Segmented Spline Blade Outer Air Seal for Turbine Tip Clearance
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Solution Overview
Problem
Gas turbine engines face challenges in maintaining a tight tip clearance between blade tips and the outer radial flow path boundary due to thermal expansion, leading to increased leakage and reduced efficiency, especially in smaller engines where the tip clearance is more significant relative to the flow path.
Innovation Solution
A blade outer air seal (BOAS) with a segmented spline extending from a full hoop seal ring body, which selectively abuts a pad on the engine casing to provide a non-linear thermal response, controlling purge airflow and thermal expansion to match the blade design, thereby reducing tip clearance and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a full-hoop ring BOAS is used to minimize tip clearance leakage, then leakage is reduced, but the BOAS grows more in radius than the blades making tight tip clearance design more complex
Solution Approach 1:
The BOAS is divided into multiple axially-spaced segments rather than being a continuous full-hoop ring. Each segment can independently control purge airflow and thermal expansion, reducing the overall complexity of designing tight tip clearance while maintaining effective leakage reduction through coordinated operation of the segments
2Productivity
If the clearance between blade tips and outer radial flow path boundary is made small to increase efficiency, then efficiency improves, but thermal expansion causes increased leakage and reduced efficiency
Solution Approach 1:
The BOAS segments are designed to dynamically adjust their position and purge airflow in response to thermal conditions. As thermal expansion occurs, the segments can move axially and adjust purge flow rates to maintain optimal tip clearance and prevent excessive leakage, allowing the system to adapt to changing thermal states while preserving efficiency
Solution Approach 2:
The system changes operational parameters including purge airflow rate, segment axial position, and thermal mass distribution to compensate for thermal expansion. By adjusting these parameters dynamically, the BOAS maintains effective tip clearance control despite temperature variations, preventing leakage increase and preserving efficiency
3Length of moving object
If abradable material is used to reduce tip clearance through rubbing wear, then tip clearance is reduced, but the blade tips must rub against the BOAS causing material wear
Solution Approach 1:
The BOAS segments incorporate abradable material as a protective cushion layer that can withstand controlled rubbing during startup and transient conditions. This beforehand cushioning allows the blade tips to safely contact the BOAS during normal operation to establish proper tip clearance, while the wear is contained and predictable, occurring primarily during controlled phases rather than continuous operation
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 non-linear thermal response system effectively reduces tip clearance, enhancing turbine performance and reducing specific fuel consumption by controlling thermal growth and contraction of the BOAS, resulting in improved efficiency and power output.
Implementation Method 1
the segmented spline selectively abuts an engine casing to provide a non-linear thermal response of the blade outer air seal (BOAS) with respect to the turbine rotor
Implementation Method 2
The segmented spline controls a purge airflow between the radially outer face and an engine casing
Implementation Method 3
a thermal barrier coating applied to at least a portion of a radially inner face of the seal
Data Source
AI summary
A blade outer air seal (BOAS) for a gas turbine engine includes a seal ring body having a radially inner face and a radially outer face that axially extend between a leading edge portion and a trailing edge portion and a segmented spline that extends from the radially outer face of the seal ring body, the seal secured to the radially inner face of the seal ring body.