Dual-Fan Geared Architecture for Counter-Rotating Turbine Airflow
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Solution Overview
Problem
Recent gas turbine engine architectures with geared connections between the fan and turbine sections face challenges in optimizing performance due to differing rotational directions and speeds between the fan and low-pressure compressor, which affect efficiency and noise levels.
Innovation Solution
The integration of a cylindrical static structure that combines a planet gear system and a star gear system, with equal sun gear teeth and specific reduction ratios, supports both fan assemblies and imparts counteracting swirls to airflow, reducing the need for additional structural support and optimizing power transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a geared architecture is used to connect the fan section and turbine section with different rotational speeds and directions, then engine performance is maximized, but the device complexity increases
Solution Approach 1:
The patent combines a planet gear system and a star gear system into a single integrated geared architecture. The planet gear system connects the fan shaft to the low-pressure compressor shaft, while the star gear system connects the fan shaft to the high-pressure compressor shaft. These two gear systems are merged through shared components (the fan shaft and engine static structure), allowing differential speed and direction control for multiple compressor stages while maintaining a compact, unified structure that maximizes engine performance without excessive complexity.
Solution Approach 2:
The fan shaft serves multiple functions: it drives the fan blades directly, connects to the planet gear system to drive the low-pressure compressor, and connects to the star gear system to drive the high-pressure compressor. This multi-functional design allows a single rotating component to control multiple compression stages at different speeds and directions, reducing the overall number of independent drive systems needed while maintaining optimized performance across all components.
2Productivity
If the fan rotates in a first direction at a first speed and the low pressure compressor rotates in the opposite direction at a higher speed, then engine performance is maximized, but noise levels increase
Solution Approach 1:
The patent segments the compression function into two separate systems: a low-pressure compressor driven by the planet gear system and a high-pressure compressor driven by the star gear system. Each compressor operates at optimized speed and direction for its specific function, with the low-pressure compressor rotating opposite to the fan to reduce noise, while the high-pressure compressor can rotate in the same direction. This segmentation allows noise control at the low-pressure stage without compromising overall engine performance.
3Productivity
If separate rotors are used for the fan and compressors, then performance optimization is achieved, but the quantity of parts increases
Solution Approach 1:
The patent merges the drive systems for the low-pressure and high-pressure compressors into a unified geared architecture centered on the fan shaft. Rather than using completely separate motors or drive mechanisms for each compressor, both compressors are driven through gear systems that share the fan shaft and engine static structure as common elements. This reduces the total quantity of independent parts while maintaining the performance benefits of differential rotation.
Data Source
Figure 1
Figure 2
AI summary
A gear system (48) for a gas turbine engine (20) includes a planet gear system (60) which includes an output (84) attached to a carrier (86) for rotating a first fan assembly (42A) in a first direction. A star gear system (62) includes an output (68) attached to a ring gear (74) for rotating a second fan assembly (42B) in a second direction. A sun gear (64) of the star gear system (62) is mechanically attached to a sun gear (80) of the planet gear system (60).