Mistuned Rotor Blade Shaping for Flutter Frequency Separation
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Solution Overview
Problem
Compressor rotors in gas turbine engines experience aerodynamic instabilities such as stall flutter and supersonic flutter, which can lead to undesirable stress loads due to blades vibrating at frequencies close to their natural frequencies.
Innovation Solution
Modify the shape of alternating blades in a rotor by creating a recessed area on one type of blade to increase the difference in natural vibration frequencies between adjacent blades, ensuring they differ by a threshold amount.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If all blades in the rotor have identical shapes, then manufacturing is simplified and cost is reduced, but natural vibration frequencies of adjacent blades become too close, increasing the risk of flutter
Solution Approach 1:
The patent applies local quality by introducing geometric modifications (recesses or material removal) only in specific zones of selected blades, rather than modifying all blades uniformly. This localized modification changes the natural vibration frequencies of specific blades to create sufficient frequency separation, while leaving other blades unchanged, thus maintaining manufacturing simplicity for the majority of blades while achieving flutter protection.
Solution Approach 2:
The patent introduces asymmetry by creating geometric differences between alternating blades (first blades vs. second blades). The modified blades have different shapes from the unmodified blades, creating intentional frequency mistuning. This asymmetric design ensures that adjacent blades have sufficiently different natural vibration frequencies, preventing synchronous vibration and flutter while requiring modifications to only alternating blades.
2Reliability
If the natural vibration frequencies of adjacent blades are made very different, then flutter is prevented, but the rotor becomes more sensitive to unbalance and vibration
Solution Approach 1:
The patent applies partial action by modifying only alternating blades (first blades or second blades) rather than all blades. This creates a balanced mistuning pattern where frequency differences exist between adjacent blades, but the overall rotor maintains symmetry and balance. The partial modification approach prevents flutter while minimizing the introduction of unbalance and excessive vibration.
3Reliability
If blade shapes are modified to achieve frequency separation, then flutter protection is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent minimizes geometric complexity by confining modifications to localized zones on the blade surface, such as recesses or material removal in specific regions. These localized changes achieve the required frequency separation without requiring complex overall blade redesign, thus limiting the increase in manufacturing complexity and cost.
Solution Approach 2:
The patent reduces manufacturing complexity by modifying only alternating blades rather than all blades. This partial modification approach achieves the necessary frequency mistuning for flutter protection while significantly reducing the total number of modified components, tooling requirements, and manufacturing steps compared to modifying every blade.
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
Prevents flutter by ensuring sufficient frequency separation, preventing potential damage from supersonic flutter 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
AI summary
A method includes: obtaining a rotor having a hub and a plurality of blades protruding from the hub, the plurality of blades including first blades and second blades disposed in alternation around a central axis of the rotor, natural vibration frequencies of the first blades different from natural vibration frequencies of the second blades; determining that a difference between a first natural vibration frequency of a first blade of the first blades and a second natural vibration frequency of a second blade of the second blades is below a threshold; and modifying a shape of the first blade until the difference between the first natural vibration frequency and the second natural vibration frequency is at or above the threshold.