Conical Flange Bolted Joint for Gas Turbine Rotor
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Solution Overview
Problem
Conventional bolted joints in gas turbine engines face challenges with Low Cycle Fatigue (LCF) due to interruptions in the rotor structure and High Cycle Fatigue (HCF) caused by thermal gradients and gravity-induced sag, leading to potential flange heel opening and increased stress on bolts.
Innovation Solution
A conical flange bolted joint design where the flange surfaces and spacers are angled, preventing bolts from passing through the rotor structure and maintaining a closed heel interface to reduce HCF stress, while allowing a gap at the toe to accommodate thermal expansion and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If through-bolted design is used, then structural strength is improved, but Low Cycle Fatigue life deteriorates due to holes interrupting the rotor structure
Solution Approach 1:
The rotor assembly is segmented into multiple components (rotor wheel, spacer, flanges) connected by bolts, allowing the main rotor structure to remain intact without through-holes while still achieving structural strength through the segmented bolted connection
2Reliability
If flange-bolted design is used, then Low Cycle Fatigue life is improved by avoiding holes in the rotor structure, but High Cycle Fatigue stress increases due to flange heel opening
Solution Approach 1:
The flange interface is designed with asymmetric contact where the heel end is constrained to remain closed while the toe end allows separation, creating an asymmetric load path that prevents HCF stress concentration at the heel while maintaining LCF reliability
Solution Approach 2:
Different regions of the flange interface have different functional properties: the heel region is designed to remain closed and constrained to prevent HCF stress, while the toe region is designed to allow opening and closing to accommodate thermal expansion and contraction
3Manufacturing precision
If conventional flange design with rabbet interference is used, then alignment is improved, but High Cycle Fatigue stress increases due to prying at the flange heel
Solution Approach 1:
The rabbet interference feature is removed from the design, replacing it with a conical flange interface that achieves alignment through geometric constraint rather than interference fit, eliminating the prying action that causes HCF stress
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances the durability of bolted joints by minimizing LCF and HCF stress, ensuring the flange heel remains closed and reducing the risk of bolt failure due to gravity sag and thermal expansion, thereby extending the lifespan of gas turbine components.
Implementation Method 1
Either each flange surface or a surface of the spacer is conical, i.e., non-perpendicular to a centerline of the gas turbine, such that in an unconstrained state, e.g., with a bolt untightened, a heel end of each flange surface is closer to the spacer than a toe end of each flange surface
Implementation Method 2
allowing a gap at the toe to accommodate thermal expansion and contraction
Implementation Method 3
The gas turbine rotor is very heavy and gravity causes the rotor to sag under its own weight, subjecting the bolted joints to high cycle fatigue (HCF)
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A bolted flange assembly (100) for securing rotating components in a gas turbine. The bolted flange assembly (100) includes two rotating wheels (102), each wheel (102) having at least one arm (106) extending towards a spacer (104) positioned partially between the two rotating wheels (102), wherein each arm (106) has a flange surface (108) facing the spacer (104). Either each flange surface (108) or a surface of the spacer (104) is conical, i.e., non-perpendicular to a centerline of the gas turbine, such that in an unconstrained state, a heel end (110) of each flange surface (108) is closer to the spacer (104) than a toe end (112) of each flange surface (108); and a bolt (114) extending through the arm (106) of each rotating wheel (102) and the spacer (104).