CMC End Face Seals for Turbine Engine Thermal Growth Gaps
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Solution Overview
Problem
Gas turbine engines with components made from materials having different coefficients of thermal expansion face challenges in maintaining effective seals due to differential thermal growth, leading to leakage issues and potential damage from close assembly at ambient temperatures.
Innovation Solution
The use of ceramic matrix composite materials with T-shaped, H-shaped, or wedge-shaped seals that incorporate radial and outer segments, along with flow discouragers, to block gas flow between components, leveraging secondary air pressure for seal closure and accommodating thermal expansion differences without close proximity assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If components are made from materials with different coefficients of thermal expansion, then thermal efficiency is improved, but seal effectiveness deteriorates due to differential thermal growth
Solution Approach 1:
The seal is divided into multiple segments including an outer segment, radial segments, and inner segments. This segmentation allows each portion to independently accommodate thermal expansion differences between CMC components while maintaining the overall sealing function, resolving the contradiction between thermal efficiency and seal effectiveness.
Solution Approach 2:
The seal design incorporates geometric parameters such as arc lengths, radial distances, and angles that are specifically optimized to accommodate differential thermal growth. The outer segment spans an arc that accommodates expansion, while radial segments position seals at optimized distances from the axis, allowing the seal geometry to adapt to thermal parameter changes without losing effectiveness.
2Manufacturing precision
If components are assembled in close proximity, then manufacturing precision is improved, but damage risk increases due to thermal expansion differences
Solution Approach 1:
The seal structure is pre-configured with specific geometric relationships (arc lengths, radial distances, angles) that anticipate and accommodate thermal expansion before it occurs. This preliminary design allows components to be assembled with appropriate clearances that automatically adjust during thermal cycling, maintaining precision while preventing damage.
Solution Approach 2:
The seal acts as an intermediary element between CMC components, absorbing and accommodating the stresses from differential thermal expansion. This mediator allows components to maintain close proximity for manufacturing precision while preventing direct contact that would cause damage during thermal expansion.
3Ease of manufacture
If seal geometry is simplified, then ease of manufacture is improved, but adaptability to thermal growth deteriorates
Solution Approach 1:
The seal incorporates different geometric characteristics in different regions: the outer segment has a specific arc length for thermal accommodation, radial segments have optimized distances from the axis, and inner segments have specific angular positions. This local differentiation allows each portion to perform its specific function while maintaining overall manufacturability through consistent material properties and fabrication processes.
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 solution effectively reduces leakage flow between ceramic matrix composite components, maintains seal integrity under thermal expansion, and avoids the need for close assembly, reducing the risk of damage and improving thermal efficiency.
Implementation Method 1
leveraging secondary air pressure for seal closure
Implementation Method 2
components made from materials that have different coefficients of thermal expansion. Due to the differing coefficients of thermal expansion, the components expand at different rates during operation
Data Source
AI summary
A gas turbine engine assembly includes a first component, a second component, and a seal. The first component is spaced apart from the second component to form a gap between the first component and the second component. The seal is configured to block gases from flowing in the gap between the first component and the second component.