Gas turbine engine with low stage count low pressure turbine

Abstract

A gas turbine engine includes a core nacelle defined about an engine axis. A fan nacelle is mounted at least partially around the core nacelle to define a fan bypass airflow path for a fan bypass airflow. A gear train is defined along an engine axis. The gear train defines a gear reduction ratio of greater than or equal to about 2.3. A fan drive turbine along the engine axis which drives the gear train. The fan drive turbine includes three to six (3-6) stages. A fan is configured for rotation within the fan nacelle for operation at a fan pressure ratio less than about 1.45. A fan variable area nozzle is axially movable relative to said fan nacelle to vary a fan nozzle exit area and adjust a pressure ratio of the fan bypass airflow during engine operation. A high bypass gas turbine engine is also disclosed.

1 . A gas turbine engine comprising:
 a core nacelle defined about an engine axis;   a fan nacelle mounted at least partially around said core nacelle to define a fan bypass airflow path for a fan bypass airflow;   a gear train defined along an engine axis, said gear train defines a gear reduction ratio of greater than or equal to about 2.3;   a fan drive turbine along said engine axis which drives said gear train, said fan drive turbine including three to six (3-6) stages; and   a fan configured for rotation within the fan nacelle for operation at a fan pressure ratio less than about 1.45,   a fan variable area nozzle axially movable relative to said fan nacelle to vary a fan nozzle exit area and adjust a pressure ratio of the fan bypass airflow during engine operation.   
     
     
         2 . The engine as recited in  claim 1 , wherein said fan drive turbine defines a pressure ratio that is greater than about five (5). 
     
     
         3 . The engine as recited in  claim 1 , wherein said fan drive turbine defines a pressure ratio that is greater than five (5). 
     
     
         4 . The engine as recited in  claim 1 , wherein said fan bypass airflow defines a bypass ratio greater than about ten (10). 
     
     
         5 . The engine as recited in  claim 1 , wherein said fan bypass airflow defines a bypass ratio greater than ten (10). 
     
     
         6 . The engine as recited in  claim 1 , wherein said gear train defines a gear reduction ratio of greater than or equal to about 2.5. 
     
     
         7 . The engine as recited in  claim 1 , wherein said gear train defines a gear reduction ratio of greater than or equal to 2.5. 
     
     
         8 . The engine as recited in  claim 1 , further comprising:
 a fan variable area nozzle axially movable relative to said fan nacelle to vary a fan nozzle exit area and to adjust a pressure ratio of the fan bypass airflow during engine operation; and   
       a controller operable to control said fan variable area nozzle to vary the fan nozzle exit area and adjust the pressure ratio of the fan bypass airflow. 
     
     
         9 . The engine as recited in  claim 8 , wherein said controller is operable to reduce said fan nozzle exit area at a cruise flight condition. 
     
     
         10 . The engine as recited in  claim 8 , wherein said controller is operable to control said fan nozzle exit area to reduce a fan instability. 
     
     
         11 . The engine as recited in  claim 8 , wherein said fan variable area nozzle defines a trailing edge of said fan nacelle. 
     
     
         12 . A high bypass gas turbine engine comprising:
 a core nacelle defined about an engine axis;   
       a fan nacelle mounted at least partially around said core nacelle to define a fan bypass airflow path for a fan bypass airflow;
 a gear train defined along an engine axis, said gear train defines a gear reduction ratio of greater than or equal to about 2.3; and 
 a fan drive turbine rotatable about said engine axis which drives said gear train, said fan drive turbine including three to six (3-6) stages; and 
 a fan section configured for operation at a fan pressure ratio less than about 1.45, wherein said fan bypass airflow includes a bypass ratio greater than about (10). 
 
     
     
         13 . The engine as recited in  claim 12 , wherein said fan drive turbine is a three (3) stage turbine. 
     
     
         14 . The engine as recited in  claim 12 , wherein said fan drive turbine is a five (5) stage turbine. 
     
     
         15 . The engine as recited in  claim 12 , wherein said fan drive turbine is a six (6) stage turbine. 
     
     
         16 . The engine as recited in  claim 12 , wherein said fan drive turbine defines a pressure ratio that is greater than about five (5). 
     
     
         17 . The engine as recited in  claim 12 , wherein said gear train defines a gear reduction ratio of greater than or equal to about 2.5. 
     
     
         18 . The engine as recited in  claim 12 , wherein said fan drive turbine defines a pressure ratio that is greater than five (5), said fan defines a fan pressure ratio less than about 1.45, and said gear train defines a gear reduction ratio of greater than or equal to 2.5. 
     
     
         19 . The engine as recited in  claim 12 , wherein there are three turbine rotors, with said fan drive turbine being the most downstream of said three turbine rotors.