Turbofan engine and method of reducing air flow separation therein

A turbofan engine is provided. The turbofan engine includes a nacelle housing including a radially outer wall and a radially inner wall that defines an interior cavity within the nacelle housing. The turbofan engine also includes a fan assembly positioned at least partially within the interior cavity. A flow passage is defined between the radially outer wall and the radially inner wall for channeling a flow of air therethrough. The flow passage is configured to couple a portion of the interior cavity upstream from the fan assembly in flow communication with an ambient environment exterior from the radially outer wall.

BACKGROUND

The present disclosure relates generally to turbofan engines and, more specifically, to systems and methods of reducing air flow separation in a turbofan engine with a bias-flow acoustic liner.

At least some known gas turbine engines, such as turbofans, include a fan, a core engine, and a power turbine. The core engine includes at least one compressor, a combustor, and a high-pressure turbine coupled together in a serial flow relationship. More specifically, the compressor and high-pressure turbine are coupled through a shaft to form a high-pressure rotor assembly. Intake air is channeled through the fan, and air entering the core engine is mixed with fuel and ignited to form a high energy gas stream. The high energy gas stream flows through the high-pressure turbine to rotatably drive the high-pressure turbine such that the shaft rotatably drives the compressor. After being discharged from the high-pressure turbine, the gas stream continues to expand as it flows through a low-pressure turbine positioned aft of the high-pressure turbine. The low-pressure turbine includes a rotor assembly coupled to a drive shaft and a fan. The low-pressure turbine rotatably drives the fan through the drive shaft.

Many modern commercial aircraft operate in high velocity crosswind conditions and low-speed operation at takeoff and landing, for example. The combination of such operating conditions can cause distortions in the intake air channeled towards the fan, which can cause flow separation at an interior surface of an engine nacelle housing. Flow separation at the interior surface of an engine nacelle housing facilitates forming rotating vortices within the engine nacelle housing, which can cause a rotating stall condition within the turbofan. At least some known engine nacelle housings are designed to mitigate flow separation within the turbofan. For example, at least some known engine nacelle housings are relatively thick and have a forward portion that extends past a forward face of the fan to restrict high velocity crosswind from distorting the flow of the intake air before entering the fan. However, further design modifications may be necessary to reduce distortions to the flow of the intake air.

BRIEF DESCRIPTION

In one aspect, a turbofan engine is provided. The turbofan engine includes a nacelle housing including a radially outer wall and a radially inner wall that defines an interior cavity within the nacelle housing. The turbofan engine also includes a fan assembly positioned at least partially within the interior cavity. A flow passage is defined between the radially outer wall and the radially inner wall for channeling a flow of air therethrough. The flow passage is configured to couple a portion of the interior cavity upstream from the fan assembly in flow communication with an ambient environment exterior from the radially outer wall.

In another aspect, an aircraft is provided. The aircraft includes a fuselage, a wing structure coupled to the fuselage, and a turbofan engine coupled to at least one of the fuselage and the wing structure. The turbofan engine includes a nacelle housing including a radially outer wall and a radially inner wall that defines an interior cavity within the nacelle housing. The turbofan engine also includes a fan assembly positioned at least partially within the interior cavity. A flow passage is defined between the radially outer wall and the radially inner wall for channeling a flow of air therethrough. The flow passage is configured to couple a portion of the interior cavity upstream from the fan assembly in flow communication with an ambient environment exterior from the radially outer wall.

In yet another aspect, a method of reducing air flow separation in a turbofan engine is provided. The method includes defining a flow passage between a radially outer wall and a radially inner wall of a nacelle housing of the turbofan engine. The flow passage is configured to couple a portion of an interior cavity of the nacelle housing upstream from a fan assembly in flow communication with an ambient environment exterior from the radially outer wall. The method further includes channeling a flow of air between the interior cavity and the ambient environment.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to systems and methods of reducing air flow separation in a turbofan engine. More specifically, the systems described herein include a flow passage defined in a nacelle housing upstream from a fan assembly of a turbofan engine. The flow passage is for channeling a flow of air between an interior cavity of the nacelle housing and an ambient environment exterior of the nacelle housing. In one embodiment, an actuating door in the nacelle housing is selectively operable between an open position and a closed position to allow the flow of air to be channeled therethrough. An acoustic liner is positioned within the nacelle housing, which acts as an acoustic bias-flow liner when the actuating door is open, and acts as a conventional liner when the door is closed. The flow of air is either combined with a flow of intake air channeled towards the fan assembly, or is drawn from an interior cavity of the nacelle housing to facilitate re-attaching the intake air to an inner surface of the nacelle housing to reduce distortions in the intake air caused by high crosswinds blowing transversely relative to a centerline of the turbofan engine. As such, when channeled through the acoustic bias-flow liner, improvements in flow separation and noise reduction are achieved.

