Gas Turbine Rotor Blade Frequency Mistuning
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Solution Overview
Problem
Gas turbine blades are susceptible to destructive vibrations such as flutter and forced response, which can lead to damage and restrict the operable range of turbomachinery, particularly due to identical vibration frequencies and random manufacturing variations.
Innovation Solution
A rotor design for gas turbine engines featuring a central wheel with alternating first and second frequency blades, each with radially inward extending modification slots or voids that differ in size and location to mismatch natural frequency modes, thereby reducing flutter and forced response susceptibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If all blades on a rotor are identical in terms of vibration frequencies, then manufacturing is simplified and cost is reduced, but susceptibility to flutter increases
Solution Approach 1:
The patent applies local quality by introducing frequency-modification slots at specific locations on blade tips rather than uniformly across all blades. Each blade type (first and second frequency blades) has slots positioned at predetermined circumferential locations, creating localized structural variations that alter natural frequencies of specific blades while maintaining overall blade similarity for manufacturing efficiency.
Solution Approach 2:
The patent employs asymmetry by creating two distinct blade types with different frequency characteristics. The first frequency blades and second frequency blades have different slot configurations, resulting in asymmetric frequency distribution around the rotor. This asymmetric mistuning breaks the symmetry of identical blade frequencies, reducing flutter susceptibility while maintaining manufacturing simplicity through standardized blade designs.
2Adaptability or versatility
If random manufacturing variations are present in blades, then manufacturing flexibility is improved, but susceptibility to forced response increases due to peak amplification factors
Solution Approach 1:
The patent applies preliminary action by intentionally designing frequency-modification slots into the blade structure before manufacturing variations occur. The slots are positioned at predetermined circumferential locations with specific dimensions to proactively control natural frequencies, ensuring that even with random manufacturing tolerances, the blades will not experience peak amplification factors that lead to forced response.
Solution Approach 2:
The patent utilizes parameter changes by modifying the natural frequency parameters of specific blades through the frequency-modification slots. By changing the frequency parameters of first and second frequency blades differently, the patent creates a controlled frequency distribution that mitigates the harmful effects of random manufacturing variations, preventing any single blade from experiencing peak amplification.
3Power
If blade vibration amplitude is increased to handle higher aerodynamic loading, then power output is improved, but damage risk from flutter and forced response increases
Solution Approach 1:
The patent converts the potentially harmful effect of high aerodynamic loading into a benefit by using frequency mistuning to reduce flutter and forced response susceptibility. The frequency-modification slots create intentional frequency variations that dissipate vibrational energy, transforming what would be destructive resonance conditions into controlled, lower-amplitude vibrations even under high aerodynamic loading, thereby enabling higher power output with improved blade durability.
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 design reduces the amplitude of vibrations, preventing damage and expanding the operable range by altering aerodynamic damping, allowing for higher aerodynamic loading and improved fuel efficiency through reduced engine weight and avoidance of peak amplification factors.
Implementation Method 1
each of the plurality of second frequency blades is formed to include at least one second-frequency-modification slot, different from the at least one first-frequency-modification slot, that extends inward in the radial direction from a radially-outward tip of the second frequency blade toward the central wheel
Implementation Method 2
The design reduces the amplitude of vibrations, preventing damage and expanding the operable range by altering aerodynamic damping
Implementation Method 3
One type of vibration is known as flutter, which is an aero-elastic instability resulting from the interaction of the flow over the airfoils of the blades and the blades' natural vibration tendencies
Implementation Method 4
Another type of vibration is known as forced response, which is an aero-elastic response to inlet distortion or wakes from upstream airfoils, struts, or any other flow obstruction
Data Source
Figure 1
Figure 2~5
AI summary
A rotor for a gas turbine engine includes a central wheel and a plurality of blades that extend outwardly from the central wheel. The blades are non-uniform to reduce flutter and forced response effects induced during operation of a gas turbine engine including the rotor.