustrated embodiment, behind the one or more outlet guide vanes 338, the BLI fan 300 additionally defines a nozzle 342 between the nacelle 306 and the tail cone 340. Thus, the nozzle 342 can be configured to generate a certain amount of thrust from the air flowing therethrough. Additionally, the tail cone 340 can be shaped to minimize the amount of drag on the BLI fan 300. However, in other embodiments, the tail cone 340 can have any other shape and, for example, can be an end in front of the rear end of the nacelle 306 such that the tail cone 340 is enclosed by the nacelle 306 at the rear end. Additionally, in other embodiments, the BLI fan 300 can be configured not to generate any measurable amount of thrust and can instead be configured to ingest air from the boundary layer of the air of the fuselage 12 of the aircraft 10 and to add energy / accelerate this air to reduce the overall drag on the aircraft 10 (and thus increase the net thrust of the aircraft 10).

[0161] Specifically referring to Figure 4 and Figure 5, the BLI fan 300 defines an inlet 334 at the front end 336 between the nacelle 306 and the fuselage 12 of the aircraft 10. As described above, the nacelle 306 of the BLI fan 300 extends around the central axis 15 of the aircraft 10 and the fuselage 12 of the aircraft 10 at the rear end of the aircraft 10. Thus, as shown, when the BLI fan 300 is installed on the aircraft 10 (such as in the illustrated embodiment), the inlet 334 of the BLI fan 300 extends around the central axis 15 of the aircraft 10 and the fuselage 12 of the aircraft 10 by approximately three hundred and sixty degrees (360°). Additionally, in still other embodiments, the outer surface of the BLI fan 300 or rather the nacelle 306 may have any other suitable cross-sectional shape (as compared to the illustrated circular shape) along the axial direction A2, and the structural members 307 may not be evenly spaced along the circumferential direction C2.

[0162] Specifically referring to Figure 5 , a schematic cross-sectional view of an embodiment of the BLI fan 300 is shown looking along its axial centerline 15 to show the inlet assembly 302 according to the present disclosure. More specifically, as shown, the illustrated BLI fan 300 includes a plurality of structural members 307 circumferentially mounted at one or more predetermined positions around the fan shaft 312 of the BLI fan 300. For example, in certain embodiments, the predetermined positions as described herein have a swirl distortion exceeding a predetermined threshold. In other words, for certain embodiments, the air flow entering the BLI fan 300 can be evaluated to determine its swirl pattern. Thus, the position and / or number of the structural members 307 and the shape of the structural members 307 can be designed and selected to vary with the swirl pattern or distortion. In additional embodiments, as Figure 5 shown in, only a portion of the circumference of the fan shaft 312 may include the structural members 307. Alternatively, the structural members 307 may be spaced around the entire circumference of the fan shaft 312. Thus, in a particular embodiment, the structural members 307 may be evenly spaced along the circumferential direction C2 of the BLI fan 300 around the fan shaft 312. In an alternative embodiment, the inlet guide vane set 318 may be appropriately spaced along the circumferential direction C2 of the BLI fan 300 around the fan shaft 312 depending on the distortion pattern.

[0163] Furthermore, as shown in the illustrated embodiment, the structural members 307 may be circumferentially located relative to the circumference of the fan shaft 312 at approximately twelve o'clock, approximately three o'clock, approximately six o'clock, and / or approximately nine o'clock, respectively. It should be understood that the predetermined positions may be at the shown positions and any positions therebetween, and are intended to include positions having high swirl distortion and / or positions where the adjustment of the air flow will have the highest impact on correcting the swirl distortion. Additionally, as mentioned, the structural members 307 may include inlet guide vanes 308, struts 309, or the like, or any combination thereof.

[0164] Still referring toFigure 5 , the inlet assembly 302 may further include at least one air flow regulating element 315 constructed within the inlet 334. Thus, the inlet assembly 302 of the present disclosure is configured to reduce the swirl distortion of the air flow entering the fan 30. Accordingly, the present disclosure may include any suitable combination of the structural member 307 and / or the air flow regulating element 315 to counteract the swirl distortion of the air flow entering the BLI fan 300, examples of which are described in more detail below.

