Gas Turbine Fan Blade Thickness Distribution for Flutter Reduction
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Solution Overview
Problem
Modern gas turbine engines are more susceptible to fan blade flutter due to lower specific thrust and higher fan tip loading, which can lead to increased stress and operability challenges, especially at certain rotational speeds and thrust conditions.
Innovation Solution
The design of fan blades with a specific thickness distribution, where the position of maximum thickness along the camber line varies across the blade span, increasing thickness in certain regions to elevate the first modal frequency and reduce torsion, thereby reducing the susceptibility to flutter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If fan blades are designed with lower specific thrust and higher fan tip loading to improve efficiency, then energy efficiency is improved, but susceptibility to flutter increases
Solution Approach 1:
The patent applies local quality by varying the thickness distribution of the fan blade along its span. Specifically, the blade thickness is increased in the inner region (between 20-40% of blade span from root) while maintaining or reducing thickness in other regions. This localized modification of blade geometry provides targeted stiffening to reduce flutter susceptibility in the critical inner blade region without compromising overall blade efficiency or increasing weight uniformly across the entire blade.
Solution Approach 2:
The patent employs parameter changes by modifying the thickness distribution parameter along the blade span. The thickness-to-chord ratio is specifically adjusted in different radial regions, with the inner region (20-40% span) having increased thickness compared to conventional designs. This parameter modification changes the natural frequencies and mode shapes of the blade, thereby reducing flutter susceptibility while maintaining the efficiency benefits of lower specific thrust and higher tip loading.
2Reliability
If fan blade thickness is increased to reduce flutter susceptibility, then reliability is improved, but blade weight increases
Solution Approach 1:
The patent applies local quality by concentrating the thickness increase specifically in the inner blade region (20-40% of blade span from root) rather than uniformly increasing thickness across the entire blade. This localized approach provides the necessary stiffening to reduce flutter susceptibility in the critical inner region where flutter modes typically originate, while minimizing the overall weight penalty by avoiding unnecessary material in other blade regions.
3Use of energy by moving object
If fan blades operate at lower rotational speeds to improve efficiency, then energy efficiency is improved, but stall and flutter margins are reduced
Solution Approach 1:
The patent employs parameter changes by modifying the thickness distribution parameter along the blade span, specifically increasing thickness in the inner region (20-40% span). This parameter modification elevates the natural frequencies of the blade, particularly the first modal frequency, which directly improves flutter margins. The changed geometric parameters alter the blade's dynamic characteristics, allowing for safer operation at lower rotational speeds where efficiency is improved.
Data Source
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AI summary
A fan blade is provided with an aerofoil portion for which, at radii between 20% and 40% of the blade span, the location of the position of maximum thickness along the camber line is at less than a defined percentage of the total length of the camber line. For all cross-sections through the aerofoil portion at radii greater than 70% of the blade span, the location of the position of maximum thickness along the camber line is at more than a defined percentage of the total length of the camber line. The geometry of the fan blade may result in a lower susceptibility to flutter.