Geared Architecture for High Speed and Small Volume Fan Drive Turbine

Abstract

A gas turbine engine includes a gear system that provides a speed reduction between a fan drive turbine and a fan rotor. Aspects of the gear system are provided with some flexibility. The fan drive turbine has a first exit area and rotates at a first speed. A second turbine section has a second exit area and rotates at a second speed, which is faster than said first speed. A performance quantity can be defined for both turbine sections as the products of the respective areas and respective speeds squared. A performance quantity ratio of the performance quantity for the fan drive turbine to the performance quantity for the second turbine section is relatively high.

1 . A gas turbine engine comprising:
 a fan shaft driving a fan having fan blades;   a frame which supports said fan shaft having a frame lateral stiffness and a frame transverse stiffness;   a plurality of gears in driving engagement with said fan shaft;   a flexible support which supports said plurality of gears, said flexible support having at least one of a flexible support lateral stiffness and a flexible support transverse stiffness that is less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness;   a first turbine section providing a drive input into said plurality of gears;   a second turbine section, and
 wherein said first turbine section has a first exit area at a first exit point and rotates at a first speed, 
 wherein said second turbine section has a second exit area at a second exit point and rotates at a second speed, which is faster than said first speed 
 wherein a first performance quantity is defined as the product of said first speed squared and said first area, 
 wherein a second performance quantity is defined as the product of said second speed squared and said second area, 
 a performance quantity ratio of said first performance quantity to said second performance quantity is greater than or equal to 0.5 and less than or equal to 1.5; and 
 a fan section including said fan is configured to include a low fan pressure ratio of less than 1.45 measured across said fan blades alone. 
   
     
     
         2 . The gas turbine engine as set forth in  claim 1 , wherein said plurality of gears includes a gear mesh, said gear mesh having a gear mesh lateral stiffness and a gear mesh transverse stiffness, and at least one of said flexible support lateral stiffness and said flexible support transverse stiffness is less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness. 
     
     
         3 . The gas turbine engine as set forth in  claim 2 , wherein said first turbine section includes a first turbine having an inlet, an outlet, and a first turbine pressure ratio greater than 5, wherein said first turbine pressure ratio is a ratio of a pressure measured prior to said inlet as related to a pressure at said outlet and prior to any exhaust nozzle. 
     
     
         4 . The gas turbine engine as set forth in  claim 3 , wherein said performance quantity is greater than or equal to 0.8, said second speed is faster than said first speed, and said plurality of gears is an epicyclic gear system including a ring gear having a ring gear lateral stiffness and a ring gear transverse stiffness and at least one of said ring gear lateral stiffness and said ring gear transverse stiffness is less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness. 
     
     
         5 . The gas turbine engine as set forth in  claim 4 , including a ratio of a flat-rated Sea Level Take-Off thrust provided by said engine in lbf, to a volume of a turbine section including both said first and second turbine sections in inch 3  being greater than or equal to 4.0 lbf/inch 3 . 
     
     
         6 . The gas turbine engine as set forth in  claim 5 , wherein both said flexible support transverse stiffness and said flexible support lateral stiffness are less than 11% of a respective one of said frame transverse stiffness and said frame lateral stiffness. 
     
     
         7 . The gas turbine engine as set forth in  claim 6 , wherein said fan section has a low corrected fan tip speed less than 1,150 ft/sec, wherein said low corrected fan tip speed is an actual fan tip speed divided by [(Tram° R)/(518.7° R)] 0.5 . 
     
     
         8 . The gas turbine engine as set forth in  claim 7 , wherein both said ring gear lateral stiffness and said ring gear transverse stiffness are less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness, and wherein said low fan pressure ratio is measured at cruise at 0.8 Mach and 35,000 feet. 
     
     
         9 . The gas turbine engine as set forth in  claim 1 , wherein a mid-turbine frame is positioned between said first and second turbine sections, and includes a plurality of airfoils positioned in a flow path. 
     
     
         10 . The gas turbine engine as set forth in  claim 1 , wherein said plurality of gears includes a gear mesh, said gear mesh having a gear mesh lateral stiffness and a gear mesh transverse stiffness, and at least one of said flexible support lateral stiffness and said flexible support transverse stiffness being less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness. 
     
     
         11 . The gas turbine engine as set forth in  claim 10 , including a ratio of a flat-rated Sea Level Take-Off thrust provided by said engine in lbf, to a volume of a turbine section including both said first and second turbine sections in inch 3  being greater than or equal to 1.5 and less than or equal to 5.5 lbf/inch 3 . 
     
     
         12 . The gas turbine engine as set forth in  claim 10 , including a ratio of a flat-rated Sea Level Take-Off thrust provided by said engine in lbf, to a volume of a turbine section including both said first and second turbine sections in inch 3  being greater than or equal to 4.0 lbf/inch 3 . 
     
     
         13 . The gas turbine engine as set forth in  claim 10 , wherein said plurality of gears is an epicyclic gear system including a ring gear having a ring gear lateral stiffness and a ring gear transverse stiffness, at least one of said ring gear lateral stiffness and said ring gear transverse stiffness being less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness. 
     
     
         14 . The gas turbine engine as set forth in  claim 13 , wherein said fan section has a low corrected fan tip speed less than 1,150 ft/sec, wherein said low corrected fan tip speed is an actual fan tip speed divided by [(Tram° R)/(518.7° R)] 0.5 . 
     
     
         15 . The gas turbine engine as set forth in  claim 14 , further comprising a bypass ratio greater than 10. 
     
     
         16 . The gas turbine engine as set forth in  claim 13 , wherein said low fan pressure ratio is measured at cruise at 0.8 Mach and 35,000 feet, said first turbine section includes an inlet, an outlet, and a first turbine section pressure ratio greater than 5, and wherein said first turbine section pressure ratio is a ratio of a pressure measured prior to said inlet as related to a pressure at said outlet and prior to any exhaust nozzle. 
     
