Steam Turbine Rotor Blade Plug-in Root Shoulder Design
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Solution Overview
Problem
Rotor blades with plug-in roots in turbomachines, particularly steam turbines, face challenges in withstanding high centrifugal forces and axial and circumferential forces from the flowing medium, leading to stress issues during operation.
Innovation Solution
The design of a rotor blade with a plug-in root featuring a central lobe and two edge lobes, where the axial sides of the first and second sections have a shoulder that reduces the axial extension, and the ratio of radial heights to the overall axial width is optimized to enhance force absorption, with specific ratios for the radial heights of the first and second sections and the total radial height to the total axial width, allowing for increased force absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a plug-in foot with lobes is used to attach rotor blades, then the attachment structure is established, but the forces that can be absorbed are insufficient under high operational stresses
Solution Approach 1:
The plug-in foot is divided into multiple lobes (typically three) with distinct sections. Each lobe contains a radially outer first section and a radially inner second section separated by a shoulder. This segmentation allows different sections to bear different types of loads, with the first section primarily handling radial centrifugal forces and the second section handling axial and circumferential forces from the flowing medium.
Solution Approach 2:
Different sections of the plug-in foot are given different geometric properties to optimize local stress distribution. The first section has a greater axial extension than the second section, creating a stepped configuration. This local variation in geometry allows the structure to better distribute and absorb the complex multi-directional forces experienced during operation.
2Strength
If the radial heights and axial extensions of lobe sections are optimized with specific ratios, then the force absorption is significantly increased, but the manufacturing precision requirements are heightened
Solution Approach 1:
The invention specifies optimal parameter ranges for the plug-in foot geometry to maximize force absorption. The ratio of the axial extension of the first section to the overall axial width is recommended to be between 0.39 and 0.45, and the ratio of the axial extension of the second section to the overall axial width is recommended to be between 0.40 and 0.46. These parameter optimizations ensure balanced stress distribution across all sections.
Solution Approach 2:
The plug-in foot employs an asymmetric stepped design where the first section extends further axially than the second section. This asymmetric configuration is deliberately designed to match the asymmetric distribution of forces experienced during operation, with the longer first section better positioned to handle radial centrifugal forces while the shorter second section manages axial and circumferential loads.
Data Source
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AI summary
A rotor blade for a flow machine, in particular a steam turbine, includes an insertion root with a first finger and two second fingers which are arranged on either side of the first finger in axial direction. The first finger and the second fingers have a shoulder in axial direction on axial sides facing one another such that the fingers have a radially outer first portion and a radially inner second portion whose axial extension is shorter than that of the outer, first portion. In relation to a total axial width between axial sides of the two second fingers which face away from one another, the radial height of the first, radially outer portion is in the range of 0.39 to 0.45, particularly 0.40 to 0.44, and the radial height of the second, radially inner portion is between 0.40 and 0.46, particularly between 0.41 and 0.45.