CMC Turbine Nozzle Stage Compression Mounting
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Solution Overview
Problem
Ceramic matrix composite (CMC) materials used in turbine nozzle stages are sensitive to mechanical stresses and thermal expansion differences with metal environments, making integration and sealing challenging, especially in high-pressure turbine engines where thermal and aerodynamic forces are high.
Innovation Solution
A turbine engine design featuring a CMC nozzle stage clamped between a casing and a metal ring with an enlarged outer diameter, which compresses the nozzle stage, utilizing a metal ring with a smaller inside diameter to enhance sealing and reduce leakage risks, and incorporating features like crenellated annular ribs and gaskets for improved axial and rotational stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CMC material is used for turbine nozzle stage, then temperature tolerance is improved, but mechanical stress sensitivity worsens
Solution Approach 1:
The patent changes the stress state parameter from tension to compression by using a metal ring that applies compressive force to the CMC nozzle stage. This resolves the contradiction because CMC materials have superior compressive strength compared to their tensile strength, allowing them to withstand mechanical stresses better when operated in compression rather than tension.
2Temperature
If CMC nozzle stage is integrated in metal environment, then temperature resistance is improved, but thermal expansion compatibility worsens
Solution Approach 1:
The patent explicitly addresses thermal expansion compatibility by designing the metal ring with a larger thermal expansion coefficient than the CMC nozzle stage. The metal ring is made of superalloy or titanium alloy while the nozzle stage is made of CMC material. This differential expansion is managed through the interference fit design where the metal ring is heated for assembly and then contracts upon cooling, creating a compressive pre-stress that accommodates thermal expansion differences during operation.
3Reliability
If metal ring with enlarged outer diameter is used, then sealing is improved, but device complexity worsens
Solution Approach 1:
The patent applies local quality by concentrating the sealing function in a specific local area - the interference fit interface between the metal ring and the nozzle stage. The metal ring's enlarged outer diameter creates a localized interference fit zone that provides sealing without requiring complex sealing mechanisms throughout the entire assembly. This localized approach improves sealing while minimizing overall device complexity.
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 design simplifies mounting, enhances the structural rigidity and sealing of the CMC nozzle stage, reduces the risk of leaks, and optimizes the use of CMC properties by operating in compression, while minimizing the number of parts and contacts, thus improving the overall performance and reliability of the turbine engine.
Implementation Method 1
the metal ring is cooled in order to reduce its diameter prior to being inserted and put into position inside the annulus formed by the annular sectors of the nozzle stage. Once in alignment with the plane in which the nozzle stage extends, the metal ring is returned to ambient temperature so as to recover its original diameter and exert a radial force
Implementation Method 2
the majority of the CMC nozzle work in compression
Data Source
AI summary
A turbine engine turbine including a nozzle stage made of ceramic matrix composite material and including a plurality of annular sectors forming an annulus presenting an inner shroud and an outer shroud, each sector having an inner platform forming a portion of the inner shroud, an outer platform forming a portion of the outer shroud, and at least one airfoil extending between the outer and inner platforms and secured thereto. A metal ring includes at least one annular sector, and presents an outer surface in contact with the surface of the inner shroud opposite from the surface from which the airfoils extend, the metal ring presenting an outside diameter at its outer surface that is greater than the diameter of the inner shroud such that the nozzle stage is held in compression between a casing and the metal ring.