Variable Temperature Blade Outer Air Seal Clearance Control
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Solution Overview
Problem
In gas turbine engines, the differential thermal expansion of blades, blade outer air seals, and supporting structures leads to varying tip clearances, which can result in reduced efficiency due to leakage and potential rubbing issues, as existing clearance control systems struggle to maintain optimal clearances across different operational conditions.
Innovation Solution
A clearance control system utilizing a heat exchanger to deliver air at varying temperatures to the blade outer air seal, allowing it to move radially to maintain desired clearances, with hot air used during engine acceleration to expand the seal outwardly and cold air during cruise to shrink it inwardly, thereby controlling tip clearance effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the blade outer air seal is spaced from the blade tip by a fixed clearance, then the structure is simple, but the tip clearance cannot be maintained optimal under varying temperature and operational conditions
Solution Approach 1:
The patent applies dynamics by making the blade outer air seal position variable rather than fixed. The seal is allowed to move radially inward or outward in response to temperature changes and operational conditions, enabling dynamic adaptation to maintain optimal clearance without requiring a complex active control system.
Solution Approach 2:
The patent utilizes parameter changes by allowing the radial position of the blade outer air seal to vary based on temperature and operational parameters. By changing the seal position parameter dynamically, the system maintains optimal clearance across different operating conditions while keeping the control mechanism relatively simple.
2Ease of operation
If the blade outer air seal is allowed to move freely with temperature changes, then the structure is simple, but the clearance becomes uncontrolled and may cause rubbing or leakage
Solution Approach 1:
The patent applies self-service by designing the blade outer air seal to automatically adjust its position in response to temperature changes and operational conditions. The seal moves radially inward or outward based on thermal expansion and contraction, providing self-regulating clearance control without requiring external active control systems.
Solution Approach 2:
The patent replaces complex mechanical control systems with a thermally-driven passive control mechanism. Instead of using actuators or control mechanisms to adjust clearance, the system relies on thermal expansion and contraction of the seal and supporting structures to automatically maintain optimal clearance.
3Productivity
If the tip clearance is reduced to improve engine efficiency, then the efficiency increases, but the risk of rubbing and leakage increases
Solution Approach 1:
The patent applies dynamics by making the blade outer air seal position variable rather than fixed. The seal is allowed to move radially inward or outward in response to temperature changes and operational conditions, enabling dynamic adaptation to maintain optimal clearance without requiring a complex active control system.
Solution Approach 2:
The patent utilizes parameter changes by allowing the radial position of the blade outer air seal to vary based on temperature and operational parameters. By changing the seal position parameter dynamically, the system maintains optimal clearance across different operating conditions while keeping the control mechanism relatively simple.
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 solution effectively reduces tip clearance, enhances engine efficiency, and prolongs the life of the blade outer air seal by actively managing thermal growth and maintaining optimal clearance conditions across different flight conditions.
Implementation Method 1
the blade outer air seal, and structure that support the BOAS are different sizes and/or are formed of different materials, they respond to temperature changes in different manners. As these structures expand at different rates during heating, the tip clearance may be reduced
Implementation Method 2
air supplied at the second temperature directly cools the carrier to move the blade outer air seal radially inwardly in the second direction
Data Source
AI summary
A clearance control system for a gas turbine engine comprises a blade outer air seal mounted on a carrier. At least one blade is rotatable about an engine axis. The blade outer air seal is spaced radially outwardly from a tip of the blade by a clearance. A heat exchanger is configured to deliver air at a first temperature to the blade outer air seal at a first operating condition to allow the blade outer air seal to move in a first direction to maintain a desired clearance, and configured to deliver air at a second temperature to the blade outer air seal at a second operating condition to allow the blade outer air seal to move in a second direction to maintain a desired clearance, and wherein the second temperature is less than the first temperature. A gas turbine engine and a method of controlling tip clearance in a gas turbine engine are also disclosed.