     
         17 . The gas turbine engine as set forth in  claim 16 , wherein a flexible coupling connects a sun gear in said epicyclic gear system to be driven by said first turbine section, and said flexible coupling having at least one of a flexible coupling transverse stiffness and a flexible coupling lateral stiffness that is less than 5% of a respective one of said gear mesh transverse stiffness and said gear mesh lateral stiffness. 
     
     
         18 . The gas turbine engine as set forth in  claim 16 , wherein said performance quantity ratio is less than or equal to 1.075. 
     
     
         19 . The gas turbine engine as set forth in  claim 18 , wherein both said flexible support transverse stiffness and said flexible support lateral stiffness are less than 11% of a respective one of said frame transverse stiffness and said frame lateral stiffness. 
     
     
         20 . A gas turbine engine comprising:
 a fan shaft driving a fan;   an epicyclic gear system in driving engagement with said fan shaft and including a plurality of gears having a gear mesh lateral stiffness and a gear mesh transverse stiffness;   said epicyclic gear system including a ring gear having a ring gear lateral stiffness and a ring gear transverse stiffness, at least one of said ring gear lateral stiffness and said ring gear transverse stiffness being less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness;   a frame supports said fan shaft, the frame having a frame lateral stiffness and a frame transverse stiffness;   a flexible support supports said epicyclic gear system, said flexible support having a flexible support lateral stiffness and a flexible support transverse stiffness, at least one of said flexible support lateral stiffness and said flexible support transverse stiffness being less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness;   at least one of said flexible support lateral stiffness and said flexible support transverse stiffness being less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness;   a first turbine section providing a drive input into said epicyclic gear system;   a second turbine section,
 wherein said first turbine section has a first exit area at a first exit point and rotates at a first speed, 
 wherein said second turbine section has a second exit area at a second exit point and rotates at a second speed, which is faster than said first speed, 
 wherein a first performance quantity is defined as the product of said first speed squared and said first area, 
 wherein a second performance quantity is defined as the product of said second speed squared and said second area, 
 wherein a performance quantity ratio of the first performance quantity to said second performance quantity is between 0.5 and 1.5; and 
   a bypass ratio greater than 10.   
     
     
         21 . The gas turbine engine as set forth in  claim 20 , wherein said performance quantity ratio is greater than or equal to 0.8, and both said flexible support lateral stiffness and said flexible support transverse stiffness are less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness. 
     
     
         22 . The gas turbine engine as set forth in  claim 21 , including a ratio of a flat-rated Sea Level Take-Off thrust provided by said engine in lbf, to a volume of a turbine section including both said first and second turbine sections in inch 3  being greater than or equal to 4.0 lbf/inch 3 . 
     
     
         23 . The gas turbine engine as set forth in  claim 22 , wherein a flexible coupling connects a sun gear of said epicyclic gear system to be driven by said first turbine section, and at least one of said flexible coupling transverse stiffness and said flexible coupling lateral stiffness that is less than 5% of a respective one of said gear mesh transverse stiffness and said gear mesh lateral stiffness. 
     
     
         24 . A gas turbine engine comprising:
 a fan shaft driving a fan having fan blades;   an epicyclic gear system in driving engagement with said fan shaft and including a plurality of gears having a gear mesh lateral stiffness and a gear mesh transverse stiffness;   said epicyclic gear system including a ring gear having a ring gear lateral stiffness and a ring gear transverse stiffness, at least one of said ring gear lateral stiffness and said ring gear transverse stiffness being less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness;   a first turbine section providing a drive input into said epicyclic gear system;   a second turbine section,
 wherein said first turbine section has a first exit area at a first exit point and rotates at a first speed, 
 wherein said second turbine section has a second exit area at a second exit point and rotates at a second speed, which is faster than said first speed, 
 wherein a first performance quantity is defined as the product of said first speed squared and said first area, 
 wherein a second performance quantity is defined as the product of said second speed squared and said second area, 
 wherein a performance quantity ratio of said first performance quantity to said second performance quantity is between 0.5 and 1.5; and 
   a bypass ratio greater than 10.   
     
     
         25 . The gas turbine engine as set forth in  claim 24 , including a ratio of a flat-rated Sea Level Take-Off thrust provided by said engine in lbf, to a volume of a turbine section including both said first and second turbine sections in inch 3  being greater than or equal to 1.5 and less than or equal to 5.5 lbf/inch 3 . 
     
     
         26 . The gas turbine engine as set forth in  claim 25 , further comprising a frame that supports said fan shaft and a flexible support that supports said epicyclic gear system, said flexible support having at least one of a flexible support lateral stiffness and a flexible support transverse stiffness that is less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness. 
     
     
         27 . The gas turbine engine as set forth in  claim 26 , wherein said performance quantity ratio is less than or equal to 1.075. 
     
     
         28 . The gas turbine engine set forth in  claim 26 , wherein a fan section including said fan is configured to include a low fan pressure ratio of less than 1.45 at cruise at 0.8 mach and 35,000 feet, said low fan pressure ratio measured across said fan blades alone. 
     
     
         29 . The gas turbine engine as set forth in  claim 28 , wherein both said flexible support transverse stiffness and said flexible support lateral stiffness are less than 8% of a respective one of said gear mesh transverse stiffness and said gear mesh lateral stiffness. 
     
     
         30 . The gas turbine engine as set forth in  claim 29 , wherein said fan section has a low corrected fan tip speed less than 1,150 ft/sec, wherein said low corrected fan tip speed is an actual fan tip speed divided by [(Tram° R)/(518.7° R)] 0.5 .