Variable mixer propulsion cycle

Abstract

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.