Abstract: A third stream duct producing a third air stream at reduced pressure that is exhausted through a separate nozzle that is concentric with the main or primary engine nozzle. The third stream exhaust air from the separate concentric nozzle is exhausted to a location at which pressure is ambient or sub-ambient. The location at which the third stream air is exhausted contributes to the thrust of the aircraft. The airstream from the third air duct is exhausted through an exhaust nozzle of the third duct that is positioned at the interface between the aft of the airframe and the leading edge of the engine outer flaps. This location is a low pressure region that has a recirculation zone. The exhaust of third stream air to this low pressure region substantially reduces or eliminates this recirculation zone and associated boat tail drag, thereby improving the efficiency of the engine.

Abstract: An exhaust system for a variable cycle aircraft engine. The exhaust system comprises a core exhaust for bypass air and hot gases of combustion. The core exhaust includes a convergent-divergent nozzle. The convergent-divergent nozzle is formed from a plurality of flaps and seals. The exhaust system comprises a third air duct for a third stream of air. The third stream of air is selectively exhausted from the third duct through a secondary nozzle or divergent slots in the convergent-divergent nozzle, or both depending upon the flight mode. A diverter valve is positioned in the third stream duct to selectively control the flow of third stream air through the secondary nozzle, the divergent slots and combinations thereof.