Variable Blade Outer Air Seal Clearance Control
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Solution Overview
Problem
Current clearance control systems for gas turbine engines, both active and passive, fail to effectively maintain optimal clearance between blade outer air seals and turbine blades across the entire engine operating envelope, leading to performance issues, especially in high-pressure turbine blades, which affects engine efficiency and longevity.
Innovation Solution
A modulated blade outer air seal system with an actuator and control system that adjusts the gap between blade tips and the engine case based on real-time temperature and flight condition measurements, using a combination of mechanical and thermal controls to actively manage clearance and reduce wear on components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If passive clearance control is used to continuously limit outer case expansion, then clearance is held to a minimum, but the system cannot move the BOAS away from the blades and maintain clearance at a high rate across the entire engine envelope
Solution Approach 1:
The patent applies dynamics by making the BOAS movable rather than fixed. The BOAS is coupled to an actuator that can actively adjust its position along the blade tip, enabling the system to adapt clearance dynamically across different operating conditions. This resolves the contradiction by allowing the system to maintain precision while achieving adaptability across the entire engine envelope.
Solution Approach 2:
The system uses self-service by allowing the BOAS to be positioned by the actuator in response to real-time operating conditions. The control system automatically adjusts the BOAS position based on sensor feedback, eliminating the need for external manual intervention and enabling the system to maintain optimal clearance autonomously across varying operating envelopes.
2Manufacturing precision
If active clearance control impinges air on the engine case to shrink it, then clearance is reduced at predetermined times, but the system cannot maintain clearance at a high rate across the entire engine envelope
Solution Approach 1:
The patent replaces the thermal-mechanical approach of active clearance control (impinging air to shrink the case) with a direct mechanical actuation system. The actuator mechanically positions the BOAS along the blade tip, providing faster and more precise clearance adjustment. This substitution enables the system to maintain high adjustment rates across the entire engine envelope while preserving clearance control precision.
3Adaptability or versatility
If a variable BOAS arrangement with actuator is implemented, then clearance can be actively controlled across the entire engine envelope, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the actuator and control system to handle multiple functions: positioning the BOAS, sensing operating conditions, and adjusting clearance across the entire engine envelope. This multi-functional approach reduces overall system complexity compared to having separate systems for each function, while maintaining high adaptability.
Solution Approach 2:
The system uses feedback by incorporating sensors that monitor operating conditions and feed this information to the control system, which then adjusts the BOAS position accordingly. This closed-loop feedback mechanism enables the complex variable BOAS arrangement to automatically maintain optimal clearance across the entire engine envelope, managing complexity through intelligent control rather than mechanical complexity.
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 system maintains optimal performance and reduces wear on turbine components by actively controlling blade tip gaps across the entire flight envelope, improving engine efficiency and extending service life while simplifying design and reducing costs.
Implementation Method 1
The clearance control systems currently utilized, either passive or active, are not capable of moving the BOAS away from the blades and maintaining clearance at a high rate or across the entire engine envelope
Implementation Method 2
one such system continuously impinges cooling air on the outer engine case in proximity to the rotor blades to limit the rate of expansion of the outer case subjected to elevated temperatures
Data Source
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AI summary
A system for a turbofan has a variable outer air seal, an actuator coupled to the variable outer air seal, a sensor positioned inside the turbofan for sensing an engine parameter, and a flight controller connected to the turbofan for receiving the parameter from the sensor. The flight controller directs the actuator to regulate the position of the actuator based on the flight condition resulting form the received parameter.