CMC Airfoil Rib with Thermal Conduction for Stress Reduction
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Solution Overview
Problem
Ceramic matrix composite (CMC) airfoils in gas turbine engines face challenges with thermal gradients and stress due to low thermal conductivity, which can lead to distress from thermally induced stresses, and traditional cooling methods may exacerbate these issues.
Innovation Solution
An airfoil design featuring a rib with a thermal conductance element between forward and aft ceramic matrix composite skins, where the thermal conductance element has a higher thermal conductivity than the airfoil wall, facilitating heat conduction from the sides into the rib to maintain it at a relatively higher temperature and reduce thermal gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CMC materials are used in airfoils to achieve high temperature resistance, then temperature resistance is improved, but thermal conductivity is reduced leading to thermal gradients and thermally induced stresses
Solution Approach 1:
The patent applies composite materials by combining CMC skins with a metallic core assembly. The CMC outer shell provides high-temperature resistance while the metallic core provides high thermal conductivity. This composite structure resolves the contradiction by allowing the CMC to face the hot gas path (improving temperature resistance) while the metallic core conducts heat away (reducing thermal gradients).
Solution Approach 2:
The patent applies local quality by using different materials in different regions of the airfoil. The CMC material is used where high temperature resistance is needed (outer shell facing the hot gas), while metallic material is used where high thermal conductivity is needed (internal core and ribs). This spatial differentiation of material properties resolves the contradiction between temperature resistance and thermal conductivity.
2Temperature
If traditional cooling methods are applied to CMC airfoils, then temperature reduction is achieved, but thermal gradients and stresses are exacerbated
Solution Approach 1:
The patent introduces a metallic core assembly as an intermediary between the hot CMC outer shell and the cooling system. This metallic core acts as a heat transfer mediator that conducts heat away from critical areas (ribs and transitions) without creating severe thermal gradients in the CMC material itself, thus reducing thermally induced stresses while still achieving temperature reduction.
3Strength
If ribs are added to CMC airfoils for structural support, then mechanical strength is improved, but thermal conductivity is reduced leading to distress from thermally induced stresses
Solution Approach 1:
The patent uses composite materials in the rib structure by incorporating metallic material into the rib assembly. The metallic core assembly includes ribs that provide both structural support and high thermal conductivity. This allows the ribs to maintain mechanical strength while simultaneously conducting heat away from themselves, preventing thermal distress.
4Temperature
If CMC materials are used throughout the airfoil, then high temperature resistance is achieved, but manufacturing complexity increases due to joining requirements
Solution Approach 1:
The patent applies segmentation by dividing the airfoil into distinct modules: CMC outer shell segments and metallic core assembly segments. These segments can be manufactured separately using optimized processes for each material system, then joined together. This modular segmentation reduces overall manufacturing complexity compared to creating a monolithic CMC 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
This design helps in reducing thermal gradients and stresses in the rib, enhancing durability by maintaining the rib at a higher temperature, thus improving the structural integrity and performance of CMC airfoils under high-temperature conditions.
Implementation Method 1
The rib has a thermal conductance element 76 that is configured to conduct heat away from the sides 64c/64d and into the rib 72 to maintain the rib at a relatively higher temperature
Data Source
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AI summary
An airfoil (60) includes an airfoil section (62) that has a ceramic airfoil wall (64) that defines a suction side (64d) and a pressure side (64c). There is an interior cavity (70) in the airfoil section (62). A rib (72) spans across the interior cavity (70) and connects the suction side (64d) and the pressure side (64c). The rib (72) has a thermal conductance element (76) that is configured to conduct heat away from the suction side (64d) and the pressure side (64c).