Turbine section of high bypass turbofan
A turbofan engine has an engine case and a gaspath through the engine case. A fan has a circumferential array of fan blades. The engine further has a compressor, a combustor, a gas generating turbine, and a low pressure turbine section. A speed reduction mechanism couples the low pressure turbine section to the fan. A bypass area ratio is greater than about 6.0. The low pressure turbine section airfoil count to bypass area ratio is below about 170.
1. A turbofan engine comprising:
an engine case;
a gaspath through the engine case;
a fan rotatable about an engine longitudinal axis having a circumferential array of fan blades;
a compressor in fluid communication with the fan, the compressor including a first compressor section and a second compressor section, the second compressor section including a second compressor section inlet with a second compressor section inlet annulus area;
a fan duct including a fan duct annulus area outboard of the second compressor section inlet, wherein a ratio of the fan duct annulus area to the second compressor section inlet annulus area defines a bypass area ratio;
a combustor in fluid communication with the compressor;
a turbine in fluid communication with the combustor, the turbine having a two-stage first turbine section coupled to drive the first compressor section, and a four-stage second turbine section coupled to drive the second compressor section; and
a speed reduction mechanism coupling the four-stage second turbine section to the fan, the speed reduction mechanism comprising a planetary gearbox coupled to the fan and rotatable by the second turbine section to enable the second turbine section to rotate faster than the fan, the planetary gearbox having a speed reduction ratio between 2:1 and 13:1, wherein the planetary gearbox is axially forward of the second compressor section, wherein:
a ratio of a second turbine section airfoil count to the bypass area ratio is less than 170 and a ratio of a maximum gaspath radius along the second turbine section to a maximum radius of the fan is greater than or equal to 0.35 and is less than 0.50.
2. The engine of claim 1 wherein:
the bypass area ratio is between about 8.0 and about 20.0.
3. The engine of claim 2 further comprising:
a fan case and vanes, the fan case encircling the fan blades radially outboard of the engine case and supported by vanes.
4. The engine of claim 3 wherein:
an airfoil count of the second turbine section is below about 1600.
5. The engine of claim 1 wherein:
said ratio of the second turbine section airfoil count to bypass area ratio is between about 10 and about 150.
6. The engine of claim 5 wherein:
there are no additional compressor or turbine sections.
7. The engine of claim 6 wherein:
blades of the second compressor section and the second turbine section share a shaft; and
the speed reduction mechanism couples the shaft to a fan shaft to drive the fan with a speed reduction.
8. The engine of claim 7 wherein:
the airfoil count of the second turbine section is below about 1600.
9. The engine of claim 1 in combination with a mounting arrangement wherein an aft mount reacts at least a thrust load.
10. The engine of claim 9 wherein:
the second turbine section has blade stages interspersed with vane stages.
11. The engine as recited in claim 7 , wherein the first compressor section is a four-stage compressor section and the second compressor section is a nine-stage compressor section.