Airfoil Root Fillet Compound Curve Machining
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Solution Overview
Problem
Gas turbine engine airfoils face high mechanical stresses at the root junction, which conventional fillet designs struggle to mitigate effectively due to limitations in flow performance and manufacturing constraints, particularly with single-radius fillets.
Innovation Solution
A method using a flank milling cutter with a primary conical milling surface and a secondary tip milling surface defining a compound curve to generate a fillet with varying radii, reducing stress concentration by creating a complex curve geometry at the airfoil-root transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a larger fillet radius is used to reduce stress concentration, then stress concentration is reduced, but flow performance deteriorates and airfoil resonant frequency is affected
Solution Approach 1:
The patent applies different radius values at different locations along the fillet contour. The fillet has a first radius at the airfoil root and a second radius at the gaspath surface, with intermediate radii transitioning between them. This local variation optimizes stress distribution while maintaining flow performance, resolving the contradiction between stress reduction and flow quality.
Solution Approach 2:
The patent changes the geometric parameters of the fillet from a constant radius to a variable radius profile. By defining the fillet contour with multiple radius values that vary along its length, the design achieves both stress concentration reduction and acceptable flow performance through parameter optimization.
2Strength
If a complex compound curve fillet design is implemented to optimize stress distribution, then stress concentration is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent uses a compound curve defined by multiple circular arcs with different radii to create the fillet profile. This curved geometry approach allows the complex stress-distributing shape to be generated through sequential circular interpolations, making the complex design manufacturable through precise but achievable machining operations.
Solution Approach 2:
The fillet contour is segmented into multiple arc segments, each with a specific radius. The first arc has radius R1, the second arc has radius R2, and so on, with each segment transitioning smoothly to the next. This segmentation allows the complex overall shape to be constructed from simpler, manufacturable arc elements.
Data Source
AI summary
An airfoil root fillet having a predetermined compound curve profile can be flank milled with a single flank milling cutter having a generally conical flank milling portion and a rounded tip portion defining a compound curve.