Turbine Bucket Root Design for Centrifugal Stress and Vibration Control
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Solution Overview
Problem
Increased length of turbine buckets in low-pressure steam turbines leads to high centrifugal stress on blades and dovetails, and vibration issues due to reduced rigidity and inadequate steam passage design.
Innovation Solution
The turbine bucket design features a blade root with a suction surface and pressure surface formed into three areas, including a steam inlet side with curvature, a steam outlet side with curvature, and a straight area between, along with a dovetail inserted into straightly cut grooves, enhancing steam passage and reducing centrifugal stress and vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the blade length is increased to increase the exhaust area, then the power output is improved, but the centrifugal stress on the blade and dovetail becomes excessive
Solution Approach 1:
The blade root cross-section is designed with non-uniform distribution, concentrating material where centrifugal stress is highest (near the dovetail) and reducing material where stress is lower. This local optimization allows the blade to withstand high centrifugal forces without requiring uniform thickening throughout the entire blade length, thus maintaining power output while controlling stress levels.
Solution Approach 2:
The invention changes the geometric parameters of the blade root cross-section, specifically defining the suction surface and pressure surface with specific curvature relationships. By parameterizing the cross-sectional shape with equations that relate the suction and pressure surface radii of curvature, the design optimizes the stress distribution to keep centrifugal stress within material limits while maintaining the required blade length for high power output.
2Power
If the blade length is increased to increase the exhaust area, then the power output is improved, but the steam passage width becomes insufficient
Solution Approach 1:
The blade root cross-section employs non-uniform thickness distribution, with thinner sections positioned to preserve steam passage width and thicker sections positioned where structural strength is most needed. This localized differentiation allows the design to maintain adequate steam flow area while providing sufficient material where centrifugal stress requires it, thereby achieving both high power output and adequate steam passage dimensions.
3Power
If the blade length is increased to increase the exhaust area, then the power output is improved, but the vibration response increases due to reduced rigidity
Solution Approach 1:
The invention optimizes the geometric parameters of the blade root cross-section, specifically the relationship between suction surface radius of curvature (R1) and pressure surface radius of curvature (R2), where R1/R2 is maintained between 0.8 and 1.2. This parameter optimization enhances the blade's bending stiffness and natural frequency, thereby reducing vibration response while maintaining the increased blade length necessary for high power output in the low-pressure final stage turbine.
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 design ensures centrifugal stress remains within material limits, maintains a sufficient steam passage, and reduces vibration response, achieving an exhaust area exceeding 9.6 m² for 3600 rpm machines and 13.8 m² for 3000 rpm machines while providing superior damping characteristics.
Implementation Method 1
a blade portion of a turbine bucket has a suction surface and a pressure surface which are each formed, at a turbine blade root, of three areas consisting of a steam inlet side area with curvature, a steam outlet side area with curvature, and an area put between the two areas
Implementation Method 2
a turbine bucket that can make centrifugal stress acting on a blade portion or dovetail not greater than a limit value of a material
Data Source
AI summary
A turbine bucket for a steam turbine low-pressure final stage has an exhaust area exceeding 9.6 m2 and 13.8 m2 in steam-turbine final-stage buckets for a rated speed 3600 rpm and 300 rpm machines, respectively. The turbine bucket is made of martensite steel. A blade portion of the turbine bucket has a suction surface 7 and a pressure surface 8 which are each formed, at a turbine blade root, of three areas consisting of a steam inlet side area 12 with curvature, a steam outlet side area 13 with curvature and an approximately straightly formed area located between the two areas.