Geared turbofan gas turbine engine architecture
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. A speed reduction device such as an epicyclical gear assembly may be utilized to drive the fan section such that the fan section may rotate at a speed different than the turbine section so as to increase the overall propulsive efficiency of the engine. In such engine architectures, a shaft driven by one of the turbine sections provides an input to the epicyclical gear assembly that drives the fan section at a speed different than the turbine section such that both the turbine section and the fan section can rotate at closer to optimal speeds providing increased performance attributes and performance by desirable combinations of the disclosed features of the various components of the described and disclosed gas turbine engine.
1. A gas turbine engine comprising:
a fan including a plurality of fan blades rotatable about an axis, and a low fan pressure ration across the plurality of fan blades alone of less than 1.45;
a compressor section;
a combustor in fluid communication with the compressor section;
a turbine section in fluid communication with the combustor, the turbine section including a fan drive turbine and a second turbine, wherein the second turbine is disposed forward of the fan drive turbine and the fan drive turbine includes a plurality of turbine rotors with a ratio between the number of fan blades and the number of fan drive turbine rotors is between 2.5 and 8.5; and
a speed change system configured to be driven by the fan drive turbine to rotate the fan about the axis at a different speed than the fan drive turbine;
wherein the fan drive turbine has a first exit area and rotates at a first speed, the second turbine section has a second exit area and rotates at a second speed, which is faster than the first speed, said first and second speeds being redline speeds, a first performance quantity is defined as the product of the first speed squared and the first area, a second performance quantity is defined as the product of the second speed squared and the second area, and a performance ratio of the first performance quantity to the second performance quantity is greater than 0.5, and the performance ration is less than or equal to 1.5.
2. The engine as recited in claim 1 , wherein the speed change system comprises a gear reduction having a gear ratio greater than about 2.3.
3. The engine as recited in claim 2 , wherein the fan drive turbine has from three to six stages.
4. The engine as recited in claim 3 , wherein the fan has less than 18 of said fan blades and the second turbine has two stages.
5. The engine as recited in claim 4 , further comprising a frame structure positioned between the fan drive turbine and the second turbine, and a plurality of vanes associated with the frame structure.
6. The engine as recited in claim 3 , wherein the fan delivers a portion of air into a bypass duct, and a bypass ratio being defined as the portion of air delivered into the bypass duct divided by an amount of air delivered into the compressor section, with the bypass ratio being greater than 10.0.
7. The engine as recited in claim 6 , wherein the fan drive turbine includes an inlet having an inlet pressure, an outlet that is prior to any exhaust nozzle and having an outlet pressure, and a pressure ratio defined as a ratio of the inlet pressure to the outlet pressure, and wherein the pressure ratio of the fan drive turbine is greater than about 5.
8. The engine as recited in claim 7 , wherein the second turbine has two stages.
9. The engine as recited in claim 8 , wherein the fan has less than 18 of said fan blades.
10. The engine as recited in claim 9 , further comprising a low corrected fan tip speed less than about 1150 ft/second, wherein the low corrected fan tip speed is an actual fan tip speed divided by [(Tram ° R)/(518.7° R)] 0.5 , where T represents the ambient temperature in degrees Rankine.
11. The engine as recited in claim 10 , wherein the performance ratio is above or equal to about 0.8.
12. The engine as recited in claim 11 , wherein the performance ratio is above or equal to about 1.0.
13. The engine as recited in claim 1 , wherein the performance ratio is above or equal to about 0.8.
14. The engine as recited in claim 13 , wherein the performance ratio is above or equal to about 1.0.