FIG. 1is a schematic illustration of an aircraft10. Aircraft10includes a wing structure12coupled to and extending from a fuselage14. Aircraft10also includes turbofan engines16coupled to wing structure12. Alternatively, turbofan engines16are coupled to at least one of fuselage14and wing structure12. The plurality of structures shown on aircraft10is for illustrative purposes only, and it should be understood that aircraft10additionally includes a large number of other structures. As used herein, the term “aircraft” may include, but is not limited to only including, airplanes, unmanned aerial vehicles (UAVs), gliders, helicopters, and/or any other object that travels through airspace. Moreover, it should be understood that, although an aerospace example is shown, the principles of the disclosure may be applied to other structures, such as a maritime structure or an automotive structure.

FIG. 2is a schematic illustration of an exemplary turbofan engine16. Turbofan engine16includes a booster compressor18, a high-pressure compressor20, and a combustor assembly22. Turbofan engine16also includes a high-pressure turbine24and a low-pressure turbine26arranged in a serial, axial flow relationship. Booster compressor18and low-pressure turbine26are coupled along a first shaft28, and high-pressure compressor20and high-pressure turbine24are coupled along a second shaft30.

In operation, air flows through booster compressor18and compressed air is supplied from booster compressor18to high-pressure compressor20. The compressed air is discharged towards combustor assembly22and mixed with fuel to form a flow of combustion gas discharged towards turbines24and26. The flow of combustion gas drives turbines24and26about a centerline32of turbofan engine16.

FIG. 3is an enlarged schematic illustration of a portion of turbofan engine16in a first operational position, andFIG. 4is an enlarged schematic illustration of the portion of turbofan engine16in a second operational position. In the exemplary embodiment, turbofan engine16includes a nacelle housing100having a radially outer wall102and a radially inner wall104that defines an interior cavity106within nacelle housing100. A fan assembly108is positioned within nacelle housing100upstream from booster compressor18(shown inFIG. 2). A flow passage110is defined between radially outer wall102and radially inner wall104for channeling a flow of air112therethrough. More specifically, flow passage110couples a portion of interior cavity106upstream from fan assembly108in flow communication with an ambient environment114exterior from radially outer wall102. For example, in one embodiment, radially outer wall102is defined on a high pressure side of nacelle housing100, and radially inner wall104is defined on a low pressure side of nacelle housing100. As such, the flow of air112naturally flows from exterior of nacelle housing100towards interior cavity106via flow passage110.

In the exemplary embodiment, nacelle housing100includes an actuating door116coupled to radially outer wall102. Actuating door116is selectively operable between a closed position and an open position at least partially based on the velocity of aircraft10(shown inFIG. 1), and a velocity of a crosswind118at radially outer wall102. For example, referring toFIG. 4, when the velocity of crosswind118is greater than a predetermined threshold, or if aircraft10is traveling at a relatively low-speed first velocity (e.g., at takeoff or landing), actuating door116is in an open position120to facilitate channeling the flow of air112therethrough. More specifically, when in open position120, the space once occupied by actuating door116defines an opening122in radially outer wall102, which at least partially defines flow passage110. In the exemplary embodiment, crosswind118is generally misaligned with centerline32of turbofan engine16, which facilitates distorting a flow of intake air124channeled towards fan assembly108.

Alternatively, referring toFIG. 3, when the velocity of crosswind118is less than the predetermined threshold, or if aircraft10is traveling at a greater second velocity (e.g., at cruise), actuating door116is in a closed position126to increase the aerodynamic efficiency of nacelle housing100. While shown as a sliding door that retracts within nacelle housing100, it should be understood that actuating door116may have any range of motion to enable it to be selectively operable between open position120and closed position126. Moreover, as will be described in more detail below, while shown as being channeled externally from nacelle housing100towards interior cavity, it should be understood that the flow of air112can be drawn from interior cavity106to reduce flow separation therein.

