Variable area exhaust mixer for a gas turbine engine

A variable area exhaust mixer is provided for a gas turbine engine. The variable area exhaust mixer includes an outer wall with a multiple of doors. Each of the multiple of doors is operable to control a passage entrance into at least one of a multiple of circumferentially arrayed vanes with a respective strut flow passage which essentially alters its bypass ratio during flight to match requirements.

BACKGROUND

The present disclosure relates to variable cycle gas turbine engines, and more particularly to an exhaust mixer therefor.

Variable cycle gas turbine engines power aircraft over a range of operating conditions, yet achieve countervailing objectives such as high specific thrust and low fuel consumption. The variable cycle gas turbine engine essentially alters its bypass ratio during flight to match requirements. This facilitates efficient performance over a broad range of altitudes and flight conditions to selectively generate high thrust for conditions requiring maximum propulsion, e.g., takeoff or maneuvers, and optimized fuel efficiency for cruise and loiter operation.

An exhaust nozzle controls the thermodynamic cycle of the gas turbine engine and enhances the thrust produced by the gas turbine engine flow stream. In variable cycle gas turbine engines, the size of the exhaust nozzle may need to vary considerably to accommodate large changes in the cycle and the individual flow streams may require a variable nozzle to maximize performance and efficiency.

SUMMARY

A variable area exhaust mixer for a gas turbine engine, according to one disclosed non-limiting embodiment of the present disclosure, includes an outer wall with a multiple of doors. Each of the multiple of doors is operable to control a passage entrance to a strut flow passage within at least one of a multiple of circumferentially arrayed vanes.

In a further embodiment of the present disclosure, each of the multiple of doors hinge inward toward the multiple of circumferentially arrayed vanes.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the multiple of doors hinge inward toward each respective circumferentially arrayed vane of the multiple of circumferentially arrayed vanes.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the multiple of doors hinge about an axis generally parallel to a longitudinal engine axis of a gas turbine engine.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the multiple of circumferentially arrayed vanes includes at least one trailing edge flap operable to control a passage exhaust from the respective strut flow passage.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the trailing edge flaps hinge about an axis generally transverse to a longitudinal engine axis of the gas turbine engine.

In a further embodiment of any of the foregoing embodiments of the present disclosure, at least one of the multiple of circumferentially arrayed vanes includes one or more spraybars from a fuel manifold to selectively direct fuel through the multiple of circumferentially arrayed vanes to provide thrust augmentation.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the multiple of circumferentially arrayed vanes includes a respective trailing edge flap operable to control a passage exhaust from the respective strut flow passage. Each of the trailing edge flaps hinge about an axis generally transverse to a longitudinal engine axis of the gas turbine engine. Each of the multiple of doors hinge about an axis generally parallel to the longitudinal engine axis of a gas turbine engine.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the multiple of doors hinge inward toward each respective circumferentially arrayed vane of the multiple of circumferentially arrayed vanes.

A variable cycle gas turbine engine, according to another disclosed non-limiting embodiment of the present disclosure, includes a variable area exhaust mixer between a third stream fan flow path and a core flow path. The variable area exhaust mixer is operable to control flow from the third stream fan flow path to the core flow path through a multiple of circumferentially arrayed vanes.

In a further embodiment of any of the foregoing embodiments of the present disclosure, a second stream fan flow path is included radially inboard of the third stream fan flow path and radially outboard of the core flow path.

In a further embodiment of any of the foregoing embodiments of the present disclosure, the second stream fan flow path and the third stream fan flow path is downstream of a fan section.

In a further embodiment of any of the foregoing embodiments of the present disclosure, the variable area exhaust mixer includes a multiple of doors. Each of the multiple of doors is operable to control a passage entrance into at least one of the multiple of circumferentially arrayed vanes with a respective strut flow passage.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the multiple of doors hinge about an axis generally parallel to a longitudinal engine axis of a gas turbine engine.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the multiple of circumferentially arrayed vanes includes a respective trailing edge flap operable to control a passage exhaust from the respective strut flow passage.

In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the trailing edge flaps hinge about an axis generally transverse to a longitudinal engine axis of the gas turbine engine.

In a further embodiment of any of the foregoing embodiments of the present disclosure, at least one of the multiple of circumferentially arrayed vanes includes one or more spraybars from a fuel manifold to direct fuel through the multiple of circumferentially arrayed vanes to selectively inject fuel to provide thrust augmentation.

In a further embodiment of any of the foregoing embodiments of the present disclosure, a tail cone is included radially inboard of the multiple of circumferentially arrayed vanes.

A method of operating a gas turbine engine, according to another disclosed non-limiting embodiment of the present disclosure, includes selectively changing an area-ratio between a fan flow in a third stream bypass flow path and a core flow through a core flow path downstream of a turbine section.

In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes selectively changing the area-ratio by about 20%-50%.

