Gas Turbine Fan Blade Axial Lean Flutter Mitigation
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Solution Overview
Problem
Modern gas turbine engine fan blades are susceptible to flutter, especially under conditions of lower specific thrust and higher fan tip loading, which can lead to increased operational challenges and stress due to instability in vibrations.
Innovation Solution
The design of fan blades with a forward axial lean, reduced torsional content in the first natural frequency mode, and specific geometric features such as angles between leading and trailing edges and radial directions to minimize susceptibility to flutter, including aerofoil shapes with forward lean and reduced root and tip portions.
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 parameter changes by modifying the blade geometry parameters, specifically introducing an axial lean angle (beta) between -5° and -0.25° relative to the radial direction. This geometric parameter change alters the blade's aerodynamic characteristics and structural dynamics, reducing torsional content in the first natural frequency mode and thereby decreasing flutter susceptibility while maintaining the efficient operating conditions of lower specific thrust and higher tip loading
2Speed
If fan blades operate at lower rotational speed to reduce specific thrust, then specific thrust is reduced, but flutter margins relative to sea level static working line decrease
Solution Approach 1:
The patent modifies the blade geometry parameters by introducing axial lean, which changes the structural and aerodynamic characteristics of the blade. This parameter change increases the flutter margins at lower rotational speeds by reducing the torsional content in the first natural frequency mode, allowing the engine to operate efficiently at reduced specific thrust while maintaining adequate flutter margins relative to the sea level static working line
3Reliability
If fan blades are designed with forward axial lean to reduce flutter susceptibility, then stability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent implements a controlled parameter change by specifying a limited range for the axial lean angle (beta between -5° and -0.25°). This constrained parameter modification achieves the desired reduction in flutter susceptibility while keeping the geometric deviation from conventional radial blades minimal, thereby limiting the increase in manufacturing complexity to acceptable levels
Solution Approach 2:
The patent introduces asymmetry by leaning the blade axis forward in the axial direction relative to the radial direction. This asymmetric geometry, quantified by the axial lean angle beta, modifies the blade's natural frequency modes to reduce torsional content. The asymmetry is carefully controlled within a small angular range to achieve stability improvement without excessive manufacturing complexity
Data Source
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AI summary
A fan blade for a gas turbine engine is provided with forward axial lean. The fan blade may have a substantially straight leading edge. The geometry of the fan blade results in a lower susceptibility to flutter, thereby allowing a gas turbine engine comprising such a fan blade to operate over a wider range of operating conditions.