Arced Arc Segment Seal Slots for Reduced Gas Leakage
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Solution Overview
Problem
Gas turbine engines face challenges in maintaining effective seals between arc segments to prevent gas leakage, particularly due to the rough surfaces left by electromagnetic discharge machining (EDM) and the need for welding open slots produced by grinding, which can compromise sealing performance.
Innovation Solution
The use of arc segments with complementary concave and convex arced slot portions and a feather seal with convex edges, which are symmetric and exclude straight edges, to create a labyrinth seal by entrapment, enhancing sealing efficiency and manufacturing ease through grinding without sweeping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electromagnetic discharge machining (EDM) is used to machine arc segments, then manufacturing capability is improved, but surface roughness increases and sealing performance deteriorates
Solution Approach 1:
The seal slot is divided into multiple portions (first slot portion with concave arced back wall, second slot portion with convex arced edge) that can be machined by different processes. This segmentation allows EDM to be used for the concave back wall where roughness is acceptable, while the convex edge is machined by grinding for smooth surface finish, thus resolving the contradiction between manufacturing capability and surface precision.
Solution Approach 2:
Different surface quality requirements are applied to different portions of the seal slot. The concave arced back wall can have rougher surface from EDM, while the convex arced edge requires smooth surface from grinding. This local differentiation of quality requirements allows each portion to be optimized for its specific function, resolving the contradiction between ease of manufacture and manufacturing precision.
2Manufacturing precision
If grinding is used to machine slot portions, then surface finish is improved, but welding is required to close open slots which increases complexity
Solution Approach 1:
Instead of machining the entire slot open and then welding it closed, the slot is designed with a convex arced edge portion that is ground smooth to provide sealing surface, while the concave back wall portion is machined by EDM. The convex edge naturally closes the slot opening without requiring welding, inverting the conventional approach and eliminating the welding step while maintaining good surface finish where needed.
3Ease of manufacture
If straight edges are used in feather seal, then manufacturing is simplified, but sealing performance deteriorates due to gas leakage
Solution Approach 1:
The feather seal is designed with entirely curved surfaces including convex arced edges instead of straight edges. The curved geometry conforms to the arc segments and provides continuous contact for sealing, preventing gas leakage. While curved surfaces are slightly more complex to manufacture than straight edges, the curvature is essential for achieving reliable sealing in the radial arrangement of arc segments.
Data Source
AI summary
A gas turbine engine includes first and second arc segments that each have leading and trailing sides and first and second circumferential sides. The first circumferential side includes a first slot portion and the second circumferential side includes a second slot portion. The first and second slot portions are in registration and together define a seal slot. At least the first slot portion has a first concave arced back wall. A feather seal is entrapped in the seal slot and includes first and second feather seal circumferential sides. At least the first feather seal circumferential side has a first convex arced edge that is adjacent the first concave arced back wall of the first slot portion.