Turbine Blade Lateral Offset for Centrifugal Balance
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Solution Overview
Problem
The existing method of aligning the centers of mass of turbine blade airfoil, platform, and root along a stacking axis leads to increased mechanical stress and leakage of combustion gas due to the proximity of the leading and trailing edges to the platform, causing stress concentrations and potential gas leakage.
Innovation Solution
The airfoil and platform are laterally offset to balance centrifugal forces about the attachment plane, allowing the common center of mass to be located on or within the attachment plane, thereby redistributing stress and reducing leakage by using equations to calculate optimal offsets for static and dynamic balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the centers of mass of the airfoil, platform, and root are aligned along a stacking axis, then the centrifugal loads are distributed evenly on the root, but the leading and trailing edges of the airfoil are positioned close to the platform, causing stress concentrations and potential combustion gas leakage
Solution Approach 1:
The patent applies asymmetry by laterally offsetting the airfoil from the platform in the radial direction. The airfoil center of mass is positioned at a first radial distance from the disc center, while the platform center of mass is positioned at a second radial distance, creating an asymmetric configuration that separates the airfoil leading/trailing edges from the platform edges, thereby reducing stress concentrations and preventing combustion gas leakage while maintaining balanced centrifugal loads through calculated offset distances
2Volume of moving object
If the airfoil leading and trailing edges are positioned close to the platform, then the structure is compact, but stress concentrations occur and combustion gas leakage increases
Solution Approach 1:
The patent uses the counterweight principle by positioning the airfoil and platform centers of mass at different radial distances to create balanced centrifugal forces. This calculated offset configuration acts as a counterbalancing mechanism that maintains structural integrity and prevents combustion gas leakage by ensuring that the airfoil edges do not contact or closely approach the platform edges during rotation, while still achieving a compact overall design
3Reliability
If the centers of mass are aligned for even load distribution, then root stability is improved, but the design life is reduced due to stress concentrations
Solution Approach 1:
The patent resolves this contradiction by implementing asymmetric radial positioning of the airfoil and platform. The airfoil is offset radially from the platform such that their centers of mass are at different distances from the disc center. This asymmetric configuration maintains even distribution of centrifugal loads on the root (improving reliability) while simultaneously separating the airfoil leading/trailing edges from the platform edges, eliminating stress concentrations that would reduce design life
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces stress concentrations and leakage by effectively balancing centrifugal forces, increasing the design life of the blade and minimizing contamination of coolant air.
Implementation Method 1
the greatest mechanical stress is the centrifugal force on the blade attachments, which can be 70,000 lbs or more per blade
Data Source
AI summary
A turbine blade airfoil (32) with a center of mass (ACM) that is laterally offset from the center of mass (PCM) of a platform (42) to which the airfoil is attached. Respective offsets (da, dp) balance these centers of mass (ACM, PCM) about an attachment plane (64) of the blade root (30), providing balanced centrifugal loading on opposite lobes (51, 52) or other attachment surfaces of the root. The attachment plane (64) may be a plane of bilateral symmetry of the root, and/or it may include an attachment axis (65) that passes through the root center of mass (RCM) along a radius of rotation of the airfoil. The airfoil and platform centers of mass (ACM, PCM) may be dynamically balanced about the attachment axis (65) and/or the attachment plane (64).