Gas turbine engine with low stage count low pressure turbine

Abstract

A gas turbine engine including 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 spool along the engine axis drives the gear train. The spool includes a downstream turbine having six or fewer stages. A fan is driven through the gear train by the downstream turbine. A pressure ratio across the fan is less than about 1.45. A fan variable area nozzle is axially movable relative to the fan nacelle to vary a fan nozzle exit area and adjust a pressure ratio of the fan bypass airflow during engine operation.

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 spool along said engine axis which drives said gear train, said spool includes a downstream turbine having six or fewer stages;   a fan driven through the gear train by the downstream turbine, wherein a pressure ratio across the fan is less than about 1.45; and   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 spool is a low spool. 
     
     
         3 . The engine as recited in  claim 1 , wherein said downstream turbine defines a pressure ratio that is greater than about five (5). 
     
     
         4 . The engine as recited in  claim 1 , wherein said downstream turbine defines a pressure ratio that is greater than five (5). 
     
     
         5 . The engine as recited in  claim 1 , wherein said fan bypass airflow defines a bypass ratio greater than about ten (10). 
     
     
         6 . The engine as recited in  claim 1 , wherein said fan bypass airflow defines a bypass ratio greater than ten (10). 
     
     
         7 . 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. 
     
     
         8 . The engine as recited in  claim 1 , wherein said gear train defines a gear reduction ratio of greater than or equal to 2.5. 
     
     
         9 . The engine as recited in  claim 1 , further comprising:
 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.   
     
     
         10 . The engine as recited in  claim 9 , wherein said controller is operable to reduce said fan nozzle exit area at a cruise flight condition. 
     
     
         11 . The engine as recited in  claim 9 , wherein said controller is operable to control said fan nozzle exit area to reduce a fan instability. 
     
     
         12 . The engine as recited in  claim 1 , wherein said fan variable area nozzle defines a trailing edge of said fan nacelle. 
     
     
         13 . The engine as recited in  claim 1 , wherein said gear train drives a fan within said fan nacelle. 
     
     
         14 . A gas turbine engine comprising:
 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 spool along said engine axis which drives said gear train, said spool includes a downstream turbine having six or fewer stages; and   a fan driven by said spool through said gear train, wherein said fan defines a fan bypass airflow having a bypass ratio greater than about ten (10) and a fan pressure ratio less than about 1.45.   
     
     
         15 . The engine as recited in  claim 14 , wherein said downstream turbine is a three (3) stage turbine. 
     
     
         16 . The engine as recited in  claim 14 , wherein said downstream turbine is a five (5) stage turbine. 
     
     
         17 . The engine as recited in  claim 14 , wherein said downstream turbine is a six (6) stage turbine. 
     
     
         18 . The engine as recited in  claim 14 , wherein said downstream turbine defines a pressure ratio that is greater than about five (5). 
     
     
         19 . The engine as recited in  claim 14 , wherein said gear train defines a gear reduction ratio of greater than or equal to about 2.5. 
     
     
         20 . The engine as recited in  claim 14 , wherein said downstream turbine defines a pressure ratio that is greater than five (5), said spool drives a fan through said gear train, said fan defines a fan bypass airflow having a bypass ratio greater than ten (10), and said gear train defines a gear reduction ratio of greater than or equal to 2.5. 
     
     
         21 . The gas turbine engine as recited in  claim 1 , wherein the fan includes a plurality of blades and a fan blade tip speed is less than 1150 ft/second. 
     
     
         22 . The gas turbine engine as recited in  claim 14 , wherein the fan includes a plurality of blades and a fan blade tip speed is than 1150 ft/second. 
     
     
         23 . The gas turbine engine as recited in  claim 14 , wherein there are three turbine rotors, and said downstream turbine is a most downstream of said three turbine rotors.