Active Tip Clearance Control with Isolated Bypass Air Venting
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Solution Overview
Problem
In turbofan gas turbine engines, the limited pressure differential available for active tip clearance control (ATCC) systems can result in marginal driving pressure, which may degrade engine performance, especially when a scoop is used to enhance pressure, impacting bypass duct performance, or lead to performance degradation if the core compartment is vented to atmospheric pressure.
Innovation Solution
An ATCC system that includes a vent passage for the bypass air flow, allowing it to be discharged into the atmosphere while maintaining the core compartment pressurized, eliminating the need for a scoop by creating a sealed annular cavity with a pressure differential that enables effective impingement cooling without compromising thrust recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a scoop is used in the bypass air duct to create dynamic pressure head, then the pressure differential for ATCC is improved, but bypass duct performance is degraded
Solution Approach 1:
The invention extracts the scooping function from the bypass air duct by providing a separate inlet passage that opens into the core compartment. This allows the ATCC system to obtain pressurized air without creating obstacles in the bypass duct, thereby eliminating the negative impact on bypass duct performance while still achieving the required pressure differential for active tip clearance control
Solution Approach 2:
The core compartment serves as an intermediary space that receives pressurized air from the bypass air duct through a dedicated inlet passage. This intermediary approach allows the system to transfer pressurized air to the ATCC apparatus without directly obstructing the bypass duct flow, resolving the contradiction between achieving sufficient pressure differential and maintaining bypass duct performance
2Device complexity
If the core compartment is vented to atmospheric pressure, then ATCC can function without a scoop, but engine performance is degraded due to loss of bypass air thrust recovery
Solution Approach 1:
The invention applies local quality by maintaining different pressure conditions in different regions: the core compartment remains pressurized to enable thrust recovery, while the ATCC apparatus receives pressurized air through a dedicated passage. This localized approach allows the system to achieve simplified ATCC operation without venting the entire core compartment, thereby avoiding engine performance degradation
Solution Approach 2:
The system segments the air flow paths by providing a separate inlet passage for the ATCC apparatus within the core compartment. This segmentation allows bypass air to be directed to the ATCC system without being vented to atmosphere, maintaining the pressurized environment needed for thrust recovery while still enabling simplified ATCC 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
This solution maintains engine performance by providing a sufficient pressure differential for ATCC without degrading bypass duct performance and allows for efficient thrust recovery, as the majority of bypass air is still used for cooling engine components within the core compartment.
Implementation Method 1
The vent passage (44) is provided to the ATCC apparatus (38) and is in fluid communication with the atmosphere. The ATCC apparatus (38) is sealed to prevent the second portion (42) of the bypass air flow passing through the ATCC apparatus (38), from mixing with the first portion (34) of the bypass air flow
Implementation Method 2
creating a sealed annular cavity with a pressure differential that enables effective impingement cooling
Data Source
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AI summary
An active tip clearance control (ATCC) apparatus (38) of an aircraft gas turbine engine is situated within a pressurized core case (13) of the engine. First and second portions (34,42) of bypass air flow passing through a compressed core compartment (30) and the ATCC apparatus (38), are isolated from one another in order to improve both the ATCC performance and bypass air duct performance.