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, as blades with different natural frequencies experience varying vibration responses to excitation frequencies.
Innovation Solution
The rotor blades are arranged such that each blade has neighboring blades with similar critical natural frequencies, either greater than or less than the median, to minimize the difference in vibration responses and reduce stress, with specific patterns defined by subsets of blades with higher or lower natural frequencies.
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 natural frequencies in specific local patterns around the rotor circumference. Instead of uniform spacing, blades are grouped such that those with similar natural frequencies are positioned adjacently, creating localized zones of frequency similarity that reduce differential vibration amplitudes and stress concentrations at specific locations.
Solution Approach 2:
The patent employs asymmetry by deliberately creating an asymmetric circumferential arrangement of blades based on their natural frequency characteristics. The spacing between blades is intentionally made non-uniform, with closer spacing between blades of similar frequency and larger spacing between blades of dissimilar frequencies, breaking the symmetric pattern to optimize stress distribution.
2Stability of the object's composition
If rotor blades are arranged to balance mass distribution, then rotor balance is improved, but vibration response deteriorates due to uneven natural frequencies
Solution Approach 1:
The patent changes the arrangement parameter from mass-based balancing to natural frequency-based grouping. While mass balance is maintained, the primary organizing principle becomes the natural frequency of each blade, with blades arranged in circumferential sequences that group those with similar frequencies together, thereby optimizing vibration response and reducing differential amplitudes.
3Reliability
If rotor blades are arranged with specific patterns to reduce stress, then reliability is improved, but manufacturing complexity increases due to precise positioning requirements
Solution Approach 1:
The patent applies preliminary action by measuring and determining the natural frequency of each individual blade before assembly, and using this information to pre-determine the optimal circumferential arrangement. This preliminary characterization allows the blades to be positioned correctly from the start, reducing stress and extending life without requiring complex adjustment mechanisms during operation.
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.