Airfoil Rotor Hub Frequency Mistuning for Flutter Reduction
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Solution Overview
Problem
Conventional methods to control rotor instability in gas turbine engines, such as spacing between airfoils or inclusion of cavities, are limited and cannot be applied universally, leading to issues like flutter and high-cycle fatigue in airfoils.
Innovation Solution
Intentionally mistuning airfoils by varying the rotor hub radius to alter the natural frequency of airfoils, reducing coherence between airfoil motion and unsteady pressure fields, thereby eliminating or reducing flutter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods (spacing between airfoils or inclusion of cavities) are used to control rotor instability, then some level of stability control is achieved, but the methods are limited and cannot be applied universally, leading to flutter and high-cycle fatigue
Solution Approach 1:
The patent applies parameter changes by intentionally varying the span of airfoils in a rotor blade, creating spanwise variations that alter the natural frequencies of individual airfoils. This frequency mistuning approach changes the dynamic parameters of the airfoil system to reduce coherence between airfoil motion and unsteady pressure fields, thereby reducing flutter and high-cycle fatigue across different operating conditions and engine types.
2Reliability
If airfoils are intentionally mistuned by varying rotor hub radius to reduce flutter, then propulsive efficiency is enhanced and turbine engine operation in distorted environments is enabled, but the complexity of the rotor hub system increases
Solution Approach 1:
The patent applies local quality by creating intentional variations in airfoil span at specific locations along the rotor hub circumference. Different airfoils are assigned different spans to create local frequency variations, while the overall rotor hub structure maintains its functional integrity. This localized modification approach reduces flutter through frequency mistuning without requiring complete redesign of the entire rotor system.
3Reliability
If the span of airfoils is varied to mistune frequency, then coherence between airfoil motion and unsteady pressure fields is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies dynamics by creating a rotor hub system where airfoil spans are intentionally varied to produce dynamic frequency mistuning effects. The span variations are designed to create beneficial frequency distributions that reduce flutter across different operating conditions. The system accepts certain manufacturing tolerances in achieving precise frequency targets, focusing instead on the overall dynamic behavior and flutter reduction performance.
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 method effectively reduces or eliminates flutter, enhancing propulsive efficiency and enabling turbine engine operation in distorted environments without negatively impacting performance or balance behavior.
Implementation Method 1
intentionally mistune airfoils by varying the rotor hub radius to alter the natural frequency of airfoils, reducing coherence between airfoil motion and unsteady pressure fields, thereby eliminating or reducing flutter
Data Source
AI summary
An airfoil rotor hub system including a rotor hub, the rotor hub having a variable radius around a circumference of the rotor hub, and a plurality of airfoils connected to the rotor hub, a first airfoil in the plurality of airfoils having a first span connected to a surface of the rotor hub at a first radius, and a second airfoil in the plurality of airfoils having a second span connected to the surface of the rotor hub at a second radius. The first radius is different from the second radius, and the first span of the first airfoil is different from the second span of the second airfoil so as to mistune a frequency of the first airfoil and the second airfoil to reduce or substantially to eliminate flutter in the plurality of airfoils.