Ceramic Matrix Composite Blade Outer Air Seal Stress Management
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Solution Overview
Problem
Existing blade outer air seal assemblies in gas turbine engines face challenges in ensuring effective sealing and stress management due to thermal expansion and mechanical loading, particularly when using ceramic matrix composite materials.
Innovation Solution
A blade outer air seal assembly featuring ceramic segments with a metallic carrier, where the carrier has slots and pins for secure attachment, and incorporates a rope seal and feather seal for enhanced sealing, with the pins being press-fit into countersunk holes to manage stress and thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic matrix composite materials are used for blade outer air seals, then high temperature resistance and durability are improved, but thermal expansion and mechanical loading cause stress management issues
Solution Approach 1:
The air seal is divided into multiple segments that can expand and contract independently, allowing each segment to accommodate thermal expansion without generating excessive stress. The segments are connected through a flexible mounting structure that permits thermal movement while maintaining sealing contact.
Solution Approach 2:
The mounting parameters of the air seal segments are designed to change with temperature, allowing the segments to move radially and axially in response to thermal expansion. This includes provisions for thermal growth gaps and flexible mounting arrangements that adapt to temperature variations.
2Temperature
If ceramic matrix composite materials are used for blade outer air seals, then high temperature resistance is improved, but mechanical loading increases
Solution Approach 1:
A metallic carrier or mounting structure serves as an intermediary between the ceramic air seal segments and the engine structure. This intermediary absorbs and distributes mechanical loads, protecting the ceramic material from excessive stress while allowing the ceramic to maintain its high-temperature sealing function.
Solution Approach 2:
The air seal assembly uses a composite structure combining ceramic matrix composite segments for high-temperature resistance with a metallic carrier or mounting structure for mechanical strength. This hybrid approach allows each material to perform its optimal function while reducing overall mechanical loading on the ceramic portions.
3Reliability
If secure attachment is provided for ceramic segments, then sealing reliability is improved, but stress concentration increases
Solution Approach 1:
The attachment system is segmented into multiple attachment points distributed around the air seal segments. This distributes the attachment forces across multiple locations, preventing stress concentration at any single attachment point while maintaining secure attachment of the ceramic segments.
Solution Approach 2:
The attachment structure provides different local properties at different locations - rigid attachment where structural support is needed and flexible or compliant attachment where thermal movement is expected. This localized differentiation allows secure attachment without uniform stress concentration.
Data Source
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AI summary
A blade outer air seal assembly (104) includes a carrier (112) that has a slot (114; 115; 116; 117) and a hole (140) that extends into the slot. A blade outer air seal (106) has a plurality of segments (105) that extend circumferentially about an axis and mounted in the carrier (112). At least one of the plurality of segments (105) has a base portion (124) and a first wall (120) that extends axially and radially outwardly from the base portion (124). The first wall (120) has an aperture (130; 131). A pin (160) extends through the hole and the aperture.