Composite Airfoil Leading Edge Stress Mitigation
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Solution Overview
Problem
Gas turbine engine airfoils experience high stresses at the leading edge due to pressure differentials, limiting the use of materials with favorable thermal performance properties like ceramic composites.
Innovation Solution
The airfoil assembly features an outer wall with a smaller leading edge radius and an inner wall with a larger radius, creating a cavity filled with ceramic matrix composite material to distribute stress and accommodate pressure differentials, while the trailing edge also includes spaced plies of material for additional support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a small leading edge radius is used to maintain aerodynamic shape, then the aerodynamic performance is improved, but large stresses are generated at the leading edge
Solution Approach 1:
The airfoil is segmented into an outer wall and an inner wall, creating a double-walled structure with a cavity between them. This segmentation allows the leading edge to have a small external radius for aerodynamic performance while the internal structure can have a larger radius to reduce stress concentration.
Solution Approach 2:
The invention uses ceramic matrix composite materials for both the outer and inner walls, combining the thermal performance benefits of ceramics with the stress-mitigation capabilities of the double-walled composite structure. The composite nature allows for tailored mechanical properties that balance aerodynamic and structural requirements.
2Temperature
If ceramic matrix composite materials are used to achieve favorable thermal performance, then thermal resistance is improved, but large stresses at the leading edge prevent their use
Solution Approach 1:
The double-walled structure segments the airfoil into outer and inner walls with a cavity between them. This segmentation creates a stress-mitigation feature that reduces stress concentrations at the leading edge, enabling the use of ceramic matrix composites that would otherwise be too stress-sensitive.
Solution Approach 2:
The invention employs ceramic matrix composite materials for both walls, leveraging their excellent thermal resistance properties while the composite structure itself provides enhanced stress resistance through the stress-mitigation geometry.
3Power
If pressure differential is increased to improve engine performance, then power output is improved, but stress at the leading edge increases
Solution Approach 1:
The segmented double-walled structure with cavity creates a stress-mitigation feature that distributes and reduces stress concentrations at the leading edge, allowing the airfoil to withstand higher pressure differentials that enable improved engine power output.
4Ease of manufacture
If a single-walled airfoil structure is used to simplify manufacturing, then manufacturing complexity is reduced, but stress concentrations cannot be mitigated
Solution Approach 1:
The airfoil is divided into an outer wall and an inner wall with a cavity between them. This segmentation, while adding structural complexity, is designed to be manufacturable using ceramic matrix composite fabrication techniques, and provides critical stress-mitigation functionality.
Data Source
AI summary
A vane assembly within a mid-turbine frame of a gas turbine engine includes an airfoil that extends between an outer platform and an inner platform. The airfoil includes an outer wall defining a leading edge of a first radius. An inner wall of the airfoil defines an inner cavity including a forward portion proximate the leading edge defining a second radius different than the first radius.