Gas turbine engine with fan variable area nozzle, nacelle assembly and method of varying area of a fan nozzle

A high-bypass gas turbine engine comprising:

• a core engine defined about an axis, said core engine having a low pressure turbine with a pressure ratio that is greater than 5:1;
• a gear system driven by said core engine;
• a turbofan driven by said gear system about said axis said turbofan having a bypass ratio greater than (10:1);
• a core nacelle defined at least partially about said core engine;
• a fan nacelle mounted at least partially around said core nacelle to define a fan bypass flow path;
• and
• a louver system subdivided into multiple sectors, in communication with said fan bypass flow path and including an end segment of said fan nacelle, said louver system movable between a closed position and an open position to vary a fan nozzle exit area to adjust fan bypass air flow such that the angle of attack of turbofan fan blades are maintained close to design incidence for efficient engine operation.

A method of varying a fan nozzle exit area of a high-bypass gas turbine engine comprising the steps of:

• (A) positioning a louver system at an end segment of a fan nacelle and in communication with a fan bypass flow path said louver system including a multiple of sectors, each of said multiple of sectors including a multiple of louver slats with a first louver slat arranged forward of a second louver slat;
• (B) selectively varying a fan nozzle exit area in response to a flight condition;
• (C) adjusting fan bypass air flow such that the angle of attack of turbofan fan blades are maintained close to design incidence for efficient engine operation;
• and
• (D) moving said louver system between a closed position and an open position to vary the fan nozzle exit area.

A nacelle assembly for a high-bypass gas turbine engine comprising:

• a generally cylindrical core nacelle defined about an axis;
• a generally cylindrical fan nacelle mounted at least partially around said core nacelle to define a fan bypass flow path;
• and
• a louver system in communication with said fan bypass flow path and including an end segment of said fan nacelle, said louver system movable between a closed position and an open position to vary a fan nozzle exit area to adjust fan bypass air flow such that the angle of attack of turbofan fan blades are maintained close to design incidence for efficient engine operation, said louver system including multiple pivotable louver slats having an inner surface at said fan bypass flow path and an opposed, outer surface, and in said open position said pivotable louver slats are positioned to receive the fan bypass air flow over said inner surface and said outer surface.