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 defined 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 between 0.5 and 1.5.
1 . A gas turbine engine comprising:
a fan shaft driving a fan;
a plurality of gears in driving engagement with said fan shaft;
a first turbine section providing a drive input into said plurality of gears;
wherein a flexible connection connects said plurality of gears to be driven by said first turbine section, and said flexible connection having at least one of a flexible connection lateral stiffness and a flexible connection transverse stiffness that is less than 5% of a respective one of a gear mesh lateral stiffness and a gear mesh transverse stiffness of 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,
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 1.075.
2 . The gas turbine engine as set forth in claim 1 , wherein said plurality of gears provide an epicylic gear system, said 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 being less than 12% 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 has between three and six stages and said second turbine has two stages.
4 . The gas turbine engine as set for in claim 3 , wherein said second speed is more than twice said first speed.
5 . The gas turbine engine as set forth in claim 3 , wherein there being a flexible support to support said epicyclic gear system, said flexible support having a flexible support lateral stiffness and a flexible support transverse stiffness, a frame which supports said fan shaft, and at least one of said flexible support lateral stiffness and said flexible support transverse stiffness being less than 11% of a respective one of a frame lateral stiffness and a frame mesh transverse stiffness.
6 . The gas turbine engine as set forth in claim 5 , wherein a flexible connection connects a sun gear of said epicyclic gear system to be driven by said first turbine section, and said flexible connection having at least one of a flexible connection lateral stiffness and a flexible connection transverse stiffness that is less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness.
7 . The gas turbine engine as set forth in claim 5 , wherein a power 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 lbf/inch 3 , and less than or equal to 5.5 lbf/inch 3 .
8 . The gas turbine engine as set forth in claim 5 , wherein a bypass ratio is greater than or equal to 10.0, and a gear ratio of said plurality of gears is greater than 2.3.
9 . The gas turbine engine as set forth in claim 1 , wherein said first turbine has between three and six stages and said second turbine has two stages.
10 . The gas turbine engine as set forth in claim 9 , wherein a bypass ratio is greater than or equal to 10.0, and a gear ratio of said plurality of gears is greater than 2.3.
11 . The gas turbine engine as set forth in claim 10 , wherein there being a flexible support to support said epicyclic gear system, said flexible support having 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 being less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.
12 . The gas turbine engine as set for in claim 9 , wherein said second speed is more than twice said first speed.
13 . A gas turbine engine comprising:
a fan shaft driving a fan having fan blades;
a plurality of gears in driving engagement with said fan shaft; and
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,
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 1.075; and
wherein a power 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 lbf/inch 3 .
14 . The gas turbine engine as set forth in claim 13 , wherein said plurality of gears provide an epicyclic gear system, said epicyclic gear system including a ring gear having a ring gear lateral stiffness and a ring gear transverse stiffness and said epicyclic gear system having a gear mesh lateral stiffness and a gear mesh transverse stiffness, and 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.
15 . The gas turbine engine as set forth in claim 14 , wherein there being a flexible support to support said epicyclic gear system, said flexible support having 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 being less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.
16 . The gas turbine engine as set forth in claim 15 , wherein a low fan pressure ratio across the fan blades alone is less than 1.45.
17 . The gas turbine engine as set forth in claim 16 , wherein said first turbine has between three and six stages and said second turbine has two stages.
18 . The gas turbine engine as set forth in claim 17 , wherein a gear ratio of said epicyclic gear system is greater than 2.3.
19 . The gas turbine engine as set forth in claim 18 , wherein there is a frame which supports said fan shaft, 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 a frame lateral stiffness.
20 . The gas turbine engine as set for in claim 17 , wherein said second speed is more than twice said first speed.
21 . The gas turbine engine as set forth in claim 15 , 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 a frame lateral stiffness and a frame transverse stiffness of a frame which supports said fan shaft.
22 . The gas turbine engine as set forth in claim 21 , wherein a flexible connection connects a sun gear of said epicyclic gear system to be driven by said first turbine section, and a frame which supports said fan shaft, and said flexible connection having at least one of a flexible connection lateral stiffness and a flexible connection transverse stiffness that is less than 11% of a respective one of a frame lateral stiffness and a frame transverse stiffness.
23 . The gas turbine engine as set forth in claim 22 , wherein said power ratio being less than or equal to 5.5 lbf/inch 3 .
24 . The gas turbine engine as set forth in claim 22 , wherein said power ratio being greater than or equal to 4.0 lbf/inch 3 .
25 . The gas turbine engine as set forth in claim 13 , wherein said first turbine section having between three and six stages and said second turbine section having two stages.
26 . The gas turbine engine as set forth in claim 25 , wherein said plurality of gears provide an epicyclic gear system, said epicyclic gear system including a ring gear having a ring gear lateral stiffness and a ring gear transverse stiffness and said epicyclic gear system having a gear mesh lateral stiffness and a gear mesh transverse stiffness, and 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.
27 . The gas turbine engine as set forth in claim 26 , wherein there being a flexible support to support said epicyclic gear system, said flexible support having 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 being 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 frame which supports said fan shaft, and at least one of said flexible support lateral stiffness and said flexible support transverse stiffness being less than 11% of a respective one of a frame lateral stiffness.
29 . The gas turbine engine as set forth in claim 27 , wherein a flexible connection connects a sun gear of said epicyclic gear system to be driven by said first turbine section, and a frame which supports said fan shaft, and said flexible connection having at least one of a flexible connection lateral stiffness and a flexible connection transverse stiffness that is less than 11% of a respective one of a frame lateral stiffness and a frame transverse stiffness.
30 . The gas turbine engine as set forth in claim 29 , wherein said power ratio being less than or equal to 5.5 lbf/inch 3 .