Free-floating Damping Inserts for Shrouded Turbine Blades
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Solution Overview
Problem
Conventional shrouded turbine blades face challenges in maintaining effective damping over a wide operating range due to manufacturing tolerances and are susceptible to damage at low rotational speeds, with high temperature creep affecting the contact load between shrouds, leading to high vibratory stresses.
Innovation Solution
The implementation of damping inserts within the shrouds of turbine blades, which are free-floating and guided by the shape of the carrier shroud pockets, engage with the lid shroud of neighboring blades to provide mechanical damping, reducing dependence on precise shroud-to-shroud contact and controlling contact load through adjustable mass and geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the shroud gap is increased to maintain low contact load for damping, then energy dissipation is improved, but the blades become susceptible to damage at low rotational speeds due to lock up
Solution Approach 1:
A damping insert is introduced as an intermediary element between the carrier shroud and lid shroud. The insert engages with both shrouds to provide controlled contact and energy dissipation, preventing direct shroud-to-shroud contact that causes lock up while maintaining effective damping through the insert's controlled engagement and disengagement
Solution Approach 2:
The contact load parameters are changed by using a damping insert with specific mass and geometric properties. The insert's dimensions, material density, and engagement geometry are designed to provide appropriate contact force across the operating range, transforming the rigid shroud contact into a controlled, speed-dependent interaction
2Reliability
If precise machining and assembly are performed to maintain contact load, then damping effectiveness is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The damping insert is designed to self-adjust its engagement with the shrouds based on rotational speed and centrifugal forces. The insert automatically finds its optimal contact position and engagement force without requiring precise pre-setting of shroud gaps or contact loads, making the system self-regulating across the operating range
Solution Approach 2:
The design shifts from controlling geometric parameters (shroud gap, contact load) to controlling material and inertial parameters (insert mass, geometry). This allows tolerance stack-up to be absorbed by the insert's design parameters rather than requiring tight machining tolerances on the shrouds themselves
3Reliability
If the contact load is maintained for effective damping, then vibration reduction is improved, but high temperature creep affects the contact load over time, reducing damping
Solution Approach 1:
The damping insert system is self-regulating through centrifugal forces. As the rotor spins, centrifugal force automatically maintains the insert's engagement with the shrouds, compensating for any creep-induced changes in shroud geometry or position. The system adapts to thermal and mechanical changes without external intervention
Solution Approach 2:
The contact load is made dynamic rather than static. The insert's engagement force varies with rotational speed, automatically increasing under higher centrifugal loads and maintaining consistent damping performance. This dynamic adjustment compensates for creep effects that would otherwise cause contact load drift
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 solution ensures consistent damping across a wide range of rotational speeds, reduces the risk of blade damage, and allows for more relaxed manufacturing tolerances, enhancing the durability and operational efficiency of turbine blades.
Implementation Method 1
The damping inserts are configured to dampen vibrations of the blades during rotation of the blades and the rotor disk via engaging an interior surface within the corresponding pocket of the carrier shroud and engaging the distal end of the lid shroud of the neighboring blade
Implementation Method 2
A contact force applied by each damping insert on the distal end of the lid shroud of the neighboring blade is based on a rotational speed of the blades and the rotor disk
Data Source
AI summary
A rotor assembly includes plural blades and damping inserts. The blades include a carrier shroud and a lid shroud extending from an airfoil of the respective blade in generally opposite directions. The carrier shrouds define pockets at distal ends thereof. The damping inserts are disposed in the pockets of the carrier shrouds of the blades and free-floating within the pockets. The damping inserts are configured to dampen vibrations of the blades during rotation of the blades and the rotor disk via engaging an interior surface within the corresponding pocket of the carrier shroud and engaging a distal end of the lid shroud of the neighboring blade. A contact force applied by each damping insert on the distal end of the lid shroud of the neighboring blade is based on a rotational speed of the blades and the rotor disk.