Gas turbine engine with fan variable area nozzle for low fan pressure ratio

Abstract

A nacelle assembly for a high-bypass gas turbine engine includes a fan variable area nozzle movable relative a fan nacelle to vary a fan nozzle exit area and adjust a pressure ratio of the fan bypass airflow during engine operation.

What is claimed is: 
     
         1 . A nacelle assembly for a high-bypass gas turbine engine comprising:
 a core nacelle defined about an engine centerline axis;   a fan nacelle mounted at least partially around said core nacelle to define a fan bypass flow path for a fan bypass airflow; and   a fan variable area nozzle movable relative said fan nacelle to vary a fan nozzle exit area and adjust a fan pressure ratio of the fan bypass airflow during engine operation, said fan pressure ratio less than about 1.45.   
     
     
         2 . The assembly as recited in  claim 1 , further comprising a controller operable to control said fan variable area nozzle to vary said fan nozzle exit area and adjust said fan pressure ratio. 
     
     
         3 . The assembly as recited in  claim 2 , wherein said controller is operable to reduce said fan nozzle exit area at a cruise flight condition. 
     
     
         4 . The assembly as recited in  claim 2 , wherein said controller is operable to control said fan nozzle exit area to reduce a fan instability. 
     
     
         5 . The assembly as recited in  claim 1 , wherein said fan variable area nozzle defines a trailing edge of said fan nacelle. 
     
     
         6 . The assembly as recited in  claim 1 , further comprising a controller operable to axially move said fan variable area nozzle to vary said fan nozzle exit area in response to a flight condition. 
     
     
         7 . The assembly as recited in  claim 1 , further comprising a gear system driven by a core engine within said core nacelle to drive a fan within said fan nacelle. 
     
     
         8 . The assembly as recited in  claim 7 , wherein said fan defines a corrected fan tip speed less than about 1150 ft/second. 
     
     
         9 . The assembly as recited in  claim 7 , wherein said core engine includes a low pressure turbine which defines a low pressure turbine pressure ratio that is greater than about five (5). 
     
     
         10 . The assembly as recited in  claim 7 , wherein said core engine includes a low pressure turbine which defines a low pressure turbine pressure ratio that is greater than five (5). 
     
     
         11 . The assembly as recited in  claim 1 , further comprising a gear system driven by a core engine within the core nacelle to drive a fan within the fan nacelle, said gear system defines a gear reduction ratio of greater than or equal to about 2.3. 
     
     
         12 . The assembly as recited in  claim 1 , further comprising a gear system driven by a core engine within said core nacelle to drive a fan within said fan nacelle, said gear system defines a gear reduction ratio of greater than or equal to about 2.5. 
     
     
         13 . The assembly as recited in  claim 1 , wherein said fan bypass airflow defines a bypass ratio greater than about six (6). 
     
     
         14 . The assembly as recited in  claim 1 , wherein said fan bypass airflow defines a bypass ratio greater than about ten (10). 
     
     
         15 . The assembly as recited in  claim 1 , wherein said fan bypass airflow defines a bypass ratio greater than ten (10).