US 4,064,692 AGranted

Variable cycle gas turbine engines

AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration

InventorsJames Edward Johnson, Tom Foster, Roy Duncan Allan

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Abstract

A design technique, method, and apparatus for varying the bypass ratio and modulating the flow of a gas turbine engine of the bypass type in order to achieve improved mixed mission performance. The disclosed preferred embodiments each include a gas flow control system for management of core and bypass stream pressure comprising diverter valve means downstream of the core engine to selectively mix or separate the core and bypass exhaust streams. The flow control system may also include variable geometry means for maintaining the engine inlet airflow at a matched design level at all flight velocities. Each preferred embodiment thus may be converted from a high specific thrust mixed flow cycle at supersonic velocities to a lower specific thrust separated flow turbofan system at subsonic velocities with a high degree of flow variability in each mode of operation, wherein the engine inlet airflow may be maintained at a matched design level at all engine velocities. To further improve flow flexibility and assist in maintaining the engine inlet airflow matched to a design level throughout a variable velocity range, the flow control system may include a split fan in conjunction with two concentric bypass ducts. The disclosed variable cycle engine techniques, methods, and apparatus result in significantly reduced inlet and after-body drag levels and result in significantly improved installed fuel consumption for mixed mission aircraft.

Claims11

Dependent claims

A gas turbine engine comprising:

an inner nacelle circumscribing a core engine, low pressure turbine and afterburner in respective serial flow relation wherein the inner nacelle extends downstream of the afterburner to define an inner nozzle for exhausting the core engine gas flow;
an outer nacelle circumscribing the inner nacelle and spaced apart therefrom to form an outer bypass duct around the core engine and wherein the outer nacelle extends upstream of the inner nacelle to form an inlet for the engine and downstream of the inner nozzle to form an outer nozzle for exhausting the bypass and core engine gas flows;
a fan disposed in the inlet upstream of the core engine and driven by the low pressure turbine for compressing inlet gas flow to the bypass duct and core engine;
flow passage means disposed through the inner nacelle intermediate the low pressure turbine and afterburner for injecting the bypass duct flow into the core engine exhaust such that the combined flows are directed through the afterburner;
valve means for selectively obtruding and unobtruding the flow passage means whereby the engine may be operated as a high bypass turbofan when said flow passage means is obtruded and as low bypass mixed flow augmented turbojet when said flow passage means is unobtruded, and
flap means pivotally hinged to the downstream end of the inner nacelle for simultaneously varying the area of the inner exhaust nozzle and the exhaust area of the other bypass duct, wherein the flap means is movable to a position to abut the outer nacelle such that gas flow through the outer bypass duct is obtruded.

3 more elements

Dependencies are inferred from the claim text.