Stiffened Rotor Shaft Structure for Low-Weight Bending Rigidity
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Solution Overview
Problem
Gas turbine engine shafts face the challenge of meeting conflicting requirements of stiffness and low weight, particularly in the high pressure compressor and low pressure turbine sections.
Innovation Solution
The implementation of internal stiffening ribs with a stiffened wall thickness ratio between 1.125 and 2.1, located axially proximate specific stages of the high pressure compressor, provides increased bending stiffness while minimizing weight and shaft deflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the shaft wall thickness is increased to improve stiffness, then the bending stiffness increases, but the weight increases
Solution Approach 1:
The patent applies local quality by positioning stiffening ribs at specific locations along the shaft where bending moments are highest (proximate to compressor stages 2, 7, and 8). This localized reinforcement provides the necessary stiffness only where needed, rather than uniformly thickening the entire shaft, thereby minimizing weight while achieving the required bending stiffness performance.
2Stability of the object's composition
If the shaft wall thickness is increased to reduce deflection, then the mid-shaft torque tube deflection decreases, but the weight increases
Solution Approach 1:
The stiffening ribs are strategically positioned at locations experiencing maximum deflection under operational loads. By concentrating material only at these critical locations rather than uniformly throughout the shaft, the design achieves reduced mid-shaft deflection while minimizing overall weight increase.
3Strength
If stiffening ribs are added to the shaft, then the bending stiffness increases, but the device complexity increases
Solution Approach 1:
The shaft is segmented into regions with different structural characteristics - sections with stiffening ribs and sections without. This segmentation allows the design to achieve enhanced bending stiffness only where required by operational demands, while maintaining simpler construction in other areas, thereby limiting the overall increase in device complexity.
4Weight of moving object
If the stiffened wall thickness ratio is optimized between 1.125-2.1, then the weight is reduced by approximately 10%, but the manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the stiffened wall thickness ratio within a specific range (1.125-2.1) to achieve the best compromise between weight reduction and manufacturing feasibility. This parameter optimization allows for approximately 10% weight reduction while keeping manufacturing precision requirements at achievable levels through careful selection of the thickness ratio within this range.
Data Source
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AI summary
A shaft (40) for a gas turbine engine (20) includes an inner contour (76) with a stiffening rib (80, 80A, 80B) that defines a stiffened wall thickness (82) related to a nominal wall thickness (84) according to a ratio between about 1.125 - 2.1.