Integrally Bladed Rotor Rim Segmentation for Thermal Fatigue
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Solution Overview
Problem
Hoop stresses caused by thermal fatigue reduce the lifespan of integrally bladed rotors in gas turbine engines, particularly affecting the outer rim.
Innovation Solution
The introduction of discontinuities between adjacent blades, angled relative to the chord line, and radially inward channels with flat portions, which relieve stress at the leading and trailing edges of the blades, and the use of seals to prevent gas recirculation, while softening the edges of the blades to reduce stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the outer rim is made continuous to support blade loads, then structural strength is improved, but thermal fatigue stress increases due to hoop stresses
Solution Approach 1:
The continuous outer rim is segmented by introducing discontinuities that extend radially inward between adjacent blades. These discontinuities divide the rim into separate sections, allowing thermal expansion and contraction without generating excessive hoop stresses, while still maintaining structural integrity through seals between the segments.
Solution Approach 2:
Seals are introduced as intermediary elements between the discontinuous rim segments. These seals prevent gas recirculation across the discontinuities while allowing the segments to move independently, thus maintaining both structural strength and thermal fatigue resistance.
2Reliability
If the outer rim is made discontinuous to reduce thermal fatigue stress, then thermal fatigue resistance is improved, but structural strength decreases
Solution Approach 1:
Seals are introduced as intermediary elements between the discontinuous rim segments. These seals prevent gas recirculation across the discontinuities while allowing the segments to move independently, thus maintaining both structural strength and thermal fatigue resistance.
Solution Approach 2:
The discontinuities are positioned and dimensioned with specific parameters (extending radially inward between blades, angled relative to chord line) to optimize both stress relief and structural strength. The geometry of discontinuities and seals is carefully controlled to balance thermal fatigue resistance with load-bearing capacity.
3Reliability
If seals are added to prevent gas recirculation, then operational reliability is improved, but device complexity increases
Solution Approach 1:
The seals are merged with the rim structure itself, forming an integrated component rather than separate add-on parts. The discontinuities and seals are formed as part of the same manufacturing process, reducing assembly steps and overall device complexity while maintaining reliability benefits.
Data Source
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AI summary
An integrally bladed rotor has an outer rim with a plurality of blades extending radially outwardly of the outer rim. A plurality of channels are formed radially inwardly of the outer rim. A discontinuity formed at a radially outer surface of the outer rim includes a first thin slot at a radially outer face of the outer rim with an enlarged seal holding area. A second thin slot is positioned radially inwardly of the seal holding. The first and second thin slots are thinner circumferentially than the enlarged seal holding area. A seal is inserted into the seal holding area. The seal does not extend into the first and second thin slots, nor into the channels.