Asynchronous Fan Blade Pitching for Gas Turbine Reverse Thrust
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Solution Overview
Problem
Gas turbine engine fan blades with a solidity greater than one often experience blade conflict when rotating into a reverse thrust configuration due to simultaneous flat pitch, which can lead to contact and performance issues, necessitating a solution for asynchronous pitching while maintaining high solidity and ease of assembly.
Innovation Solution
A variable pitch fan system featuring a scheduling ring and linkage arms that allow each fan blade to rotate according to a specific pitch schedule, preventing simultaneous flat pitch rotation and enabling asynchronous blade pitching, thus avoiding contact and enhancing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fan blade solidity is increased to improve fan performance, then fan efficiency is improved, but blade conflict occurs when rotating into reverse thrust configuration
Solution Approach 1:
The patent applies dynamics by making the blade pitch adjustable rather than fixed. The variable pitch mechanism allows blades to change their angle of attack dynamically, enabling them to rotate through flat pitch positions asynchronously. This dynamic adjustment resolves the blade conflict issue while maintaining high solidity for improved fan efficiency.
Solution Approach 2:
The patent segments the blade pitch control into individual independent controls for each blade. By dividing the pitch control system so that each blade can be pitched independently through different scheduling slots, the system prevents simultaneous flat pitch rotation that causes blade contact, while maintaining high solidity configuration.
2Adaptability or versatility
If variable pitch mechanism is added to enable reverse thrust, then reverse thrust capability is achieved, but blade contact occurs during pitch rotation
Solution Approach 1:
The variable pitch mechanism enables dynamic adjustment of blade angles, allowing the fan to achieve reverse thrust capability. The dynamic pitch control system rotates blades through flat pitch positions at different times using asynchronous scheduling, preventing blade contact while enabling full reverse thrust operation.
Solution Approach 2:
The patent employs periodic action through scheduled pitch rotation sequences. Different blades follow different pitch schedules with staggered timing, creating a periodic pattern where blades rotate through flat pitch at intervals rather than simultaneously. This periodic staggering prevents blade contact while maintaining reverse thrust capability.
3Reliability
If asynchronous pitching is implemented to prevent blade contact, then blade conflict is avoided, but mechanism complexity increases
Solution Approach 1:
The pitch control mechanism is segmented into modular components with individual pitch controls for each blade. This segmentation allows independent pitch scheduling while maintaining a relatively simple overall structure. Each blade has its own pitch control linkage connected to scheduling slots, avoiding the need for complex centralized control systems.
Solution Approach 2:
The patent introduces an intermediary scheduling ring mechanism that coordinates blade pitch timing. This scheduling ring with indexed slots acts as a mediator between the pitch control system and individual blades, providing simple mechanical indexing that achieves asynchronous pitching without requiring complex electronic control or sophisticated mechanism design.
Data Source
AI summary
An actuation assembly for a variable pitch fan for a gas turbine engine is provided. The actuation assembly generally includes a plurality of fan blades, a scheduling ring, and a plurality of linkage arms. The plurality of fan blades are rotatably coupled to a disk and extend radially therefrom. The scheduling ring is rotatable relative to the disk and has a plurality of slots. Each of the plurality of linkage arms are operatively coupled to one of the plurality of fan blades and to one of the plurality of slots. Each of the plurality of fan blades rotate according to a blade pitch schedule defined by the slot to which it is operatively coupled, and at least two of the plurality of slots define different blade pitch schedules.