Midshaft Rating Design for Low-Pressure Shaft Bending Stability
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Solution Overview
Problem
Next-generation turbomachine engines face challenges in achieving high-speed operation without inducing unstable bending modes and vibrations due to reduced stiffness-to-weight ratios and critical speed limitations of the low-pressure turbine shaft, which affect engine performance and efficiency.
Innovation Solution
Employing various combinations of shaft geometry, material composition, and bearing support configurations, including the use of ceramic matrix composites, to increase the critical speed of the low-pressure turbine shaft while maintaining stability and efficiency, such as through additive manufacturing processes to create integrated components with unique features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the low-pressure turbine shaft operates at high speed, then engine power density and efficiency are improved, but unstable bending modes and vibrations occur due to reduced stiffness-to-weight ratio
Solution Approach 1:
The patent changes the material composition parameter of the shaft from traditional metals to ceramic matrix composites, which fundamentally alters the stiffness-to-weight ratio and enables high-speed operation without inducing unstable bending modes. This material parameter change allows the shaft to operate at higher speeds while maintaining stability.
Solution Approach 2:
The patent employs ceramic matrix composite materials for the low-pressure turbine shaft, combining ceramic fibers in a matrix to achieve superior stiffness-to-weight ratio. This composite material structure provides both the high speed capability and the stability required to avoid critical speed limitations.
2Ease of manufacture
If traditional metal shafts are used, then manufacturing and assembly are simplified, but critical speed limitations prevent high-speed operation
Solution Approach 1:
The patent changes the material parameter from traditional metals to ceramic matrix composites, which fundamentally alters the critical speed characteristics of the shaft. This material parameter change enables the shaft to operate at speeds beyond the limitations of traditional metal shafts.
Solution Approach 2:
The patent applies ceramic matrix composite material specifically to the low-pressure turbine shaft where high-speed operation is required, while other engine components may use traditional materials. This localized application of advanced material optimizes performance where needed without unnecessarily complicating the entire engine system.
3Weight of moving object
If shaft weight is reduced to increase power density, then engine efficiency improves, but stiffness-to-weight ratio decreases causing vibrations
Solution Approach 1:
The patent uses ceramic matrix composite materials for the shaft, which provide superior stiffness-to-weight ratio compared to traditional metals. This composite material allows the shaft to be lighter while simultaneously maintaining or improving vibration stability, resolving the contradiction between weight reduction and stability.
Solution Approach 2:
The patent changes the material composition parameter to ceramic matrix composites, which fundamentally alters the relationship between weight and stiffness. This parameter change enables weight reduction without the penalty of reduced stiffness-to-weight ratio that would occur with traditional materials.
Data Source
AI summary
A turbomachine engine including an engine core including a high-pressure compressor, which has an exit stage having an exit stage diameter (DCORE), a high-pressure turbine, and a combustion chamber in flow communication with the high-pressure compressor and the high-pressure turbine, a power turbine in flow communication with the high-pressure turbine, and a low-pressure shaft coupled to the power turbine and characterized by a midshaft rating (MSR) between two hundred (ft/sec)1/2 and three hundred (ft/sec)1/2. The low-pressure shaft has a redline speed between fifty and two hundred fifty feet per second (ft/sec). The turbomachine engine is configured to operate up to the redline speed without passing through a critical speed associated with a first-order bending mode of the low-pressure shaft. The low-pressure shaft has a length (LMSR) defined by an engine core length (LCORE) given by:LCORE=[m(20+m)*n(10+n)](1100)*DCORE+CIS.