Multiple bypass-duct turbofan with annular flow plug nozzle and method of operating same

In a method of operating a propulsion nozzle for a gas turbine engine comprising a core engine, and two substantially coannular bypass flow ducts having a common wall therebetween, the steps of:

• passing separate subsonic flow streams through the coannular ducts;
• modulating the relative flow rates through the ducts at a common mixing plane using valve means disposed at the downstream end of the common wall;
• and
• passing the combined flows through a variable area throat independent of the core engine and partially defined by an articulated plug and a cooperating circumscribing shroud.

A propulsion nozzle for a multiple bypass duct gas turbine engine having a core engine, said nozzle comprising:

• an inner bypass flow duct partially circumscribing the core engine;
• an outer bypass flow duct partially circumscribing said inner bypass flow duct and separated therefrom by a common wall;
• variable position valve means disposed upon the downstream end of the common wall for modulating the relative flow rates through said inner and outer ducts;
• a translatable shroud;
• and
• an articulated annular plug, independent of the core engine, mounted within and cooperating with said shroud to define an exhaust duct therebetween having a throat and an exit, said exhaust duct disposed so as to receive flow from said inner and outer bypass ducts;
• wherein said articulated plug and said translatable shroud cooperate to modulate the throat area and the throat-to-exit area ratio as required.