Hollow CMC Blade Outer Air Seal Segment Design
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Solution Overview
Problem
Existing ceramic matrix composite (CMC) blade outer air seal segments for gas turbine engines face challenges in ensuring efficient sealing and thermal stress management due to complex manufacturing requirements and thermal gradient issues, which affect the durability and stability of the seals.
Innovation Solution
The design incorporates a ceramic matrix composite blade outer air seal segment with a rectangular slot and a mating feature that forms a hook to engage with adjacent segments, allowing for radial installation and increased contact area with support structures, reducing thermal gradient stresses and simplifying manufacturing through a hollow structure with access slots and retaining clips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid ceramic matrix composite structure is used for the blade outer air seal segment, then the sealing performance and thermal resistance are improved, but the thermal gradient stresses increase and manufacturing complexity increases
Solution Approach 1:
The patent applies a hollow nested structure where an inner cavity is formed within the ceramic matrix composite seal segment. This nested configuration reduces the overall material volume, thereby reducing thermal gradient stresses while maintaining the external sealing surface integrity. The hollow structure allows thermal stress relief without compromising the sealing function.
Solution Approach 2:
The seal segment is divided into functional zones: an outer wall for sealing, a base portion for support engagement, and an inner cavity for stress relief. This segmentation allows each zone to be optimized independently - the outer wall maintains sealing performance while the hollow interior reduces thermal stresses.
2Reliability
If a complex solid structure is used for the air seal segment, then the sealing performance is improved, but the manufacturing difficulty increases
Solution Approach 1:
The hollow inner cavity is formed during the manufacturing process itself, rather than requiring post-manufacturing operations. The CMC structure is molded or formed with the cavity already present, eliminating the need for complex drilling, machining, or assembly operations that would be required for a solid structure.
Solution Approach 2:
Instead of starting with a solid structure and removing material to create cavities (which would be complex), the invention inverts the approach by directly forming the hollow structure during manufacturing. This reverses the traditional subtractive manufacturing logic and simplifies the process.
3Stress or pressure
If the outer wall width is reduced to lower thermal mass, then the thermal gradient stresses are reduced, but the structural strength decreases
Solution Approach 1:
The patent utilizes ceramic matrix composite materials that provide high strength-to-weight ratio and excellent thermal resistance. The CMC material allows the outer wall to be thinner (reducing thermal mass and gradients) while maintaining sufficient structural strength through the composite's inherent material properties.
Solution Approach 2:
The base portion is designed with greater width and material volume compared to the outer wall, concentrating structural strength where needed for support engagement while keeping the outer wall thin for thermal management. This local differentiation of material distribution optimizes both strength and thermal performance.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A blade outer air seal (106) includes a base portion (124) that extends between a first circumferential side (CI) and a second circumferential side (C2). A first wall (120) is circumferentially spaced from a second wall (122). The first and second walls (120, 122) extend outward from the base portion (124) and are connected by an outer wall (126) to define a passage that extends in a generally axial direction along the base portion (124).