CMC Clearance Control Ring for Gas Turbine Seal Leakage
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Solution Overview
Problem
The challenge in gas turbine engines is to minimize seal leakages and clearance between rotor and stator components due to thermal and mechanical growth, which affects performance and fuel efficiency, particularly during transient conditions like takeoff acceleration.
Innovation Solution
Implementing a passive clearance control ring made of ceramic matrix composites (CMCs) with a low coefficient of thermal expansion to limit the thermal expansion of stator components, thereby maintaining tight seals and reducing parasitic leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stator components are used, then the engine structure is simple and easy to manufacture, but thermal expansion increases rotor/stator clearances during operation, causing seal leakage and reduced performance
Solution Approach 1:
The patent changes the thermal expansion parameter by using a control ring made of Invar alloy, which has a coefficient of thermal expansion matched to the rotor component. This parameter change allows the control ring to maintain consistent dimensions with the rotor across temperature variations, preventing clearance increases and seal leakage without requiring complex active control systems
Solution Approach 2:
The control ring acts as an intermediary component between the stator and rotor. It is disposed radially outward of the stator component and works to limit the relative thermal expansion between the stator and rotor, thereby controlling the clearance without directly interfering with the primary gas flow path or requiring complex mechanical linkages
2Productivity
If passive clearance control rings are added to limit thermal expansion, then rotor/stator clearances are reduced and seal leakage is minimized, but the engine structure becomes more complex
Solution Approach 1:
The control ring provides self-service clearance control through its unique thermal expansion properties. The Invar alloy automatically compensates for thermal expansion differences between the stator and rotor across the operating temperature range, maintaining optimal clearances without requiring external control systems, actuators, or complex mechanical mechanisms
Solution Approach 2:
The patent employs composite material strategy by using Invar alloy for the control ring, which combines the properties of low thermal expansion with adequate mechanical strength and thermal stability. This material selection allows the control ring to function effectively in the high-temperature turbine environment while maintaining its dimensional stability relative to the rotor
3Manufacturing precision
If CMCs are used for the control ring, then thermal expansion is effectively inhibited and clearances are minimized, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the material parameter from conventional metals to CMCs, which have fundamentally different thermal expansion characteristics. CMCs can be engineered to have near-zero or negative thermal expansion coefficients, providing superior clearance control precision. The manufacturing complexity is managed through established CMC fabrication processes such as chemical vapor infiltration (CVI) and polymer impregnation and pyrolysis (PIP)
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
The use of CMCs effectively inhibits thermal expansion of stator components, reducing rotor/stator clearances and improving engine performance by minimizing air flow leakage and lowering exhaust gas temperature overshoot.
Implementation Method 1
the clearance control ring having a coefficient of thermal expansion which is lower than the at least a portion of the stator component and, the at least a portion of the stator component is limited from thermal expansion
Data Source
AI summary
A passive clearance control limits thermal expansion between stator components relative to rotor components. A control ring controls clearance in a passive manner and is located on or adjacent to stationary components which thermally expand during engine operation. The control ring is formed of material having low coefficient of thermal expansion such as CMCs (Ceramic Matrix Composites) and therefore limits, inhibits or restrains expansion of the adjacent stator components as temperatures increase. Limiting expansion of the stator component reduces rotor/stator clearances and limits parasitic leakage of fluid along the flow path through the engine core.