Turbine Blade Shroud Indentation for Frequency Stability

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Solution Overview

Problem

Existing turbomachine blade designs face challenges in avoiding excitation of natural frequencies and resonant behavior, which can lead to harmful operational impacts, particularly with stiffer blade profiles and increased twist angles causing stress and assembly difficulties.

Innovation Solution

The introduction of an indentation along the contact face of shrouded blades, which splits the original contact area into two separate areas, increasing frequency stability by altering the contact points between adjacent shroud segments.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If stiffer blade profiles and increased twist angles are used to avoid resonant behavior, then the natural frequencies of the blades are increased, but the stresses in the blades increase and assembly becomes more difficult

Engineering Contradiction:

Improveavoidance of resonant behaviorVSAvoidblade stress

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent introduces an indentation parameter (depth, position, shape) on the shroud contact face to modify the contact characteristics between adjacent blades. This changes the effective contact area and contact pressure distribution, thereby altering the vibrational characteristics and natural frequencies of the blade without requiring increased blade stiffness or twist angle that would lead to higher stresses

Inventive Principle:

Principle #35Parameter changes

2Reliability

If stiffer blade profiles and increased twist angles are used to avoid resonant behavior, then the natural frequencies of the blades are increased, but the difficulty of assembling the blade row increases

Engineering Contradiction:

Improveavoidance of resonant behaviorVSAvoidassembly difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The indentation on the shroud contact face modifies the contact mechanics between adjacent blades, allowing for frequency adjustment without increasing pre-stress. This enables easier assembly compared to highly pre-stressed blades, while still achieving the goal of avoiding resonant behavior during operation

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If the contact area between adjacent shrouds is concentrated at one location, then the assembly is simpler, but the frequency stability at higher nodal diameters is reduced

Engineering Contradiction:

Improvecontact area configurationVSAvoidfrequency stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent segments the originally concentrated contact area into multiple contact regions by introducing an indentation. This creates separate contact zones on the shroud contact face, which distributes the contact forces and improves frequency stability at higher nodal diameters while maintaining reasonable assembly complexity

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS10006296B2Shroud for pre-twisted airfoils

Publication Date: 2018.06.26 GE VERNOVA INFRASTRUCTURE TECHNOLOGY LLC

AI summary

A method and a blade for a turbine or, more generally a turbomachine, are described with the blade having at a top end a shroud segment designed to engage with shroud segments of adjacent blades in an ring-shaped assembly at least partly by means of assembling the blades with the shroud segment having a central indentation along an engaging face.