Mistuned Rotor Blade Recessing for Compressor Flutter Prevention
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Solution Overview
Problem
Compressor rotors in gas turbine engines experience aerodynamic instabilities such as stall flutter and supersonic flutter, leading to potential damage from excessive airfoil stress loads, which existing technologies have not adequately addressed.
Innovation Solution
A method involving a rotor with alternately disposed blades having distinct natural vibration frequencies, where the shape of one blade is modified within a specific zone to increase the frequency difference above a threshold, typically by creating a recessed area on the pressure side radially outward of the mid-span line, to prevent flutter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the natural vibration frequencies of adjacent blades are close to each other, then the rotor structure is simpler and manufacturing is easier, but the rotor becomes susceptible to flutter and aerodynamic instability
Solution Approach 1:
The patent applies local quality by creating a recessed area at a specific location on one blade (radially outwardly of the mid-span line) rather than modifying all blades uniformly. This localized modification changes the natural vibration frequency of that specific blade, creating frequency differentiation between adjacent blades while minimizing overall structural complexity and manufacturing complexity
Solution Approach 2:
The patent introduces asymmetry by modifying only one blade with a recessed area while leaving other blades with the baseline shape. This creates intentional frequency mistuning in the rotor system, where adjacent blades have different natural vibration frequencies, preventing synchronous flutter while maintaining overall rotor balance
2Reliability
If the shape of blades is modified to increase frequency difference, then flutter prevention is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by modifying geometric parameters of a single blade (creating a recessed area with specific depth, width, and radial position) to alter its natural vibration frequency. This controlled parameter modification achieves the desired frequency differentiation while establishing clear manufacturing specifications for the recessed area geometry
3Reliability
If material is removed from the blade to create frequency mistuning, then the frequency difference increases, but the blade strength may be reduced
Solution Approach 1:
The patent applies local quality by removing material only from a specific recessed area on the blade (radially outwardly of the mid-span line) rather than reducing blade thickness throughout. This localized material removal creates frequency mistuning while preserving the overall structural integrity and strength of the blade by maintaining full material sections at critical load-bearing areas
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The modification effectively prevents flutter by ensuring a sufficient frequency difference between adjacent blades, thereby reducing the risk of stress overload and maintaining rotor stability.
Implementation Method 1
natural vibration frequencies of the first blades different from natural vibration frequencies of the second blades
Data Source
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AI summary
A method of manufacturing a mistuned rotor includes: obtaining a rotor 12 having a hub 22 and a plurality of blades 24 protruding from the hub 22, the plurality of blades 24 including first blades 28 and second blades 30 disposed in alternation around a central axis 11 of the rotor 12, natural vibration frequencies of the first blades 28 different from natural vibration frequencies of the second blades 30; determining that a difference between a first natural vibration frequency of a first blade 28 of the first blades and a second natural vibration frequency of a second blade 30 of the second blades is below a threshold L; and modifying a shape of the first blade 28 until the difference between the first natural vibration frequency and the second natural vibration frequency is at or above the threshold L.