Segmented BOAS Air Seal with Anti-Rotation Tabs for Gas Turbine Engines
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Solution Overview
Problem
Gas turbine engines, particularly turboshaft engines, face challenges in maintaining efficient tip clearance due to erosion of abradable coatings in dusty environments, leading to increased leakage and reduced performance, especially in small engines where thermal expansion complicates the design of full-hoop blade outer air seal rings.
Innovation Solution
The implementation of a full-hoop vane ring with anti-rotation tabs and BOAS segments featuring aft engagement features and anti-rotation tabs, which allows for thermal expansion independence while maintaining radial fixity, combined with active clearance control systems to minimize tip clearance and leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a full-hoop BOAS ring is used to eliminate segmentation gaps and reduce leakage, then leakage is reduced, but thermal expansion causes the BOAS ring to grow in radius independently, increasing tip clearance
Solution Approach 1:
The BOAS ring is divided into multiple segments that can expand and contract independently in the radial direction while maintaining circumferential continuity. This segmentation allows each segment to accommodate thermal expansion without causing the entire ring to grow in radius, thus reducing leakage while maintaining tip clearance.
Solution Approach 2:
The BOAS ring incorporates active clearance control mechanisms that dynamically adjust the radial position of the segments in response to thermal conditions. This dynamic adjustment allows the system to optimize both leakage reduction and tip clearance maintenance under varying thermal expansion conditions.
2Stability of the object's composition
If the BOAS ring is designed to be thermally independent to accommodate expansion, then thermal expansion is managed, but active clearance control systems cannot be used
Solution Approach 1:
The BOAS ring is segmented to allow independent thermal expansion of each segment while maintaining overall structural integrity. This segmentation enables the ring to be thermally independent without precluding active clearance control, as the segments can still be actuated to adjust tip clearance dynamically.
Solution Approach 2:
The segmented structure acts as an intermediary between thermal expansion forces and the active clearance control system. Each segment can expand thermally while still being subject to active control forces, allowing both thermal independence and active clearance control to function simultaneously.
3Stability of the object's composition
If segmented BOAS are used to allow thermal expansion, then thermal independence is achieved, but leakage increases due to gaps between segments
Solution Approach 1:
The segments are connected by flexible seals that maintain circumferential continuity while allowing radial expansion. These flexible sealing elements prevent leakage through the segmentation gaps while accommodating thermal expansion, thus achieving both thermal independence and leakage reduction.
Solution Approach 2:
The sealing system incorporates dynamic elements that adapt to thermal expansion conditions. The flexible seals maintain contact between segments during expansion, preventing leakage while allowing the segments to move independently thermally.
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 enhances the stability and efficiency of gas turbine engines by reducing leakage and accommodating thermal expansion, thereby improving power and low rpm efficiency while maintaining a tight tip clearance.
Implementation Method 1
The rubbing wears the abradable material such that the blade tips then have a reduced tip clearance relative to the idealized geometry
Implementation Method 2
erosion resistant abradable blade outer air seal
Implementation Method 3
The BOAS may be subjected to relatively intense temperatures during gas turbine engine operation
Data Source
AI summary
An interface for a gas turbine engine. The interface includes a full-hoop vane ring around the engine axis, the full-hoop vane ring comprises a forward vane rail with a vane ring forward contact surface and a vane ring anti-rotation tab, the vane ring anti-rotation tab engaged with the anti-rotation case slot; and a multiple of BOAS segments around the engine axis, each of the multiple of BOAS segments comprise a BOAS aft engagement feature and a BOAS aft contact surface, the BOAS aft engagement feature engaged with the outer case and the anti-rotation case slot, the BOAS aft contact surface abuts the vane ring forward contact surface.