Resilient Mounting for Low-Ductility Turbine Shroud
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Solution Overview
Problem
Low-ductility materials like ceramic matrix composites (CMCs) used in gas turbine engine shrouds experience differential thermal expansion issues, leading to overconstraint, overloads, and loss of preload due to their different thermal expansion coefficients compared to metallic hardware, necessitating a resilient mounting solution.
Innovation Solution
A resilient mounting apparatus using spring elements, such as wave springs and W-seals, between low-ductility turbine shroud segments and metallic structures to maintain axial position and accommodate thermal expansion, ensuring proper sealing and preload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rigid metallic mounting structures are used to securely position CMC shroud segments, then the shroud segments are firmly held in position, but differential thermal expansion causes overconstraint, overloads, and loss of preload
Solution Approach 1:
The mounting structure changes from rigid to compliant by introducing spring elements that can deflect axially. This parameter change allows the structure to accommodate thermal expansion while maintaining secure positioning and preventing overconstraint and preload loss.
Solution Approach 2:
Spring elements are introduced as intermediary components between the rigid metallic mounting structure and the CMC shroud segments. These intermediaries absorb thermal expansion differences through elastic deformation, preventing direct transmission of thermal stresses to the shroud segments.
2Manufacturing precision
If rigid mounting structures are used to maintain axial position, then positioning is precise, but thermal expansion differences cause overconstraint and overloads
Solution Approach 1:
The mounting structure transitions from a static rigid connection to a dynamic compliant connection using spring elements. These springs can deflect axially to accommodate thermal expansion while maintaining precise positioning, converting the static constraint into a dynamic adaptive system.
Solution Approach 2:
The structural stiffness parameter is changed by introducing compliant spring elements. This allows the mounting structure to maintain positioning accuracy while changing from a rigid constraint to a flexible accommodation of thermal dimensional changes.
3Device complexity
If friction-based axial positioning is used, then simple mounting is achieved, but reliance on friction is insufficient to prevent preload loss under thermal loading
Solution Approach 1:
The friction-based mechanical positioning system is replaced with a spring-based elastic constraint system. The springs provide active axial constraint forces that are more reliable than friction, maintaining preload under thermal loading while adding minimal complexity to the mounting structure.
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 effectively maintains secure positioning and sealing of low-ductility shroud segments despite thermal expansion differences, preventing overloads and preload loss, and reduces reliance on friction for axial positioning.
Implementation Method 1
a first spring element disposed between the flowpath component and the stationary structure which resiliently urges the flowpath in a first axial direction; and a second spring element disposed between the flowpath component and the stationary structure which resiliently urges the flowpath component in a second axial direction
Implementation Method 2
a spring element disposed between the flowpath component and the stationary structure which resilient urges the flowpath component in the first direction against the bearing surface
Data Source
AI summary
A turbine flowpath apparatus for a gas turbine engine includes: a flowpath component exposed at least partially to a primary combustion gas flowpath of the engine, the flowpath component comprising low-ductility material; a metallic annular stationary structure surrounding the flowpath component, including a bearing surface which bears against the flowpath component, so as to restrain the flowpath component from axial movement in a first direction; and a spring element disposed between the flowpath component and the stationary structure which resilient urges the flowpath component in the first direction against the bearing surface.