Segmented Stack Nut for Gas Turbine Thermal Expansion
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Solution Overview
Problem
In gas turbine engines, thermal gradients cause non-uniform thermal expansion of stack nuts, leading to uneven clamping forces that can warp rotors and disrupt sealing contacts, resulting in fluid leakage, reduced efficiency, and increased wear and component failure.
Innovation Solution
The shaft assembly incorporates a stack nut design with segmented components that maintain a uniform axial clamp force through controlled thermal expansion, featuring a clamping nut segment, torquing nut segment, and seal land nut segment, which are configured to minimize disruptive effects from thermal gradients by maintaining a perpendicular orientation and using anti-rotation and damping elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a traditional solid stack nut is used, then the structure is simple, but thermal gradients cause non-uniform expansion and warping leading to non-uniform clamping force
Solution Approach 1:
The stack nut is divided into multiple independent segments that can expand and contract independently in response to thermal gradients. Each segment is separated by expansion gaps, allowing differential thermal expansion without causing warping or non-uniform clamping force. This segmentation resolves the contradiction by maintaining structural simplicity while improving reliability through controlled thermal behavior.
Solution Approach 2:
Different regions of the stack nut are given different properties through the segmentation design. The expansion gaps are strategically placed to allow specific local areas to expand more than others, accommodating thermal gradients while maintaining overall clamping force uniformity. This local quality approach allows the structure to adapt to thermal conditions without becoming overly complex.
2Reliability
If the stack nut is made thicker to reduce thermal gradient effects, then thermal expansion uniformity improves, but the device complexity and weight increase
Solution Approach 1:
Rather than increasing thickness, the patent segments the stack nut into multiple thinner sections with expansion gaps. This approach achieves thermal expansion uniformity by allowing each segment to expand independently, avoiding the need for increased overall thickness and the associated complexity and weight penalties.
3Device complexity
If conventional sealing methods are used, then the sealing structure is simple, but fluid leakage occurs due to rotor warping from non-uniform clamping force
Solution Approach 1:
The sealing structure is segmented into multiple independent sealing segments that can accommodate rotor warping and movement. Each segment maintains contact with the rotor surface independently, ensuring continuous sealing effectiveness even when the rotor warps due to thermal effects, without requiring a complex single-piece sealing design.
4Reliability
If the stack nut is designed to accommodate thermal expansion, then clamping force uniformity improves, but manufacturing complexity increases
Solution Approach 1:
The stack nut is manufactured as separate segments that are assembled together with expansion gaps. This segmentation approach actually simplifies manufacturing compared to creating a monolithic structure with built-in expansion compensation features. Each segment can be manufactured independently using standard processes, and the assembly is straightforward, maintaining ease of manufacture while achieving clamping force uniformity.
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 ensures a consistent seal between rotor and stator contact surfaces, reducing fluid leakage, enhancing engine efficiency, and minimizing wear and component failure risks by maintaining a uniform clamping force despite thermal expansion.
Implementation Method 1
During operation, the stack nut may be subject to a thermal gradient. The thermal gradient may cause different regions of the stack nut to thermally expand at different rates and warp.
Implementation Method 2
using anti-rotation and damping elements
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A shaft assembly for a gas turbine engine that includes a shaft (12) with a threaded shaft segment (32), an annular rotor (14) disposed on the shaft (12), and annular stack nut (24). The stack nut (24) includes a base nut segment (54) and a clamping nut segment (56). The base nut segment (54) includes a threaded nut bore (62) that is mated with the threaded shaft segment (32). The clamping nut segment (56) axially extends from the base nut segment (54) to a load bearing surface (70). The clamping nut segment (56) includes a radial thickness that decreases as the clamping nut segment (56) extends from the load bearing surface (70) towards the base nut segment (54). The load bearing surface (70) exerts a force against the rotor (14), securing the rotor (14) to the shaft (12).