Steam Turbine Blade Root Orientation for Stress Reduction
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Solution Overview
Problem
The existing steam turbine blades with axially-inserted fir tree type blade roots experience high peak stresses and fretting fatigue due to centrifugal forces, limiting the number of blades that can be attached and reducing fatigue life, especially when the blade root is inserted at an angle greater than 0° relative to the axial direction of the turbine rotor.
Innovation Solution
The steam turbine blade design features a blade root with hooks in multiple stages, oriented at a predetermined angle α greater than 0° relative to the axial direction, and a platform between the airfoil and blade root, with specific angle settings for α and θ to reduce peak stresses and prevent fretting fatigue by ensuring relative slide between contact surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the blade root is inserted at an angle greater than 0° relative to the axial direction to increase the number of blades, then the number of blades that can be attached increases, but high peak stresses are generated in the notches formed in the blade root and blade groove
Solution Approach 1:
The invention changes the insertion angle parameter of the blade root from the conventional 0° (axial direction) to a specific angle range (10°-45°) relative to the axial direction. This parameter change allows more blades to be arranged in the restricted outer peripheral region while the specific angle range is optimized to control peak stress generation in the notches
Solution Approach 2:
The invention introduces asymmetric insertion orientation of the blade root relative to the axial direction of the turbine rotor. Instead of symmetric axial insertion (0°), the blade root is inserted at an asymmetric angle (10°-45°), which changes the stress distribution pattern and enables increased blade count while managing peak stresses through the specific angular orientation
2Quantity of substance
If the blade root is inserted at an angle greater than 0° to increase blade density, then more blades can be attached, but fretting fatigue occurs at the contact surfaces of the blade root and blade groove
Solution Approach 1:
The invention optimizes the insertion angle parameter to a specific range (10°-45°) that simultaneously achieves increased blade density and reduced fretting fatigue. This parameter optimization ensures that contact surfaces maintain relative slide under centrifugal forces, preventing fretting fatigue while accommodating more blades
Solution Approach 2:
The invention utilizes the dynamic effect of centrifugal forces during turbine operation to create relative slide between the contact surfaces of the blade root and blade groove. This relative motion prevents fretting fatigue by avoiding static contact, and the specific insertion angle (10°-45°) is designed to maximize this beneficial dynamic effect
3Area of stationary object
If the blade root is inserted at an angle greater than 0° to maximize blade attachment, then the outer peripheral region is utilized more efficiently, but the fatigue life is reduced due to increased peak stresses
Solution Approach 1:
The invention changes the insertion angle parameter to a specific optimized range (10°-45°) that balances two competing objectives: maximizing the utilization of the outer peripheral region (enabling more blades) and controlling peak stress levels to maintain fatigue life. This specific parameter range represents the optimal compromise between spatial utilization and durability
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 allows for a larger number of blades to be attached in a restricted outer peripheral region while suppressing peak stresses and fretting fatigue, extending the fatigue life of the turbine blades and improving their reliability.
Implementation Method 1
Centrifugal forces acting on the whole of the turbine blade are mostly supported at serrations of the blade root 4 and the blade groove 5
Data Source
AI summary
A steam turbine blade in which the turbine blade has a blade root of the axially-inserted fir tree type and a larger number of turbine blades can be attached in a restricted outer peripheral region of a turbine rotor by arranging the blade root to be oriented in a direction forming a predetermined angle α larger than 0° relative to the axial direction of the turbine rotor. The steam turbine blade can suppress peak stresses generated at the bottoms of notches formed in the blade root and a blade groove and also suppress fretting fatigue from being induced by contact between peak stress generating areas and areas opposed to the peak stress generating areas at the notch bottoms. The steam turbine blade includes an airfoil, and a blade root attached to a turbine rotor and having plural stages of hooks in the radial direction of the turbine rotor.