Gas Turbine Strut Cover Variable Thickness Design
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Solution Overview
Problem
The existing strut covers for gas turbines experience high cycle fatigue due to stress generated by vibration and heat from combustion gases, leading to potential breakage or damage, especially as output power and gas temperatures increase.
Innovation Solution
A strut cover design featuring a cylindrical sheet metal member with a flare member that has a thicker curved portion, reducing stress concentration and thermal stress, and is connected to both the outer and inner diffusers to enhance high cycle fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the strut cover has a uniform thickness from outer end to inner end, then the manufacturing is simple, but the stress is concentrated on the flare portion causing breakage or damage due to high cycle fatigue
Solution Approach 1:
The strut cover transitions from uniform thickness to variable thickness, with the flare portion having increased thickness compared to the cylindrical portion. This local quality change concentrates material where stress is highest (the flare portion) while maintaining thinner sections where stress is lower, thereby resolving the stress concentration problem without excessive material usage throughout the entire component.
Solution Approach 2:
The thickness parameter of the strut cover is changed from a constant value to a variable value that depends on the location. Specifically, the flare portion has a greater thickness than the cylindrical portion, creating a gradient in the thickness parameter that corresponds to the gradient in stress distribution, thus improving high cycle fatigue strength at the critical flare region.
2Power
If the output power of the gas turbine is increased, then the power generation capability is improved, but the temperature of the combustion gas increases causing the strut cover to become hot and increasing the risk of break or damage
Solution Approach 1:
The increased thickness at the flare portion provides additional material volume that can absorb and dissipate thermal energy, creating a local thermal mass effect. This local quality enhancement at the stress-concentration zone also happens to be the zone most exposed to thermal stress, providing dual benefits of mechanical and thermal resilience.
3Strength
If the flare member has a larger thickness, then the stress concentration is reduced improving fatigue strength, but the flow passage cross-sectional area may be reduced
Solution Approach 1:
The thickness increase is applied locally only to the flare portion where stress concentration occurs, while the cylindrical portion maintains its original thickness. This localized approach ensures that the flow passage area is preserved in the cylindrical section while gaining structural strength at the critical flare transition zone.
Data Source
AI summary
A strut cover for a gas turbine includes: a cylindrical sheet metal member having a hollow portion; and a flare member that is connected to one end of the cylindrical sheet metal member in an axial direction of the cylindrical sheet metal member and includes a curved portion having an outer surface such that a distance from a center axis of the cylindrical sheet metal member to the outer surface increases with increasing a distance from the cylindrical sheet metal member in the axial direction. The flare member has a thickness larger than a minimum thickness of the cylindrical sheet metal member at least in the curved portion.