Frangible Gas Turbine Airfoil Leading Edge Sheath Design
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Solution Overview
Problem
Airfoils in gas turbine engines face challenges with extreme loading events, such as bird strikes, leading to uncontrolled failure modes that increase weight and reduce efficiency, as existing frangible structures are costly and do not adequately address issues of fan rotor unbalance.
Innovation Solution
The airfoil design incorporates a leading edge sheath with a flange and base that define a frangible line, allowing for a controlled failure mode by reducing bending stiffness in the frangible portion, enabling it to break off or deform during failure events, thus mitigating load transfer to the surrounding casing and reducing unbalance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If known fan cases include frangible structures such as honeycombs or trench-filler material to mitigate load transfer, then load transfer to fan case is reduced, but cost increases and fan case weight increases
Solution Approach 1:
The airfoil is segmented into a frangible portion and a non-frangible portion, allowing the frangible portion to break away during extreme loading events while the non-frangible portion remains intact. This segmentation eliminates the need for heavy frangible structures in the fan case while still achieving load mitigation.
Solution Approach 2:
The airfoil has different structural properties at different locations: the frangible portion has reduced bending stiffness to enable controlled breakage, while the non-frangible portion maintains full structural integrity. This local differentiation allows load transfer reduction without adding overall weight to the fan case.
2Reliability
If fan blade is made robust to withstand extreme loading events, then reliability is improved, but weight increases and efficiency reduces
Solution Approach 1:
The fan blade is divided into frangible and non-frangible portions, allowing the blade to have sufficient strength where needed while being lightweight overall. The frangible portion is designed to break away during extreme events, preventing catastrophic failure while minimizing weight.
Solution Approach 2:
The bending stiffness parameter is changed locally in the frangible portion to enable controlled breakage. By adjusting the stiffness parameter in specific regions rather than making the entire blade robust, the blade achieves necessary reliability without excessive weight.
3Force
If frangible structures are added to fan case to mitigate load transfer, then load transfer is reduced, but device complexity increases
Solution Approach 1:
The frangible functionality is extracted from the fan case structure and transferred to the airfoil itself. Instead of adding complex frangible structures to the fan case, the airfoil is designed with inherent frangible characteristics, simplifying the overall device complexity.
4Ease of manufacture
If conventional airfoil design is used without frangible features, then manufacturing simplicity is maintained, but uncontrolled failure mode increases risk and cost
Solution Approach 1:
The airfoil is segmented into frangible and non-frangible portions that can be manufactured using standard processes. The segmentation is achieved through design features like varying thickness or material properties rather than complex assembly, maintaining manufacturing simplicity while enabling controlled failure modes.
Data Source
AI summary
An airfoil defining a span extending between a root and a tip and a chord at each point along the span extending between a leading edge and a trailing edge. The airfoil includes a leading edge sheath coupled to the leading edge of the airfoil. The leading edge sheath includes a flange extending from a frangible line toward the tip along the span and defining a first width along the chord at each point along the span S. The leading edge sheath further includes a base extending from the frangible line at least partially along the span to the root and defining a second width along the chord at a point along the span of the frangible line such that the second width is greater than the first width.