[0165] For example, as Figure 5 shown, the inlet assembly 302 may include a plurality of inlet guide vanes 308 (i.e., spaced along the circumferential direction C2 of the BLI fan 300) placed in groups 318 at predetermined positions around the circumference of the fan shaft 312, each generally extending in the radial direction R2 between the nacelle 306 and the fuselage 12 of the aircraft 10. For example, as shown in the figure, the inlet assembly 302 includes a single group 318 of three inlet guide vanes 308. In an alternative embodiment, the inlet assembly 30 may include more than one group 318 of inlet guide vanes 308 at any circumferential position having any suitable number of inlet guide vanes 308. Further, for embodiments having more than one inlet guide vane group 318, each group 318 may include the same number or a different number of inlet guide vanes 308. In a further embodiment, the inlet assembly 302 may include a plurality of inlet guide vanes 308 combined into a plurality of separate and distinct inlet guide vane groups 318 around the circumference of the fan shaft 312.

[0166] In addition, the inlet assembly 302 may include one or more struts 309 generally extending in the radial direction R2 between the nacelle 306 and the fuselage 12 of the aircraft 10. Generally, a strut is a structural member designed to resist longitudinal compression. Further, the struts 309 of the present disclosure are strategically placed at predetermined positions to more evenly redistribute the air flow entering the fan 300 circumferentially to reduce the swirl distortion at the inlet 334. For example, as shown in the figure, the illustrated inlet assembly 302 includes at least two struts 309, i.e., at three o'clock and six o'clock, respectively. In a further embodiment, the inlet assembly 302 may include more than two or less than two struts 309.

[0167] Specifically referring to Figures 5 - 7 , the air flow regulating element 315 may include at least one of a vortex generator 317 ( Figure 7 ), a contoured surface 319 ( Figure 5 ), a flap ( Figure 6 ) or any other air flow regulating element. More specifically, as Figure 5As shown, the inlet assembly 302 may include a defined area or a contoured surface 319 on the inner surface 311 of the nacelle 306, for example at the twelve o'clock position, which is configured to push the air flow radially inwards and away from the contoured surface 319. Thus, the profile of the inner surface 311 of the nacelle 306 is configured to cause a flow field that resists the swirling distortion of the air flow entering the inlet 334. In addition, the surface 311 of the nacelle 306 may also include one or more recesses configured to regulate the air flow.

[0168] In addition, as Figure 7 shown, one or more structural components 307 may include vortex generators 317 and / or flaps 334 constructed therewith. More specifically, Figure 5 and Figure 6 shows a cross-sectional view of an inlet guide vane 308 taken along the radial direction R2 that may be included in the inlet assembly 302. As shown, the inlet guide vane 308 extends between a front upstream end 320 and a rear downstream end 322. The front upstream end 320 includes a leading edge 344 of the inlet guide vane 308, and the rear downstream end 322 includes a trailing edge 346 of the inlet guide vane 308. The body 325 of the inlet guide vane 308 is fixed relative to the nacelle 306 of the BLI fan 300 and the fuselage 12 of the aircraft 10, and includes a pressure side 323 and a suction side 321. In addition, as shown, the inlet guide vane 308 may include one or more vortex generators 317 constructed on one or more of the pressure side 323 or the suction side 321. For example, as shown, the illustrated inlet guide vane 308 includes a single vortex generator 317 on its suction side 321. In additional embodiments, the inlet guide vane 308 and / or the strut 309 may include any number and / or type of vortex generators or similar surface features mounted to its surface to redirect the air flow entering the BLI fan 300.

[0169] In addition, as Figure 6 shown, the inlet guide vane 308 may also include an optional flap 324 at the rear end 320 configured to rotate about a generally radial axis 326. For example, as shown, the flap 324 is configured to rotate between a first position 328 (hatched), a neutral position 330, a second position 332 (hatched), and a potentially infinite number of positions therebetween. By rotating the flap 324 between the various positions, the inlet guide vane 308 can be configured to change the direction of the air flow flowing therethrough.

