Methods and apparatus for assembling a gas turbine engine
Methods and apparatus for assembling a gas turbine engine are provided. The method includes coupling a first turbine shaft that includes m rows of turbine blades within the gas turbine such that the first turbine shaft is rotatable in a first direction, and coupling a second turbine shaft that includes n rows of turbine blades within the gas turbine such that the second turbine shaft is rotatable in a second direction wherein a torque split between the first and second turbine shafts is substantially proportional to the number of rows of turbine blades on each shaft relative to a total number of rows of blades on both shafts, and wherein m and n are selected to provide a torque split between the first turbine shaft and second turbine shaft of greater than about 1.2:1.
1. A method of assembling a gas turbine engine, said method comprising:
coupling a first turbine shaft that includes m rows of first turbine blades within the gas turbine such that the first turbine shaft is rotatable in a first direction; and
coupling a second turbine shaft that includes n rows of second turbine blades within the gas turbine such that the second turbine shaft is rotatable in a second direction wherein a torque split between the first and second turbine shafts is substantially proportional to a number of rows of turbine blades on each shaft relative to a total number of rows of blades on both shafts, wherein m represents the number of first rows of turbine blades and n represents the number of second rows of turbine blades, and wherein m and n are selected to provide a torque split between the first low pressure turbine shaft and second low pressure turbine shaft of greater than about 1.2:1.
2. A method in accordance with claim 1 wherein m and n are selected to provide a torque split between the first low-pressure turbine shaft and second low-pressure turbine shaft of greater than 1.5 to 1.
3. A method in accordance with claim 1 wherein m and n are selected to provide a torque split between the first low-pressure turbine shaft and second low-pressure turbine shaft of greater than 2.0 to 1.
4. A method in accordance with claim 1 further comprising providing at least one row of nonrotating stator blades adjacent at least one of a portion of the m rows of turbine blades and a portion of the n rows of turbine blades.
5. A method in accordance with claim 1 further comprising interdigitating at least a portion of the m rows of turbine blades and a portion of the n rows of turbine blades.
6. A method in accordance with claim 1 further comprising interdigitating at least a portion of the m rows of turbine blades and at least one row of nonrotating stator blades.
7. A method in accordance with claim 1 further comprising interdigitating at least a portion of the n rows of turbine blades and at least one row of nonrotating stator blades.
8. A gas turbine engine assembly comprising:
a compressor;
a high pressure turbine coupled to said compressor by a rotor shaft; and
a low pressure turbine comprising at least one row of turbine stator blades spaced circumferentially apart and defining at least a portion of a flowpath extending through said low pressure turbine, said low pressure turbine further comprising a first rotor shaft coaxially aligned about a second rotor shaft, said first rotor shaft comprising m first rows of turbine blades, said second rotor shaft comprising n second rows of turbine blades, wherein m represents the number of first rows of turbine blades, n represents the number of second rows of turbine blades, and m and n are a different number with respect to each other, wherein at least a portion of said n second rows of turbine blades are interdigitated with at least a portion of said m first rows of turbine blades, said first rotor shaft rotatably coupled to a first compressor, said second rotor shaft rotatably coupled to a second compressor, and wherein m and n are selected to provide a torque split between the first low pressure turbine shaft and second low pressure turbine shaft of greater than about 1.2:1.
9. A gas turbine engine turbine assembly in accordance with claim 8 wherein a portion of said m first rows of turbine blades are interdigitated with said at least one row of stator blades.
10. A gas turbine engine turbine assembly in accordance with claim 8 wherein a portion of said n second rows of turbine blades are interdigitated with said at least one low-pressure turbine stator blade row.
11. A gas turbine engine turbine assembly in accordance with claim 8 wherein an amount of total turbine torque that is available from said first rotor shaft is proportional to m/(m+n), and wherein an amount of turbine torque that is available from said second turbine shaft is proportional to n/(m+n).
12. A gas turbine engine turbine assembly in accordance with claim 8 wherein said first compressor comprises a forward fan positioned axially upstream from said second compressor, said second compressor comprises an aft fan positioned axially downstream from said forward fan.
13. A gas turbine engine turbine assembly in accordance with claim 8 wherein one of said first compressor and said second compressor comprises a fan and a booster compressor.
14. A gas turbine engine turbine assembly in accordance with claim 8 wherein a torque demand of said first turbine shaft is different than a torque demand of said second turbine shaft.
15. A gas turbine engine turbine assembly in accordance with claim 8 wherein m and n are selected to generate a turbine torque split that is substantially equal to a ratio of a torque demand of said first turbine shaft and said second turbine shaft.
16. A gas turbine engine assembly comprising a counter-rotatable low pressure turbine comprising:
a low pressure turbine flowpath;
a first forward fan shaft comprising a forward fan coupled to a compressor end of said first forward fan shaft and m first low pressure turbine blade rows extending into said low pressure turbine flowpath; and
a second aft fan shaft coaxially aligned about a longitudinal axis with said first forward fan shaft, said second aft fan shaft including n second low pressure turbine blade rows extending into said low pressure turbine flowpath, wherein m represents the number of first rows of turbine blades, n represents the number of second rows of turbine blades, and m and n are different numbers with respect to each other, wherein at least a portion of said n second low pressure turbine blade rows are interdigitated with at least a portion of said m first low pressure turbine blade rows, and wherein m and n are selected to provide a torque split between the first low pressure turbine shaft and second low pressure turbine shaft of greater than about 1.2:1.
17. A gas turbine engine turbine assembly in accordance with claim 16 wherein m and n are selected to facilitate minimizing a low pressure turbine flowpath tangential momentum differential from a flowpath inlet to a flowpath outlet.
18. A gas turbine engine turbine assembly in accordance with claim 16 wherein said forward fan generates a first torque demand on said first forward fan shaft at an optimal forward fan rotational speed, said aft fan generates a second torque demand on said second aft fan shaft an optimal aft fan rotational speed wherein said first torque demand differs from said second torque demand by an amount greater than twenty percent, said m and said n are selected to facilitate said first low pressure turbine blade rows and said second low pressure turbine blade rows providing said first and said second torque demand.