Gas Turbine Flex Seal with Axial Convolutions and Heat Shield
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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 constructed from a high fatigue limit material like INCO 718 and the heat shield from a high maximum use temperature material like INCO 625, with the flex seal providing stress relief and the heat shield protecting against high temperatures, and both are mechanically fastened to the flowpath to prevent backflow and enhance sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional seals are used in hot sections, then sealing function is provided, but material limitations and packaging constraints prevent effective sealing due to thermal growth and recirculating air
Solution Approach 1:
The patent employs a flexible seal element with axial convolutions that can expand and contract axially to accommodate thermal growth between the stationary frame and rotating disk. This flexible membrane structure provides continuous sealing contact while adapting to dimensional changes caused by temperature variations, resolving the contradiction between maintaining seal integrity and adapting to thermal expansion.
Solution Approach 2:
The seal transitions from a static conventional design to a dynamic flexible structure that actively responds to thermal growth. The axial convolutions enable the seal to dynamically adjust its shape and position, maintaining effective sealing contact throughout operating temperature ranges and accommodating recirculating air conditions.
2Stability of the object's composition
If rigid seals are used to maintain seal integrity, then sealing stability is improved, but stress concentration and fatigue occur due to thermal growth and recirculating air
Solution Approach 1:
The flexible seal with axial convolutions distributes mechanical and thermal stresses along its length rather than concentrating them at fixed rigid contact points. This flexibility allows the seal to accommodate dimensional changes without developing fatigue cracks, maintaining integrity while resisting stress-induced failure.
Solution Approach 2:
The seal's physical parameters (shape, position, convolution amplitude) change dynamically in response to thermal conditions, allowing it to maintain optimal stress distribution across varying temperature ranges. This parameter adaptation prevents stress concentration and extends fatigue life.
3Temperature
If high temperature materials are used throughout the seal, then temperature resistance is improved, but fatigue limit decreases due to material properties at elevated temperatures
Solution Approach 1:
The patent employs composite construction combining flexible seal material (optimized for fatigue resistance) with heat shield materials (optimized for temperature resistance). This composite approach allows each component to be made from materials best suited for its specific functional requirements, achieving both high temperature capability and fatigue resistance.
Solution Approach 2:
The heat shield acts as an intermediary protective layer between the high-temperature environment and the flexible seal. This mediator protects the fatigue-sensitive seal material from direct thermal exposure, allowing the seal to operate in a cooler, less stressful environment while still providing sealing function in the hot section.
4Strength
If the flex seal is made from high fatigue limit material, then resistance to stress and fatigue is improved, but resistance to high temperatures decreases
Solution Approach 1:
The flexible seal is constructed from materials optimized for fatigue resistance (such as Inconel 718 or spring steel), while the heat shield uses high-temperature materials (such as Inconel 625 or ceramic coatings). This composite material selection allows each component to excel at its primary function without compromising the other.
Solution Approach 2:
The heat shield serves as a protective intermediary that shields the fatigue-optimized seal material from direct thermal exposure. This allows the seal to be made from lower temperature-rated materials that excel in fatigue resistance, while the heat shield handles the thermal protection function.
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 effectively reduces stress and thermal growth issues, preventing backflow and maintaining seal integrity in hot sections by using materials optimized for fatigue and temperature resistance, thereby improving sealing efficiency and engine performance.
Implementation Method 1
effectively sealing interfaces between static frames and flowpath fairings due to recirculating air and thermal growth
Implementation Method 2
the flex seal including at least one axial convolution... the flex seal providing stress relief
Implementation Method 3
the purge airflow enters a mixing plenum defined between the heat shield and the first seal... preventing backflow
Implementation Method 4
the heat shield being configured in relation to the first seal such that the purge airflow enters a mixing plenum defined between the heat shield and the first seal
Implementation Method 5
the purge airflow enters a mixing plenum... passing an airflow through the flex seal into the purge air plenum
Data Source
AI summary
A gas turbine engine includes a primary flow path fluidly connecting a compressor section, a combustor section and a turbine section. A cooling air flowpath is disposed radially outward of the primary flowpath. A first seal spans from an inner diameter of the cooling air flowpath to an outer diameter of the cooling air flowpath. The first seal includes at least one axial convolution and a plurality of pass through features defining a purge airflow. A heat shield is positioned immediately downstream of the first seal and is configured in relation to the first seal such that the purge airflow enters a mixing plenum defined between the heat shield and the first seal.