Gas Turbine Rotor Blade Arrangement for Stress Reduction
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Solution Overview
Problem
Conventional arrangements of rotor blades in gas turbine engines can lead to uneven natural frequencies among blades, resulting in high stress and potential premature failure due to differential vibration amplitudes, despite providing adequate dynamic balancing.
Innovation Solution
The rotor blades are arranged such that each blade has neighboring blades with similar critical mode stiffness, either greater than or less than the median, to minimize the difference in natural frequencies and reduce stress, with specific patterns defined by subsets R and S of blades with higher or lower critical mode stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If rotor blades are arranged with equal circumferential spacing to simplify assembly, then ease of operation is improved, but stress distribution deteriorates due to mismatched natural frequencies
Solution Approach 1:
The patent applies local quality by arranging blades with different critical mode stiffness values in specific circumferential positions rather than using uniform spacing. Blades are grouped into sets based on their stiffness characteristics and placed in predetermined patterns that ensure adjacent blades have similar natural frequencies, thereby optimizing stress distribution while maintaining manufacturing simplicity
Solution Approach 2:
The invention changes the arrangement parameter from equal circumferential spacing to a pattern based on critical mode stiffness values. By varying the circumferential positions according to blade stiffness parameters, the patent achieves synchronized vibration responses and reduced stress concentrations without compromising assembly ease
2Stability of the object's composition
If rotor blades are arranged to balance mass differences, then rotor balance is improved, but vibration stress worsens due to uneven natural frequencies
Solution Approach 1:
The patent addresses vibration stress by implementing local quality in the circumferential arrangement - blades with similar critical mode stiffness values are positioned adjacent to each other, creating localized zones of synchronized vibration characteristics. This prevents the harmful effect of differential vibration amplitudes between adjacent blades while maintaining overall rotor balance
Solution Approach 2:
Instead of arranging blades by mass alone (conventional approach), the patent inverts the arrangement criterion to prioritize critical mode stiffness values. This inversion resolves the contradiction by ensuring that blades with similar stiffness are adjacent, thereby synchronizing natural frequencies and reducing vibration stress while still achieving acceptable rotor balance
3Ease of manufacture
If rotor blades are arranged in conventional patterns, then manufacturing simplicity is maintained, but blade life deteriorates due to high stress from frequency mismatch
Solution Approach 1:
The patent applies preliminary action by pre-categorizing blades into sets based on their critical mode stiffness values before assembly. This preliminary classification enables the implementation of optimized circumferential arrangements that extend blade life, while the standardized grouping process maintains manufacturing simplicity and does not significantly complicate the production workflow
Data Source
AI summary
The blades for a rotor of a gas turbine engine are all manufactured to the same design. However, manufacturing tolerances mean that in practice each individual blade is different to the others. It is proposed to arrange the blades around the circumference of the rotor in a manner that limits excessive stress being induced in the blades due to differences in the vibration response between a given blade and its two neighbouring blades.