[0170] In yet another embodiment, the inlet assembly 302 may include trailing edge blowing or suction configured to reduce axial or swirl distortion of the air entering the BLI fan 300. Additionally, the inlet assembly 302 may include angled flow injection. Generally, trailing edge blowing involves flow injection in the direction of the air flow. In contrast, angled flow injection involves flow injection at an angle. Additionally, the flow injection may be steady or unsteady. Trailing edge blowing as used herein generally refers to the technique of injecting air into the inlet 334 at or near the trailing edge 346 of the inlet guide vane 308 or slightly upstream of the trailing edge 346. For example, in one embodiment, trailing edge blowing may include injecting an air stream into the main air stream through holes or slots configured within the airfoil. Trailing edge suction as used herein generally refers to the technique of discharging air from the inlet 334 at or near the trailing edge 346 of the inlet guide vane 308 or slightly upstream of the trailing edge 346. Thus, both trailing edge blowing and trailing edge suction are configured to condition the air flow entering the inlet 334 in order to reduce air flow distortion entering the fan 300. Additionally, trailing edge blowing may be achieved through steady or pulsating blowing aligned with or angled to the air flow to achieve the same effect as a micro-vortex generator or a splitter wing.

[0171] Now referring Figures 8 - 10 , a cross-sectional view of an additional embodiment of the inlet guide vane 308 of the present disclosure is shown. It should be understood that such features may also apply to the struts. As shown, each inlet guide vane 308 may have a unique shape and / or orientation at a particular location in the fan 300 corresponding to the air flow conditions of the air entering the BLI fan 300. Thus, any combination of shapes may be used in the inlet assembly 302 and may be selected based on the determined swirl distortion of the air flow entering the BLI fan 300.

[0172] For example, as shown, each inlet guide vane 308 may have a curved upright airfoil section ( Figure 8 ), a curved inverted airfoil section ( Figure 9 ), or a symmetric airfoil section ( Figure 10 ). More specifically, as Figure 8 shown, the curved upright inlet guide vane 308 generally has a mean camber line 348 above the chord line 350 of the airfoil, where the trailing edge 346 has a downward direction. This curved airfoil typically generates lift at zero angle of attack and as the air moves along the trailing edge 346, the air is deflected downward. As Figure 9 shown, the inverted inlet guide vane 308 generally has a mean camber line 348 below the chord line 350 of the airfoil, where the trailing edge 346 has an upward direction. When the upper side of the curved airfoil is downward, the angle of attack may be adjusted so that the lift is upward. In contrast, as Figure 10 shown, the mean camber line 348 and the chord line 350 of the symmetric airfoil are the same (i.e., lines 348, 350 overlap and there is no cavity).

[0173] It should be understood that the lift depends on the shape of the airfoil, in particular the amount of curvature (i.e., the curvature such that the upper surface is more convex than the lower surface). In other words, increasing the curvature of the airfoil causes a greater deflection of the flow, which in turn generally increases the lift. The local deflection of the flow can be used to counteract local flow distortions and results in a more uniform flow profile being ingested by the fan.

[0174] In addition, generally as Figures 6 - 11 shown, the leading edge radius 352 of one or more of the inlet guide vanes 308 can be designed to reduce the swirl distortion of the air flow entering the BLI fan 300. In addition, as Figure 10 shown, in some embodiments, the leading edge radius 352 of one or more inlet guide vanes 308 can vary (e.g., become larger or smaller) along the spanwise direction 354 with the air flow conditions entering the BLI fan 300. Thus, the leading edge radius 352 of each inlet guide vane 308 can be designed according to the flow conditions it receives. In addition, as shown, the bend angle (i.e., the curvature) of the individual guide vanes 308 can also vary along the spanwise direction 354 to effectively make the flow more uniform at the discharge of the inlet guide vanes 308.

[0175] This written description uses examples to disclose the invention, including the best mode, and also enables those skilled in the art to practice the invention, including making and using any device or system and performing any included method. The scope of the invention that can be patented is defined by the claims and may include other examples that occur to those skilled in the art. If these other examples have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not differ substantially from the literal language of the claims, then these other examples are intended to be within the scope of the claims.

