The United States of America As Represented by the United States

The United States of America As Represented by the Administrator of the

Tom Foster

James Edward Johnson

Donald Patrick McHugh

Dan Joseph Rundell

Ralph Harold Brown

Roy Duncan Allan

A design technique, method and apparatus for controlling the bypass gas stream pressure and varying the bypass ratio of a mixed flow gas turbine engine in order to achieve improved performance. The disclosed preferred embodiments each include a unique mixing device for combining the core and bypass gas streams which includes means for varying the area at which the bypass stream is injected into the core stream. The variable area mixing device permits the static pressures of the core and bypass streams to be balanced prior to mixing at widely varying bypass stream dynamic pressure levels. The ability to balance the core and bypass stream static pressures at widely varying bypass stream dynamic pressures permits the mixed flow gas turbine engine of this invention to operate efficiently over a wide range of bypass ratios and further permits the dynamic pressure of the bypass stream to be maintained at a level which will keep the engine inlet airflow matched to an optimum design level throughout a wide range of engine thrust settings. To further assist in maintaining a static pressure balance between the core and bypass streams prior to mixing, the variable area mixing device may be provided with means to accelerate the bypass stream to supersonic velocities immediately prior to mixing combined with means to control the degree of expansion of the bypass stream after it has been accelerated to supersonic and before it is mixed with the core stream. To increase the flexibility in adjusting the dynamic pressure of the bypass stream and provide the potential for a relatively high thrust level without the use of an afterburner, the system may be modified by the use of a split fan section in conjunction with two concentric bypass ducts.

Variable mixer propulsion cycle

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.

Variable cycle gas turbine engines

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Cincinnati, OH, United States of America

Tom Foster