Gas turbine engine with low stage count low pressure turbine

Abstract

A gas turbine engine according to an example of the present disclosure includes, among other things, a fan section, a first compressor section including three (3) or more stages, a second compressor section including between eight (8) and thirteen (13) stages, and a first turbine section operable for driving the first compressor section, the first turbine section including between three (3) and six (6) stages, a second turbine section operable for driving the second compressor section, and a gear train defined along an engine centerline axis. One of the first turbine section and the second turbine section is operable to drive the fan section through the gear train.

What is claimed is: 
     
         1 . A gas turbine engine comprising:
 a fan section;   a first compressor section including three (3) or more stages;   a second compressor section including between eight (8) and thirteen (13) stages;   a first turbine section operable for driving the first compressor section, the first turbine section including between three (3) and six (6) stages;   a second turbine section operable for driving the second compressor section; and   a gear train defined along an engine centerline axis, wherein one of the first turbine section and the second turbine section is operable to drive the fan section through the gear train.   
     
     
         2 . The engine as recited in  claim 1 , wherein the first turbine section includes three (3) stages. 
     
     
         3 . The engine as recited in  claim 2 , wherein the first turbine defines a pressure ratio that is greater than about 5.0. 
     
     
         4 . The engine as recited in  claim 1 , including a fan case circumscribing the fan section that defines a fan bypass airflow, and wherein a bypass ratio of the engine is greater than about 10.0. 
     
     
         5 . The engine as recited in  claim 1 , wherein said gear train defines a gear reduction ratio of greater than about 2.3. 
     
     
         6 . The gas turbine engine as set forth in  claim 1 , further comprising a fan variable area nozzle to vary a fan nozzle exit area and adjust a fan pressure ratio of fan bypass airflow of said fan section during engine operation. 
     
     
         7 . The engine as recited in  claim 6 , further comprising:
 a controller operable to control said fan variable area nozzle to vary a fan nozzle exit area and adjust the fan pressure ratio of the fan bypass airflow.   
     
     
         8 . The engine as recited in  claim 7 , wherein said controller is operable to reduce said fan nozzle exit area at a cruise flight condition. 
     
     
         9 . The engine as recited in  claim 7 , wherein said controller is operable to control said fan nozzle exit area to reduce a fan instability. 
     
     
         10 . The engine as recited in  claim 6 , wherein said fan variable area nozzle defines a trailing edge of a fan nacelle. 
     
     
         11 . The gas turbine engine as recited in  claim 1 , wherein the second turbine section includes two (2) stages. 
     
     
         12 . The gas turbine engine as recited in  claim 11 , wherein the gear train comprises an epicyclic gear train with a gear reduction of greater than about 2.3:1. 
     
     
         13 . 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. 
     
     
         14 . The gas turbine engine as recited in  claim 13 , wherein the engine has a bypass ratio of greater than about 10.0. 
     
     
         15 . The gas turbine engine as recited in  claim 14 , wherein the fan section includes a plurality of fan blades and a fan pressure ratio across the plurality of fan blades is less than about 1.45. 
     
     
         16 . The gas turbine engine as recited in  claim 15 , wherein a corrected fan tip speed of the plurality of fan blades is less than about 1150 ft/second. 
     
     
         17 . The gas turbine engine as recited in  claim 15 , wherein the fan blades are mounted to a fan rotor and the fan rotor is supported by a dual bearing. 
     
     
         18 . The engine as recited in  claim 15 , wherein the first turbine section defines a pressure ratio that is greater than about 5.0. 
     
     
         19 . The engine as recited in  claim 1 , wherein said first turbine section is one of three turbine rotors, while said second turbine section and another one of said turbine rotors each drives a compressor section. 
     
     
         20 . The engine as recited in  claim 19 , wherein said first turbine section drives a compressor section. 
     
     
         21 . The engine as recited in  claim 20 , wherein said gear train is positioned intermediate said compressor section driven by said first turbine section and said fan section. 
     
     
         22 . The engine as recited in  claim 20 , wherein said gear train is positioned intermediate said first turbine section and said compressor section driven by said first turbine section.