Geared Low-Pressure Turbine Layout for Fan Speed Decoupling
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Solution Overview
Problem
There is an ongoing need for improved engine configurations for geared turbofan engines to enhance efficiency and performance, particularly in turbomachinery engines with complex design challenges and interdependent components.
Innovation Solution
The development of turbomachinery engines with a gearbox configuration that couples a low-pressure turbine to the bypass fan, allowing for different rotational speeds through gear assemblies such as epicyclic and non-epicyclic gearboxes, which improve efficiency and performance by optimizing the gear ratio and reducing installed drag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a direct drive configuration is used where the power turbine is directly coupled to the bypass fan, then the engine structure is simpler, but the power turbine and bypass fan must rotate at the same speed which reduces efficiency and performance
Solution Approach 1:
A gearbox is introduced as an intermediary component between the power turbine and the bypass fan. This gearbox includes a first gear set with a first gear ratio that couples the power turbine to an intermediate shaft, and a second gear set with a second gear ratio that couples the intermediate shaft to the bypass fan. This multi-stage gear transmission system allows the power turbine and bypass fan to rotate at different optimal speeds while maintaining a manageable overall gear ratio, thereby resolving the contradiction between structural simplicity and operational efficiency.
2Device complexity
If a single-stage gearbox is used to couple the power turbine to the bypass fan, then the device complexity is reduced, but the gear ratio requirements become more difficult to meet for optimized efficiency
Solution Approach 1:
The single-stage gearbox is segmented into multiple independent gear sets arranged in series. The first gear set provides a first gear ratio between the power turbine and an intermediate shaft, while the second gear set provides a second gear ratio between the intermediate shaft and the bypass fan. This segmentation allows each gear set to be optimized independently for specific ratio requirements, making it easier to achieve overall gear ratio optimization while keeping individual gear sets manageable in complexity.
3Device complexity
If the power turbine and bypass fan rotate at the same speed, then the engine configuration is simpler, but the specific fuel consumption and operational capability at high altitudes and speeds are limited
Solution Approach 1:
The engine configuration transitions from a static direct-drive coupling to a dynamic gear-transmitted coupling that allows independent rotational speeds. The gearbox enables the power turbine to rotate at a higher speed optimized for power generation while the bypass fan rotates at a lower speed optimized for thrust generation. This dynamic speed differentiation improves specific fuel consumption and operational capability at high altitudes and speeds while maintaining acceptable structural complexity through the use of epicyclic and non-epicyclic gear mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The gearbox configuration enables improved efficiency and performance by allowing the power turbine and bypass fan to operate at respective rotational speeds, enhancing specific fuel consumption and enabling operation at higher cruise altitudes and speeds.
Implementation Method 1
a gearbox configured to couple the low-pressure turbine to the bypass fan, wherein the gearbox comprises a first gear set configured to couple the low-pressure turbine to an intermediate shaft of the gearbox with a first gear ratio and a second gear set configured to couple the intermediate shaft to the bypass fan with a second gear ratio
Data Source
AI summary
A turbomachinery engine includes a fan assembly, a low-pressure turbine, and a gearbox. The fan assembly includes a plurality of fan blades. The low-pressure turbine includes four rotating stages. The low-pressure turbine includes an area ratio equal to the annular exit area of an aft-most rotating stage of the low-pressure turbine divided by the annular exit area of a forward-most rotating stage of the low-pressure turbine. In some instances, the area ratio is within a range of 2.0-5.1. Additionally (or alternatively) the low-pressure turbine includes an area-EGT ratio within a range of 1.05-1.6.