Blade Outer Air Seal Relief Gap Thermal Expansion
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Solution Overview
Problem
Gas turbine engines face inefficiencies due to excessive clearances between blade tips and outer air seals, leading to aerodynamic losses and stress on the seals, especially in high-temperature environments, where thermal gradients cause uneven expansion and increased clearances.
Innovation Solution
A blade outer air seal (BOAS) with a relief gap within the seal body allows a portion of the radially inward side to expand into the gap when heated, reducing stress and maintaining optimal clearance between the seal and blade tips, connected to the engine case through hooks and optionally featuring a cooling fluid compartment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the clearance between blade tips and outer air seals is reduced to improve aerodynamic efficiency, then tip leakage losses are reduced, but the risk of abrasion and rubbing between components increases
Solution Approach 1:
The air seal is designed with a compliant structure that can dynamically adjust its position and shape in response to thermal expansion and mechanical loads. The seal includes a radially inwardly extending portion with relief gaps that allow the seal to flex and accommodate blade tip movements, maintaining optimal clearance without rigid contact that would cause abrasion.
Solution Approach 2:
The relief gaps in the air seal structure allow for controlled dimensional changes in response to temperature variations. As the seal heats up during operation, the gaps enable the seal material to expand radially inward without generating excessive stress, thereby maintaining the designed clearance geometry under thermal loads and preventing both rubbing and excessive leakage.
2Reliability
If the clearance gap is oversized to avoid abrasion between blade tips and air seals, then component reliability is improved, but aerodynamic efficiency and engine cycle efficiency deteriorate
Solution Approach 1:
The air seal transitions from a rigid fixed-gap design to a dynamic compliant structure. The relief gaps enable the seal to adapt its effective clearance in real-time based on operating conditions, maintaining small clearances for efficiency while accommodating blade movements that would otherwise cause rubbing, thus achieving both reliability and productivity.
3Temperature
If the blade outer air seal is subjected to high thermal loads, then the seal may expand and increase clearances reducing efficiency, but the seal structure must remain stable
Solution Approach 1:
The relief gaps are specifically designed to accommodate thermal expansion of the air seal structure. When the seal is heated during engine operation, the gaps allow the seal material to expand radially inward without generating destructive thermal stress, thereby maintaining the intended clearance geometry and preventing both structural failure and excessive clearance growth that would reduce efficiency.
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 solution reduces stress on the seal and maintains optimal clearance, enhancing the efficiency of the gas turbine engine by allowing thermal expansion within the seal, thus minimizing aerodynamic losses and maintaining performance under varying thermal conditions.
Implementation Method 1
a relief gap within the seal body to allow a portion of the radially inward side to expand into the relief gap when the seal body is heated
Data Source
AI summary
A blade outer air seal (BOAS) is provided. The BOAS comprising: a seal body having a forward side, an aft side opposite the forward side, a radially inward side, and a radially outward side opposite the radially inward side; and a relief gap within the seal body to allow a portion of the radially inward side to expand into the relief gap when the seal body is heated.