Turbine Impeller Cutaway for Stress Decoupling
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Solution Overview
Problem
High thermal and mechanical stresses due to rapid heating and cooling during transient operations in turbine engines reduce the fatigue life of impeller wheels by causing damage at the inner diameter, where compressive and tensile stresses interact.
Innovation Solution
A rotating component with an impeller wheel featuring radially inwardly facing vanes that include a cutaway portion, forming grooves and reducing stress interactions through decoupling thermal responses, which can be implemented in new or existing turbine engines via machining processes like EDM, milling, or abrading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If impeller vanes are used to direct secondary flow during transient operations, then fluid flow control is improved, but thermal and mechanical stresses increase due to rapid heating and cooling
Solution Approach 1:
The impeller vane is segmented into two distinct surfaces: a radially outwardly facing vane surface and a radially inwardly facing vane surface. This segmentation allows each surface to independently manage different stress types, with the cutaway portion creating a physical separation between thermal stress zones and mechanical stress zones, thereby reducing the interaction between these stress types while maintaining fluid flow control functionality.
Solution Approach 2:
The cutaway portion is strategically positioned at the radially inwardly facing vane surface to create a localized structural modification. This local quality change allows the region to have different thermal and mechanical properties compared to the rest of the vane, specifically reducing thermal stress concentration at the inner diameter while preserving the overall structural integrity and fluid directing capability.
2Productivity
If impeller vanes direct fluid flow from outer to inner diameter, then fluid flow efficiency is improved, but damage occurs at the inner diameter due to stress interaction
Solution Approach 1:
The cutaway portion segments the impeller vane structure, creating distinct zones for thermal stress management and mechanical stress management. This segmentation prevents the concentration of both stress types at the vulnerable inner diameter region, thereby extending fatigue life while preserving the grooves' ability to direct fluid flow efficiently from outer to inner diameter.
Solution Approach 2:
The cutaway portion converts the harmful effect of thermal stress concentration into a beneficial feature by creating a stress-relief geometry. The cutaway design transforms the inner diameter region from a stress concentration point into a stress distribution zone, where thermal stresses are reduced and mechanical stresses are better managed, thereby improving reliability without sacrificing productivity.
3Stress or pressure
If cutaway portion is added to impeller vane, then stress interaction is reduced, but manufacturing complexity increases
Solution Approach 1:
The cutaway portion is designed with specific geometric parameters (depth, width, and positioning) that can be optimized to achieve the desired stress reduction while minimizing manufacturing complexity. By carefully controlling these parameters, the cutaway can be formed using standard machining operations, balancing the benefit of reduced stress interaction with the cost of increased manufacturing steps.
Data Source
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AI summary
A rotating component (10) of a turbine engine is provided and includes a wheel (11) having a face (14) to which fluid flow is provided and a plurality of impeller vanes (20) forming a plurality of grooves (30) along which the fluid flow is directed from an outer to an inner diameter of the wheel face (14), at least one of the plurality of the impeller vanes (20) including a radially inwardly facing vane surface (21) formed to define a cutaway portion (40).