Geared Architecture for High Speed and Small Volume Fan Drive Turbine
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, said frame having a frame lateral stiffness and a frame transverse stiffness;
a plurality of gears which drive said fan shaft;
a flexible support which supports said plurality of gears and has a flexible support lateral stiffness and a flexible support transverse stiffness, and at least one of said flexible support lateral stiffness and said flexible support transverse stiffness 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, said first and second speeds being redline speeds,
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 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 a mid-turbine frame is positioned between said first and second turbine sections, and includes a plurality of airfoils positioned in a flow path.
3 . The gas turbine engine as set forth in claim 1 , wherein said plurality of gears 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.
4 . The gas turbine engine as set forth in claim 3 , 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.
5 . The gas turbine engine as set forth in claim 4 , wherein said plurality of gears being an epicyclic gear system including a ring gear having at least one of a ring gear lateral stiffness and a ring gear transverse stiffness that is less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.
6 . The gas turbine engine as set forth in claim 5 , 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 .
7 . The gas turbine engine as set forth in claim 6 , wherein said flexible support lateral stiffness and said flexible support transverse stiffness both are less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness.
8 . The gas turbine engine as set forth in claim 7 , 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 .
9 . The gas turbine engine as set forth in claim 8 , wherein said ring gear lateral stiffness and said ring gear transverse stiffness both are less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.
10 . The gas turbine engine as set forth in claim 9 , wherein said performance quantity ratio is less than or equal to 1.075.
11 . The gas turbine engine as set forth in claim 1 , 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 .
12 . The gas turbine engine as set forth in claim 11 , wherein said plurality of gears being an epicyclic gear system and having a gear mesh lateral stiffness and a gear mesh transverse stiffness, and including a ring gear having at least one of a ring gear lateral stiffness and a ring gear transverse stiffness that is less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.
13 . The gas turbine engine as set forth in claim 12 , wherein said performance quantity ratio is less than or equal to 1.075.
14 . A gas turbine engine comprising:
a fan shaft driving a fan having fan blades;
a plurality of gears which drive said fan shaft and having a gear mesh lateral stiffness and a gear mesh transverse stiffness;
a flexible support which supports said plurality of gears, and has a flexible support lateral stiffness and a flexible support 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;
a first turbine section providing a drive input into said plurality of gears;
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, said first and second speeds being redline speeds,
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.
15 . The gas turbine engine as set forth in claim 14 , 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 .
16 . The gas turbine engine as set forth in claim 15 , further comprising a frame that supports said fan shaft, said frame having a frame lateral stiffness and a frame transverse stiffness, and wherein at least one of said flexible support lateral stiffness and said flexible support transverse stiffness is less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness.
17 . The gas turbine engine as set forth in claim 16 , wherein said performance quantity ratio is less than or equal to 1.075.
18 . The gas turbine engine set forth in claim 16 , wherein a fan section including said fan is configured to include a low fan pressure ratio of less than 1.45, said low fan pressure ratio measured across said fan blades alone.
19 . The gas turbine engine as set forth in claim 18 , 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, wherein 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.
20 . The gas turbine engine as set forth in claim 19 , 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 .
21 . The gas turbine engine as set forth in claim 20 , 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.
22 . The gas turbine engine as set forth in claim 14 , 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 said plurality of gears is an epicyclic gear system having a ring gear with 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.
24 . The gas turbine engine as set forth in claim 23 , wherein 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.
25 . The gas turbine engine as set forth in claim 24 , wherein both said flexible support lateral stiffness and said flexible support transverse stiffness are less than 11% of a respective one of a frame lateral stiffness and a frame transverse stiffness of a frame that supports said fan shaft.
26 . The gas turbine engine as set forth in claim 25 , 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 .
27 . The gas turbine engine as set forth in claim 25 , wherein both said flexible support lateral stiffness and said flexible support transverse stiffness are less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness, and less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.
28 . The gas turbine engine as set forth in claim 27 , wherein a flexible coupling connects a sun gear of said epicyclic gear system to be driven by said first turbine section, and said flexible coupling having at least one of a flexible coupling lateral stiffness and a flexible coupling transverse stiffness that is less than 5% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.
29 . The gas turbine engine as set forth in claim 14 , wherein said plurality of gears is an epicyclic gear system including a ring gear, wherein at least one of a ring gear lateral stiffness and a ring gear transverse stiffness are less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.
30 . The gas turbine engine as set forth in claim 14 , wherein said performance quantity ratio is less than or equal to 1.075.