Claims

1. A propulsion system (100) for an aircraft (10) having a fuselage (12), the propulsion system (100) comprising: Engines (102, 104, 106) configured to be mounted to the aircraft (10), the engines (102, 104, 106) defining a central axis (15), the engines (102, 104, 106) comprising: a fan (226, 304) including a plurality of fan blades (228, 310) rotatable about a fan axis (230, 312); and a nacelle (238, 306) surrounding the plurality of fan blades (228, 310), the nacelle (238, 306) and the fuselage (12) of the aircraft (10) together defining an inlet (334); and a low distortion inlet assembly (302) mounted within the inlet (334), the inlet assembly (302) comprising: a plurality of structural members (307) circumferentially mounted at one or more predetermined locations about the fan axis (230, 312) of the fan (226, 304) within the inlet (334), the one or more predetermined locations including a swirl distortion exceeding a predetermined threshold; and at least one airflow regulating element (315) configured with the inlet (334) to reduce swirl distortion entering the fan (226, 304).

2. The propulsion system (100) according to claim 1, characterized in that, The one or more structural members (307) include at least one of inlet guide vanes or struts.

3. The propulsion system (100) according to claim 2, characterized in that, The propulsion system (100) further includes a plurality of inlet guide vanes (308) grouped (318) and placed at the predetermined locations about the circumference of the fan axis (230, 312).

4. The propulsion system (100) according to claim 3, characterized in that, Each of the plurality of inlet guide vanes (308) includes a shape and orientation configured to reduce swirl distortion entering the fan (226, 304).

5. The propulsion system (100) according to claim 3, characterized in that, Only a portion of the circumference of the fan axis (230, 312) includes the plurality of structural members (307).

6. The propulsion system (100) according to any one of the preceding claims, characterized in that, The at least one airflow regulating element (315) includes at least one of a vortex generator (317), a contoured surface (319), a flap (324), or a variable inlet guide vane (308).

7. The propulsion system (100) according to claim 6, characterized in that, The at least one vortex generator or flap (324) is mounted on one of the plurality of structural members (307).

8. The propulsion system (100) according to claim 6, characterized in that, The contoured surface (319) is located on an inner surface of the nacelle (238, 306).

9. The propulsion system (100) according to any one of claims 1 - 5, characterized in that, The propulsion system (100) further includes at least one of trailing edge blowing, trailing edge suction, or angled flow injection configured to reduce flow distortion entering the fan (226, 304).

10. The propulsion system (100) according to any one of claims 1 - 5, characterized in that, The predetermined locations are spaced apart substantially evenly about the circumference of the fan axis (230, 312).

11. The propulsion system (100) according to claim 2, characterized in that, The leading edge radius (352) of one or more of the inlet guide vanes (308) is designed to vary with the airflow conditions entering the fan (226, 304).

12. The propulsion system (100) according to claim 11, characterized in that, The leading edge radius (352) of one or more of the inlet guide vanes (308) varies along the spanwise direction (354) with the airflow conditions entering the fan (226, 304).

13. A low distortion inlet assembly (302) for a fan (226, 304) to be mounted to the fuselage (12) of an aircraft (10), the inlet assembly (302) comprising: A plurality of structural components (307) mounted at one or more predetermined positions around the circumference of the fan shafts (230, 312) of the fans (226, 304) within the inlet (334), the one or more predetermined positions including swirl distortion exceeding a predetermined threshold; And At least one air flow regulating element (315) configured within the inlet (334) of the fan (226, 304) to reduce swirl distortion entering the fan (226, 304).

14. The inlet assembly (302) according to claim 13, characterized in that, The plurality of structural components (307) includes at least one of inlet guide vanes (308) or struts (309).

15. The inlet assembly (302) according to claim 13 or claim 14, characterized in that, The at least one air flow regulating element (315) includes at least one of a vortex generator (317), a contoured surface (319), a flap (324), or variable inlet guide vanes (308).

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