Steam Turbine Blade Root Hook Geometry for Stress Reduction
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Solution Overview
Problem
Conventional attachment arrangements for steam turbine blades experience high local and average stresses due to centrifugal loading and vibration, leading to potential fatigue issues and reduced lifespan, especially in low-pressure steam turbines with larger blades and stress corrosion from moisture.
Innovation Solution
A blade attachment configuration featuring a blade root with optimized hook and neck structures, including slanted contact surfaces and larger fillet radii, which reduces stress concentrations and distributes loads more evenly across the contact areas between the blade root and rotor disc.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional tangs and grooves are used to attach the blade root to the rotor disc, then the blade can be securely mounted, but high local and average stresses occur due to centrifugal loading
Solution Approach 1:
The patent applies curvature by replacing the conventional sharp-angled tangs and grooves with curved hook shapes. The hooks have rounded contact surfaces that distribute centrifugal loads more evenly, reducing stress concentrations at the attachment interface between blade root and rotor disc
Solution Approach 2:
The patent modifies the local geometry of the attachment interface by creating optimized contact surfaces on the hooks with specific angles and curvatures. This local quality change ensures that stresses are distributed more uniformly across the contact areas, preventing localized stress concentrations while maintaining secure attachment
2Length of moving object
If the blade length is increased to meet demand for longer rotating blades, then more power can be generated, but the blades operate under even higher loads leading to increased stresses
Solution Approach 1:
The curved hook geometry with optimized contact surfaces allows longer blades to be attached to the rotor disc while distributing the increased centrifugal loads more effectively. The rounded surfaces prevent stress concentrations that would otherwise limit blade length increases
Solution Approach 2:
The patent transitions from a conventional linear tang-groove interface to a three-dimensional hooked interface with optimized contact surface angles. This dimensional change in the attachment geometry enables better load distribution for longer, heavier blades
3Power
If the rotational speed is increased to generate more power, then the energy output increases, but the centrifugal loading on the blades and rotor increases significantly
Solution Approach 1:
The curved hook attachment geometry with optimized contact surfaces distributes the centrifugal forces generated at high rotational speeds more evenly across the blade root and rotor disc interface, enabling higher operating speeds without excessive stress concentrations
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 configuration minimizes local and average stresses, enhancing the fatigue life of the rotor and blades by reducing stress concentrations and allowing for increased blade lengths under higher loads while maintaining low shear stresses.
Implementation Method 1
the centrifugal load on the blade, which is very high due to the high rotational speed of the rotor
Data Source
AI summary
A blade is mountable to a disc. The blade comprises a blade platform and a blade root extending from the blade platform. The blade root comprises a first hook and a second hook, a first neck between the first hook and the blade platform, and a second neck between the first hook and the second hook. Each hook comprises a contact surface and a non-contact surface. An angle between each contact surface and each non-contact surface is optimized to reduce local stresses.