Dynamic Tip Clearance Control for Shrouded Gas Turbine Blades
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Solution Overview
Problem
Gas turbine engines face challenges in maintaining optimal tip clearance between shrouded blades and stator structures, particularly during transient conditions, as existing solutions either allow excessive leakage or risk rubs due to fixed clearance settings.
Innovation Solution
A turbine bucket tip clearance control system that allows axial shifting of the rotor and stator assemblies relative to each other, enabling selective adjustment of the clearance gap between seal teeth and stator surfaces, using radially inwardly facing axially-stepped surfaces and radially outwardly projecting seal teeth to optimize leakage reduction and prevent rubs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed clearance is maintained between the shroud tooth and stator structure, then rubs are prevented during transient conditions, but leakage increases during normal operation
Solution Approach 1:
The clearance between the seal tooth and stator is made dynamically adjustable through axial shifting of the rotor assembly. During transient conditions, the rotor shifts to provide a larger clearance to prevent rubs. During normal operation, the rotor shifts to reduce the clearance and minimize leakage, thus resolving the contradiction between reliability and energy loss.
2Loss of energy
If the clearance is reduced to minimize leakage, then energy loss decreases, but the risk of rubs increases during transient conditions
Solution Approach 1:
The system dynamically adjusts the clearance based on operational conditions. During normal operation, the rotor position provides a reduced clearance to minimize leakage. During transient conditions such as start-up and shut-down, the rotor shifts axially to increase the clearance and prevent rubs, thus resolving the contradiction between energy loss and reliability.
3Loss of energy
If axial shifting is implemented to adjust clearance dynamically, then leakage is minimized during normal operation, but device complexity increases
Solution Approach 1:
The axial shifting mechanism is designed to utilize the existing thermal expansion and contraction of the rotor assembly during operation. The rotor naturally shifts axially in response to temperature changes, providing automatic clearance adjustment without requiring external control systems or additional actuators, thus minimizing the increase in device complexity while achieving leakage reduction.
Data Source
AI summary
A turbine bucket tip clearance control system includes a rotor assembly having a rotor supporting a plurality of axially spaced wheels, each wheel mounting an annular row of buckets, the annular row of buckets on at least one of the plurality of axially-spaced wheels having a radially outer tip shroud provided with at least one seal tooth. A stator assembly includes a radially inwardly facing, axially-stepped surface, formed with radially inner and outer seal surfaces connected by a shoulder. The stator assembly and rotor assembly are moveable axially relative to each other, enabling selective positioning of the at least one seal tooth radially opposite one of the radially inner and outer seal surfaces to thereby selectively alter a clearance gap between the at least one seal tooth and the radially inward facing axially-stepped surface.