Turbine Rotor Dovetail Structure with Variable Spline Curvature
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Solution Overview
Problem
Conventional fir tree structures in turbine blades exhibit non-optimal mechanical interactions and stress concentrations due to simple geometries and uniform curvatures, leading to inefficiencies in stress distribution.
Innovation Solution
A fir tree structure with varying spline profiles is designed, featuring constantly changing radii of curvature that reduce stress concentrations by minimizing peak stresses in high-stress areas and maximizing radii in low-stress areas, optimized through machining processes like EDM or milling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional fir tree structures with simple geometries and uniform curvatures are used, then manufacturing is easier, but stress concentrations occur and mechanical interactions are non-optimal
Solution Approach 1:
The patent applies local quality by varying the spline profile curvatures at different locations along the fir tree structure. Specifically, different radii of curvature are used in different zones (e.g., smaller radii in high-stress areas, larger radii in low-stress areas), allowing each local region to have optimized stress distribution characteristics rather than using a uniform geometry throughout the entire structure.
Solution Approach 2:
The patent implements parameter changes by modifying the geometric parameters of the spline profile, particularly the radii of curvature. The design transitions from uniform curvature parameters to variable curvature parameters, where the radius of curvature changes continuously or in steps along the length of the fir tree structure, thereby optimizing stress distribution while maintaining manufacturability through controlled parameter variations.
2Reliability
If varying spline profiles with constantly changing radii of curvature are used, then stress distribution is optimized, but manufacturing complexity increases
Solution Approach 1:
The patent manages the complexity arising from parameter changes by implementing systematic variations in the spline profile geometry. The radii of curvature are varied according to a defined pattern or function that optimizes stress distribution, and this complexity is balanced against manufacturing capabilities by using profiles that can be produced with modern machining techniques such as CNC milling or EDM.
Solution Approach 2:
The patent addresses structural complexity by applying local quality principles - only specific portions of the fir tree structure have varying curvatures where stress concentrations are expected, while other portions may maintain simpler geometries. This localized application of complex profiles reduces overall structural complexity while still achieving the primary goal of optimizing stress distribution in critical areas.
Data Source
AI summary
A fir tree structure is provided and includes a part extending radially inwardly from a rotating part and having an inward taper. The part has a spline profile forming fixing lobes and necks, which are interleaved with the fixing lobes. The spline profile has constantly changing radii of curvature characterized in that the radii of curvature are relatively reduced in high stress locations and relatively increased in low stress locations.