FIG. 5is a cross-sectional illustration of a portion of flow passage110that may be used with turbofan engine16, in accordance with a first embodiment of the disclosure. In the exemplary embodiment, nacelle housing100(shown inFIGS. 3 and 4) further includes an acoustic liner128positioned between radially outer wall102(shown inFIGS. 3 and 4) and radially inner wall104. More specifically, acoustic liner128includes a honeycomb structure130coupled to radially inner wall104, and a face sheet132coupled to honeycomb structure130on an opposing side thereof from radially inner wall104.

At least one of radially inner wall104and acoustic liner128have one or more openings or channels defined therein that at least partially define flow passage110. More specifically, nacelle housing100includes a plurality of first openings134defined in radially inner wall104for channeling the flow of air112therethrough. The plurality of first openings134are positioned upstream from fan assembly108. Moreover, honeycomb structure130includes a plurality of channels136defined therein, and face sheet132includes a plurality of second openings138defined therein and a sheet (not shown) of wire mesh having openings defined therein, for at least partially defining flow passage110. As such, opening122in radially outer wall102(each shown inFIG. 4), second openings138, respective channels136in honeycomb structure130, and first openings134are coupled in a serial flow relationship to enable the flow of air112to reduce flow separation of the flow of intake air124at an inner surface140of radially inner wall104.

FIG. 6is a cross-sectional illustration of the portion of flow passage110that may be used with turbofan engine16, in accordance with a second embodiment of the disclosure. In the exemplary embodiment, the plurality of first openings134are angled obliquely relative to inner surface140of radially inner wall104such that the flow of air112that naturally flows from exterior of nacelle housing100is directed towards fan assembly108. More specifically, first openings134are angled such that an inlet142of each first opening134is positioned radially outward from an outlet144of each first opening134. As such, the flow of air112is combined with the flow of intake air124to reduce flow separation at inner surface140in a more efficient manner.

FIG. 7is a cross-sectional illustration of the portion of flow passage110that may be used with turbofan engine16, in accordance with a third embodiment of the disclosure. In the exemplary embodiment, nacelle housing100includes an actuating device146that draws a flow of air148from interior cavity106towards exterior of nacelle housing100via flow passage110. More specifically, the flow of air148is drawn through first openings134, channels136in honeycomb structure130, second openings138, and opening122in radially outer wall102(each shown inFIG. 4) for discharge towards ambient environment114(shown inFIGS. 3 and 4). Drawing the flow of air148from interior cavity106facilitates re-attaching the flow of intake air124to inner surface140of radially inner wall104.

In one embodiment, the plurality of first openings134are angled obliquely relative to inner surface140of radially inner wall104such that the flow of air drawn from interior cavity106flows through the plurality of first openings134in a downstream direction. More specifically first openings134are angled such that each inlet142is positioned radially inward from each outlet144of first openings134. As such, the flow of intake air124is re-attached to inner surface140of radially inner wall104in a more efficient manner.

The systems and methods described herein relate to improving the performance of turbofan engines operating in high crosswind conditions. More specifically, the systems and methods are for reducing air flow separation of intake air in the nacelle housing of a turbofan engine caused by crosswind distortions. The system provides a flow passage in the nacelle housing upstream from a fan assembly of the turbofan engine. The flow passage facilitates channeling a flow of air between an interior cavity of the nacelle housing and an ambient environment exterior of the nacelle housing. As such, the flow of air facilitates reducing flow separation within the nacelle housing.

An exemplary technical effect of the system and methods described herein includes at least one of: (a) reducing flow separation of intake air at an inner surface of a nacelle housing; (b) reducing the likelihood of rotating vortices from forming within a turbofan engine; (c) improving the thrust and efficiency of a turbofan engine when operating in high crosswind conditions; and (d) using an acoustic bias-flow liner to reduce noise from the engines at takeoff in high crosswind conditions.

Exemplary embodiments of a turbofan engine and related components are described above in detail. The system is not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the configuration of components described herein may also be used in combination with other processes, and is not limited to practice with only turbofan engines and related methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many applications where reducing flow separation in a housing is desirable.