DETAILED DESCRIPTION

FIGS. 1A and 1Bschematically illustrate example architectures for a gas turbine engine10. The gas turbine engine10is disclosed herein as a fixed cycle (two-stream architecture;FIG. 1A) or a variable cycle (three-stream architecture;FIG. 1B). Each gas turbine engine10is a multi-spool turbofan that generally includes a fan section12, a high pressure compressor section14, a combustor section18, a high pressure turbine section20, a low pressure turbine section22, a turbine exhaust case section24, an augmentor section26, an exhaust duct section28and a nozzle section30along a central longitudinal engine axis A. Although depicted with specific architectures in the disclosed non-limiting embodiments, it should be understood that the concepts described herein are not limited to only the illustrated architectures.

A low spool34and a high spool36rotate about the engine central longitudinal axis A relative to an engine case structure48. The low pressure turbine section22of the low spool34drives the fan section12directly or through a geared architecture32to drive the first stage of fan section12at a lower speed than subsequent stages. Example geared architectures32include an epicyclic transmission, namely a planetary or star gear system, that may be located in various engine sections such as forward of the high pressure compressor section14or aft of the low pressure turbine section22.

The engine case structure48generally includes an outer case structure50, an intermediate case structure52and an inner case structure54(all illustrated somewhat schematically). Various static structures individual or collectively form the case structure48to essentially define an exoskeleton that supports rotation of the spools34,38.

In the fixed cycle (two-stream architecture;FIG. 1A), the fan section12communicates airflow into a second stream bypass flow path58and a core flow path60. In the variable cycle (three-stream architecture;FIG. 1B), the fan section12communicates bypass flow into a third stream bypass flow path56as well as the second stream bypass flow path58and the core flow path60. The third stream bypass flow path56is generally annular in cross-section and defined by the outer case structure50and an additional intermediate case structure53(seeFIG. 1B). The second stream bypass flow path58is also generally annular in cross-section and defined by the intermediate case structure52and the inner case structure54. The core flow path60is generally annular in cross-section and defined by the inner case structure54. The second stream bypass flow path58is defined radially inward of the third stream bypass flow path56and the core flow path60is radially inward of the second stream bypass flow path58. Various crossover and cross-communication flow paths may alternatively or additionally be provided to provide control of the flow streams, bypass ratio, and thus engine cycle.

The second stream bypass flow path58may include a flow control mechanism62(illustrated schematically) of various configurations such as electrical, pneumatic or mechanically operated blocker doors that operate as a throttle point. The flow control mechanism62, either alone or in combination with other control mechanisms, is selectively operable to control airflow through the second stream bypass flow path58.

The core flow is further compressed by the high pressure compressor section14, mixed and burned with fuel in the combustor section18, then expanded through the high pressure turbine section20and the low pressure turbine section22. The turbines sections20,22rotationally drive the respective spools34,38in response to the expansion. It should be further appreciated that other architectures such as a three-spool architecture will also benefit herefrom.

Downstream of the turbine sections20,22the exhaust duct section28may be circular in cross-section as typical of an axisymmetric augmented low bypass turbofan or may include non-axisymmetric cross-section segments. In addition to the various cross-sections, the exhaust duct section28may be non-linear with respect to the central longitudinal engine axis A to form, for example, a serpentine shape to block direct view to the turbine sections. In addition to the various cross-sections and the various longitudinal shapes, the exhaust duct section28may terminate in the nozzle section30such as a convergent-divergent, non-axisymmetric, two-dimensional (2D) vectorable, or other nozzle arrangement architectures.

In the fixed cycle (two-stream architecture;FIG. 1A), the exhaust nozzle section30(illustrated schematically) receives a mixed flow66from the second stream bypass flow path58and the core flow path60combined by the exhaust mixer70. In the variable cycle (three-stream architecture; seeFIG. 1B), the nozzle section30may also include a radially outboard third stream exhaust nozzle64(illustrated schematically). The third stream exhaust nozzle64may be of various nozzle architectures.

The variable area exhaust mixer70(also shown inFIG. 2) may be located upstream or adjacent a convergent region68within the exhaust duct section28. That is, the variable area exhaust mixer70is axially located at an exhaust mixing plane where the second stream bypass flow path58joins the core flow path60to modulate bypass and core flow stream mixing. As the second stream bypass flow path58is generally at only a relatively slightly higher pressure than the flow stream from the core flow path60, the variable area exhaust mixer70facilitates injection of the fan flow stream into the relatively high pressure core flow stream. The relatively high velocity of the core flow stream through the exhaust mixer70facilitates this injection by lowering the static pressure in the core stream60as it passes through the exhaust mixer70.

In the variable cycle (three-stream architecture; seeFIG. 1B), the variable area exhaust mixer70is axially located at the exhaust mixing plane to mix the fan flow stream from the third stream bypass flow path56with the core flow stream of the core flow path60. As the third stream bypass flow path56is generally at only a relatively slightly higher pressure or even lower pressure than the flow stream from the core flow path60, the variable area exhaust mixer70facilitates injection of the fan flow stream into the relatively high pressure core flow stream. The relatively high velocity of the core flow stream through the exhaust mixer70facilitates this injection by lowering the static pressure in the core stream60as it passes through the exhaust mixer70.

