CMC Nozzle Strut Load Transfer and Thermal Expansion
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Solution Overview
Problem
Ceramic matrix composite (CMC) nozzles in gas turbine engines face durability challenges due to stress concentrations from differential thermal expansion and mechanical properties, leading to potential failure under high temperature and pressure conditions.
Innovation Solution
A nozzle assembly featuring a low coefficient of thermal expansion material with a metallic strut that transfers load between the nozzle fairing and support rings, allowing for differential thermal growth and minimizing stress concentrations, while also enabling internal airflow for cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CMC materials are used for nozzle components to operate at higher temperatures, then engine efficiency is improved, but stress concentrations develop due to differential thermal expansion with metallic supports leading to potential failure
Solution Approach 1:
A metallic strut is introduced as an intermediary component between the CMC nozzle and the engine structure. The strut serves as a mediator that accommodates differential thermal expansion between the CMC material and metallic supports, preventing stress concentrations while allowing the nozzle to operate at higher temperatures
Solution Approach 2:
The design changes the structural configuration by introducing a strut that can independently expand and contract, effectively decoupling the thermal expansion parameters of the CMC nozzle from the metallic support structure. This allows each component to operate with its optimal thermal expansion characteristics
2Strength
If load is transferred from CMC nozzle to support rings through direct attachment, then structural support is provided, but high stresses develop at the interface between vanes and bands creating durability challenges
Solution Approach 1:
The metallic strut acts as an intermediary load transfer path, carrying forces between the CMC nozzle and support rings without creating high stress concentrations at the vulnerable interfaces between vanes and bands. The strut distributes loads more evenly throughout the structure
Solution Approach 2:
The nozzle structure is segmented into distinct components (nozzle body, struts, support rings) that can independently manage different aspects of the mechanical loads, allowing each component to be optimized for its specific function while reducing stress concentrations at interfaces
3Temperature
If CMC nozzle is restrained and cooled on one surface during operation, then thermal management is achieved, but stress concentrations develop leading to failure of the segment
Solution Approach 1:
The metallic strut serves as a thermal and mechanical intermediary that allows one-sided cooling of the CMC nozzle without creating detrimental stress concentrations. The strut's different thermal expansion characteristics compared to CMC materials enable it to accommodate the differential movement caused by asymmetric cooling
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 supports CMC nozzles by distributing loads and accommodating thermal expansion differences, enhancing durability and reducing stress concentrations, thereby improving the operational reliability of gas turbine engines.
Implementation Method 1
CMC materials have a coefficient of thermal expansion which differs significantly from metal alloys used as restraining supports or hangers for CMC type materials. Therefore, if a CMC component is restrained and cooled on one surface during operation, stress concentrations can develop leading to failure of the segment.
Implementation Method 2
These components operate in an extremely high temperature environment, and must be cooled by air flow to ensure adequate service life.
Data Source
AI summary
A nozzle assembly is provided which is, in part, formed of a low coefficient of thermal expansion material. The assembly includes a nozzle fairing formed of the low coefficient of thermal expansion material and includes a metallic strut extending radially through the nozzle fairing. Load is transferred from the nozzle fairing to a static structure in either of two ways: first, the strut may receive the load directly and/or second, load may be transferred from the nozzle fairing to at least one of the inner and outer support rings. Further, the nozzle fairing and strut may allow for internal airflow for cooling.