Turbine Blade Root Scarf Cuts for Lower Disk Contact Stress
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Solution Overview
Problem
Stress buildup between the attachment roots of turbine rotor blades and the attachment grooves of the disk leads to wear on the disk, reducing the operational life of the disk in gas turbine engines.
Innovation Solution
The turbine blade design incorporates a root section with a fir-tree shaped profile featuring serrations on both the pressure and suction sides, and scarf cuts on the suction side of the root section, which redistribute and reduce contact pressure concentration on the disk, enhancing the operational life of the rotor disk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a traditional attachment root design is used, then the blade can be securely attached to the disk, but stress builds up between the attachment roots and attachment grooves causing wear on the disk
Solution Approach 1:
The patent applies local quality by creating a fir-tree shaped attachment root profile with varying geometry along its length. The root includes a leading end portion and a trailing end portion with different dimensional characteristics, allowing optimized stress distribution at different locations. This non-uniform geometry enables the attachment root to better match the attachment groove profile, reducing stress concentration points while maintaining secure attachment.
Solution Approach 2:
The attachment root is segmented into multiple distinct portions including a leading end portion, a trailing end portion, and intermediate sections. Each segment serves a specific function in stress distribution and attachment security. The root includes multiple contact surfaces that interface with corresponding surfaces in the attachment groove, distributing the attachment forces across multiple discrete contact zones rather than a single continuous interface.
2Ease of manufacture
If the attachment root has a simple geometry, then manufacturing is easier, but stress concentration occurs at contact points reducing disk life
Solution Approach 1:
The patent employs curved and rounded geometries in the attachment root design, particularly at transition zones between different root portions. The root profile includes smooth curved transitions rather than sharp corners, which eliminates stress concentration points. The fir-tree shape incorporates rounded lobes and curved contact surfaces that distribute stress more evenly across the attachment interface, preventing localized pressure peaks while remaining manufacturable using standard machining processes.
3Strength
If the attachment root contacts the disk at concentrated points, then secure attachment is achieved, but wear on the disk increases reducing operational life
Solution Approach 1:
The patent utilizes parameter changes by varying the geometric dimensions, angles, and profiles of the attachment root along its length. The root includes portions with different radial extents, axial lengths, and circumferential angles. Contact surfaces are positioned at specific locations with controlled orientations to optimize the distribution of contact forces. This parametric variation in geometry transforms the contact pattern from concentrated point loads to distributed line and area contacts, reducing wear while maintaining attachment security.
Data Source
AI summary
A turbine blade includes a root section extending from a bottom side of a platform. The root section includes a first end and a second end aft of the first end. A first plurality of serrations is formed on a pressure side of the root section. A second plurality of serrations is formed on a suction side of the root section. Each serration of the second plurality of serrations extends on the suction side from the first end to the second end of the root section. A first scarf cut is formed on each serration of the second plurality of serrations such that each serration of the second plurality of serrations is tapered at the first end of the root section.