With reference toFIG. 2, the variable area exhaust mixer70includes a multiple of circumferentially arrayed and radially extending vanes72. The multiple of circumferentially arrayed vanes72may extend between the inner case structure54and the intermediate case structure52. In one disclosed non-limiting embodiment, the intermediate case structure52terminates with an outer wall76of the variable area exhaust mixer70and the inner case structure54terminates with a tail cone74.

The outer wall76of the variable area exhaust mixer70includes a multiple of doors78each of which controls a passage entrance80to a plenum81that is open to a strut flow passage82formed through each of the respective vanes72. In one disclosed non-limiting embodiment, each of the multiple of doors78hinges inward into the plenum81about a respective axis D generally parallel to the central longitudinal engine axis A. It should be appreciated that door arrangements such as sliding doors may alternatively or additionally be utilized. In this disclosed non-limiting embodiment, each two (2) of the multiple of doors78are located radially outbound of each strut flow passage82to provide an inwardly directed rectilinear ramped passage entrance80to provide a relatively large flow area for the fan flow stream(s). The multiple of doors78thereby provide significant flow capacity that selectively increases the bypass area-ratio between the fan flow stream and the core flow stream when the variable area exhaust mixer70is open.

With reference toFIG. 3, each of the multiple of circumferentially arrayed vanes72include first and second walls84,86, joined at a leading edge88and a trailing edge90to define the strut flow passage82. The first and second walls84,86may form an airfoil or other aerodynamic shape.

At least one of the first and second walls84,86of each of the multiple of circumferentially arrayed vanes72includes a trailing edge flap92. When the trailing edge flap is closed an aerodynamic vane shape is formed to minimize pressure flow loss for core flow stream passage through the variable area exhaust mixer70. The trailing edge flap92is selectively opened to form a passage exhaust94from the respective strut flow passage82(also shown inFIGS. 4 and 5).

The trailing edge flap92may be hinged along an axis F with respect to one of the first and second walls84,86(FIG. 4) or, alternatively, from both of the first and second walls84,86to form as a split flap arrangement (FIG. 5). In these disclosed non-limiting embodiments, the axis F is generally transverse to the axis D and the longitudinal engine axis A. The multiple of doors78and respective trailing edge flaps92are selectively operable to form a relatively large area flowpath between the fan stream flow path56or58and the core flow path60for high bypass operations.

When open, the variable area exhaust mixer70substantially changes the area-ratio between the fan flow path(s)56,58and the core flow path60. Furthermore, the generally transverse arrangement of the multiple of doors78to the multiple of trailing edge flaps92of the variable area exhaust mixer70facilitates uniform mixture and redirection of the fan flow stream(s) from the fan flow path(s)56,58radially inward then axially aftward along the longitudinal engine axis A to provide mixing uniformity with minimum mixing pressure loss. The multiple of circumferentially arrayed vanes72further facilitate uniform radial mixing of the fan flow stream to increase propulsive efficiency as the relatively uniform mixing of the relatively cool air from the fan flow stream with the relatively hot core combustion products of the core flow stream downstream of the low pressure turbine section22provides increased propulsion efficiency and reduced exhaust jet noise.

In one operational example, the variable area exhaust mixer70is operable to change the area-ratio between the fan flow stream and the core flow stream by about 20%-50%. In other words, during high bypass operation, the variable area exhaust mixer70is opened (FIGS. 3, 4, 5) from a closed position (FIGS. 6 and 7) to increase the bypass ratio by about 20%-50%.

The multiple of doors78and the respective trailing edge flaps92of the variable area exhaust mixer70may be selectively actuated via electric actuators, pneumatic actuators, mechanical actuators, or combinations thereof to alter the bypass ratio during flight to match requirements. This facilitates efficient performance over a broad range of altitudes and flight conditions to generate high thrust for high-energy maneuvers yet optimize fuel efficiency for cruise and loiter operations.

The augmentor section26may be located downstream of the variable area exhaust mixer70, or alternatively, may be integrated into the respective multiple of circumferentially arrayed vanes72to selectively provide thrust augmentation with the oxygen-rich fan flow stream. In this disclosed non-limiting embodiment, one or more of the multiple of circumferentially arrayed vanes72may contain one or more spraybars100from a fuel manifold102within the tail cone74to selectively spray fuel for thrust augmentation through the first and/or second walls84,86. The relatively low velocity flow stream from the multiple of vanes72, in combination with their rear-facing trailing edges90thereof are readily configured to provide bluff body flame holders to generate a low velocity region in the exhaust flow stream to facilitate flame stability for the augmentor section26.

The variable area exhaust mixer70provides substantial benefits in fuel-burn, range, and performance by facilitation of an engine cycle with a variable bypass ratio that can be integrated with thrust augmentation features to provide an adaptive, multi-functional, variable exhaust systems for various propulsion systems. The variable area exhaust mixer70also facilitates noise reduction though a decrease in the exhaust jet temperature and velocity and efficient mixture of the fan and core flow streams with a significant range of variability in area ratio. The variable area exhaust mixer70is also compact and readily integrates with a turbine exhaust case and vehicle nozzle to reduce system weight, which otherwise trades with mixing efficiency and losses.

It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the engine but should not be considered otherwise limiting.