High-Pressure Shaft Rating for Turbine Bending Stability
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Solution Overview
Problem
Turbine engines with higher bypass ratios face instability due to reduced stiffness-to-weight ratio and increased excitation of bending modes, particularly the Alford and third modes, leading to vibrations and reduced efficiency.
Innovation Solution
Optimized shaft designs and materials, including ceramic matrix composites, with specific geometries and dimensions to enhance stability and efficiency, such as CMC materials for high-pressure turbine modules, and integrated bearing support systems to manage dynamic excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If higher bypass ratio is used to improve fuel efficiency and reduce emissions, then engine efficiency improves, but shaft stability deteriorates due to reduced stiffness-to-weight ratio and increased bending mode excitation
Solution Approach 1:
The patent changes the material parameters of the shaft from traditional metals to ceramic matrix composites (CMC), fundamentally altering the stiffness-to-weight ratio. This material substitution enables the shaft to maintain higher stability while supporting the higher bypass ratio configuration, thus resolving the contradiction between fuel efficiency and shaft stability
Solution Approach 2:
The patent employs ceramic matrix composite materials for the high-pressure shaft, combining ceramic fibers with a matrix material to create a composite structure. This composite approach provides both the lightweight properties needed for high bypass ratio efficiency and the enhanced stiffness required to mitigate bending mode excitation and maintain shaft stability
2Power
If shaft weight is reduced to improve power-to-weight ratio, then engine power density improves, but shaft stability deteriorates due to reduced stiffness-to-weight ratio
Solution Approach 1:
The CMC composite material provides a superior strength-to-weight ratio compared to traditional metallic shafts. The composite structure maintains adequate weight for high power density while the ceramic fiber reinforcement provides enhanced stiffness to prevent bending mode excitation, simultaneously achieving both power density and stability goals
Solution Approach 2:
The patent applies CMC material specifically to the high-pressure shaft where both weight reduction and stability are critical. The local substitution of material in this high-stress component optimizes the power-to-weight ratio while maintaining sufficient stiffness through the composite's inherent properties
3Speed
If redline speed is increased to improve engine performance, then power output improves, but shaft instability increases due to excited bending modes
Solution Approach 1:
The patent changes the critical speed parameters of the shaft through material substitution. The CMC material alters the shaft's natural frequencies and damping characteristics, allowing the redline speed to be increased while avoiding resonance with excited bending modes, thus maintaining stability at higher speeds
Solution Approach 2:
The patent considers the dynamic behavior of the shaft at varying speeds, using CMC material properties to optimize the shaft's response to rotational speeds. The material's damping characteristics and stiffness properties help suppress bending mode excitation across the operating range, enabling higher redline speeds with maintained stability
Data Source
AI summary
A turbomachine engine includes an engine core including a high-pressure compressor, a high-pressure turbine, and a combustion chamber in flow communication with the high-pressure compressor and the high-pressure turbine. The engine core has a length (LCORE), and the high-pressure compressor has an exit stage diameter (DCORE). A high-pressure shaft is coupled to the high-pressure compressor and the high-pressure turbine. The high-pressure shaft is characterized by a high-speed shaft rating (HSR) from 1.5 to 6.2, and a ratio of LCORE/DCORE is from 2.1 to 4.3.