Flow Path Flex Seal and Heat Shield for Turbine Thermal Growth
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Solution Overview
Problem
Gas turbine engines face challenges in effectively sealing interfaces between static frames and flowpath fairings due to recirculating air and thermal growth, leading to windage and leakage issues, particularly in hot sections where material limitations and packaging constraints hinder the use of conventional seals.
Innovation Solution
A combination of a flex seal with axial convolutions and a heat shield is used in the cooling air flowpath, where the flex seal is made of a high fatigue limit material like INCO 718 and the heat shield of a high maximum use temperature material like INCO 625, with a purge airflow system to prevent backflow and accommodate thermal deflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional seal is used at the interface between static frames and flowpath fairings, then sealing is provided, but the seal cannot accommodate thermal growth and material limitations occur in hot sections
Solution Approach 1:
The patent employs a flex seal with axial convolutions that can flex and deform to accommodate thermal growth between the static frame and flowpath fairing. The convoluted structure allows the seal to expand and contract with temperature changes while maintaining sealing effectiveness, resolving the contradiction between temperature resistance and seal integrity.
Solution Approach 2:
The seal's physical parameters (shape, volume, position) are allowed to change in response to thermal conditions. The axial convolutions enable the seal to undergo controlled deformation as temperature varies, adapting to thermal growth without compromising sealing reliability in hot sections.
2Reliability
If cooling air is used to seal the interface, then sealing is provided, but recirculating air causes windage and leakage issues
Solution Approach 1:
The patent extracts the harmful recirculating air from the sealing interface by providing a dedicated seal cavity that isolates the sealing function from the cooling air flowpath. This prevents the cooling air from recirculating and creating windage, while still providing effective sealing at the interface.
Solution Approach 2:
The sealing function is segmented from the cooling air flowpath by creating a separate seal cavity. This segmentation allows the seal to operate independently without being affected by the cooling air circulation, eliminating windage while maintaining sealing effectiveness.
3Reliability
If a rigid seal is used to prevent backflow, then sealing is provided, but the seal cannot accommodate thermal deflections
Solution Approach 1:
The patent transitions from a rigid seal to a dynamic, flexible seal with axial convolutions that can adapt to thermal deflections. The flex seal dynamically adjusts its shape and position in response to thermal conditions while maintaining its backflow prevention function, resolving the contradiction between reliability and adaptability.
Solution Approach 2:
The flex seal's convoluted structure provides the flexibility needed to accommodate thermal deflections while maintaining sealing integrity. The flexible design allows the seal to deform with thermal expansion and contraction, preventing backflow without rigid constraints.
4Strength
If high fatigue limit material is used for the flex seal, then stress relief is improved, but packaging constraints in hot sections are exacerbated
Solution Approach 1:
The flex seal uses a convoluted thin-walled structure that provides high fatigue resistance through its geometric design rather than requiring excessive material volume. The axial convolutions create a flexible membrane that can withstand thermal cycling and stress while occupying minimal space within the packaging constraints of the hot section.
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 provides effective stress relief and high temperature resistance, preventing backflow and maintaining seal integrity in hot sections while accommodating thermal growth, thus enhancing engine performance and efficiency.
Implementation Method 1
a plurality of pass through features defining a purge airflow
Implementation Method 2
a heat shield immediately downstream of the first seal
Implementation Method 3
a first seal spanning from an inner diameter of the cooling air flowpath to an outer diameter of the cooling air flowpath, the first seal including at least one axial convolution
Data Source
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AI summary
A gas turbine engine includes a primary flow path (230) fluidly connecting a compressor section, a combustor section and a turbine section. A cooling air flowpath (240) is disposed radially outward of the primary flowpath (230). A first seal (210) spans from an inner diameter of the cooling air flowpath (240) to an outer diameter of the cooling air flowpath (240). The first seal (210) includes at least one axial convolution (212) and a plurality of pass through features (214) defining a purge airflow (244). A heat shield (220) is positioned immediately downstream of the first seal (210) and is configured in relation to the first seal (210) such that the purge airflow (244) enters a mixing plenum (256) defined between the heat shield (220) and the first seal (210).