Blade Wedge Attachment for Gas Turbine Stress Mitigation

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Solution Overview

Problem

Rotors in gas turbine engines face stress concentration issues at the narrow neck and fillet of turbine blades due to operational stresses, which can lead to delamination in multi-layer fiber structures and other material failures.

Innovation Solution

The use of free-floating wedges with specific geometric and material properties, including ceramic materials and coatings, is implemented to compress the narrow fillet and mitigate tensile stresses by distributing compressive pressure effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If the blade root is joined through a narrow neck and fillet to the airfoil, then the blade structure is compact and fits in the slot, but stress concentration occurs at the neck and fillet during operation

Engineering Contradiction:

Improveblade root geometryVSAvoidstress resistance at neck and fillet

Core Design Contradiction:

ShapeVSStrength

Solution Approach 1:

The blade root is divided into separate components: a head portion, a neck portion, and a fillet portion. Wedge members are inserted into circumferential gaps between these segmented portions, allowing independent stress management at each location. The wedges apply localized compressive forces to counteract tensile stresses at the neck and fillet without requiring a monolithic structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Wedge members are strategically positioned at specific locations where stress concentration occurs (at the neck and fillet regions). Each wedge has a specific geometry designed to apply compressive force locally at its corresponding gap location. This localized intervention strengthens only the critical stress areas without adding unnecessary material or complexity to the entire blade structure.

Inventive Principle:

Principle #3Local quality

2Strength

If pads are secured near the neck and fillet to mitigate stress, then stress concentration is reduced, but the device complexity increases

Engineering Contradiction:

Improvestress resistance at neck and filletVSAvoidnumber of additional components

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The wedge members serve multiple functions simultaneously: they act as stress-mitigating pads at the neck and fillet regions, and they also function as retention elements that help secure the blade in the slot. The same components that reduce stress concentration also contribute to blade retention, eliminating the need for separate retention mechanisms and reducing overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The stress mitigation function and blade retention function are merged into a single integrated system. The wedge members are positioned to simultaneously address stress concentration at the neck/fillet and provide retention assistance. This consolidation reduces the number of separate components compared to using dedicated pads plus separate retention mechanisms.

Inventive Principle:

Principle #5Merging (Combining)

3Adaptability or versatility

If circumferential gaps are maintained between blade roots and slot sides, then thermal expansion and manufacturing tolerances are accommodated, but stress mitigation effectiveness is reduced

Engineering Contradiction:

Improveaccommodation of thermal expansion and tolerancesVSAvoidstress mitigation at neck and fillet

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

Wedge members are introduced as intermediary elements that fill the circumferential gaps between the blade root and slot sides. These wedges act as mediators that transmit and distribute compressive forces from the slot structure to the blade's neck and fillet regions. The wedges maintain the necessary gaps for thermal expansion while simultaneously providing the stress mitigation function through their positioning and geometry.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The stress mitigation function is extracted from the monolithic blade structure and implemented as separate, removable wedge members. This extraction allows the wedges to be independently positioned in the circumferential gaps to provide both gap-filling for tolerance accommodation and localized stress mitigation. The separable nature of the wedges allows optimization of their geometry for stress mitigation without compromising the gap requirements.

Inventive Principle:

Principle #2Taking out (Extraction)

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 solution reduces stress concentration at the narrow fillet, limiting delamination in multi-layer fiber structures and enhancing the structural integrity of turbine blades during operation.

Implementation Method 1

The relatively thick portion is operable as a wedge to compress the narrow fillet upon rotation of the disk

Methodology Applied

Scientific EffectCompressive pressure distribution: Compression

Data Source

PatentUS9611746B2Blade wedge attachment

Publication Date: 2017.04.04 RTX CORP

AI summary

A rotor includes a disk that has slots circumferentially arranged around its periphery. Blades include respective roots that are mounted in respective ones of the slots. The roots are smaller than the slots such that there are circumferential gaps between the roots and circumferential sides of the slots. Wedges are respectively located within the circumferential gaps. The wedges are free floating with regard to the blades and the disk.