Variable Pitch Fan Blades for Boundary Layer Ingestion
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Solution Overview
Problem
Conventional aircraft gas turbine engines face inefficiencies due to non-uniform airflow characteristics across different parts of the fan, resulting in suboptimal incidence angles for fan blades and reduced fan efficiency.
Innovation Solution
A fan assembly with a mechanism to adjust the pitch of each fan blade based on its circumferential position, ensuring proper blade pitch alignment with varying airflow velocity vectors, thereby optimizing blade incidence angles and fan efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the fan is mounted adjacent to an aircraft surface, then the engine can be positioned in alternate architectures, but portions of the fan ingest boundary layer airflow with non-uniform velocity, reducing fan efficiency
Solution Approach 1:
The fan blade pitch angles are made variable rather than fixed. Each fan blade can dynamically adjust its pitch angle to optimize performance across different circumferential positions, allowing the fan to adapt to the non-uniform boundary layer airflow while maintaining high efficiency
Solution Approach 2:
Different portions of the fan blade circumference are assigned different pitch angles. The pitch angle varies as a function of circumferential position, with blades at positions experiencing lower velocity boundary layer flow having different pitch angles compared to blades at positions experiencing higher velocity free stream flow, optimizing local performance across the entire fan
2Device complexity
If a single pitch angle is used for all fan blades, then the mechanism is simple, but the blade incidence angles are suboptimal for non-uniform airflow, reducing fan efficiency
Solution Approach 1:
The pitch adjustment mechanism enables dynamic variation of pitch angles for different fan blades based on their circumferential position. This dynamic capability allows the system to optimize blade incidence angles for non-uniform airflow conditions while maintaining a relatively compact and integrated mechanism design
Solution Approach 2:
The pitch angle parameter is varied as a function of circumferential position around the fan. By changing this geometric parameter across different blade positions, the system optimizes the blade incidence angle to match the local airflow velocity, thereby maximizing fan efficiency without requiring overly complex mechanisms
Data Source
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AI summary
A fan assembly (16) for gas turbine engine (18) includes a plurality of fan blades (20) rotatable about a fan rotation axis (A), each of the plurality of fan blades movable about an axis (46) transverse to the fan rotation axis (A), a fan nacelle (26) partially surrounding the plurality of fan blades (20), and a pitch mechanism (40) coupled to the plurality of blades (20) that changes an angle of pitch for each of the plurality of blades corresponding to a circumferential position of the fan blade about the fan rotation axis (A).