Split CMC Turbine Ring Assembly Thermal Expansion Management
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Solution Overview
Problem
The assembly of turbine rings in gas turbines using thermostructural composite materials (CMC) faces challenges in minimizing gas leaks and accommodating differential expansion between CMC and metal components, requiring complex designs and significant cooling airflow.
Innovation Solution
A simplified assembly using a one-piece split CMC ring with a wedge-shaped piece and an annular metal structure, where the CMC ring is prestressed and mounted with elastic return elements to maintain contact and minimize leaks, along with a metal ring encircling the CMC ring to manage thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a CMC ring is used to reduce cooling requirements and improve efficiency, then cooling airflow is reduced, but differential expansion between CMC and metal components causes complex assembly design requirements
Solution Approach 1:
The CMC ring is divided into multiple sectors that can be assembled separately around the turbine wheel, allowing each sector to be independently managed for thermal expansion while maintaining the overall ring structure. This segmentation simplifies the assembly process compared to a fully complex differential expansion design.
Solution Approach 2:
Metal support structures serve as intermediary elements between the CMC ring sectors, providing a transition zone that accommodates differential thermal expansion. These supports act as mediators that absorb expansion differences without requiring complex direct coupling designs between CMC components.
2Temperature
If CMC ring sectors are mounted in a metal support to accommodate differential expansion, then thermal expansion is managed, but gas leaks between adjacent sectors increase
Solution Approach 1:
Flexible sealing elements or thin film seals are introduced between adjacent CMC ring sectors and between the ring and metal support. These flexible sealing layers accommodate thermal expansion movements while maintaining gas tightness, preventing leaks without restricting thermal management.
Solution Approach 2:
The sealing interface design incorporates parameter changes in the form of compliant sealing materials that change their physical properties (such as elasticity or hardness) with temperature, allowing them to maintain effective sealing across the thermal expansion range while preventing gas leaks.
3Device complexity
If a one-piece CMC ring is used to simplify assembly structure, then assembly complexity is reduced, but maintaining contact under differential expansion becomes challenging
Solution Approach 1:
The connection between the CMC ring and metal support incorporates dynamic elements that allow for movement and adjustment during thermal expansion. This dynamic design maintains reliable contact between components throughout the expansion cycle without requiring complex static restraint structures.
Solution Approach 2:
The design explicitly incorporates thermal expansion compensation mechanisms, such as expansion joints or compliant mounting structures, that allow the CMC ring to expand and contract while maintaining reliable contact with the metal support. This approach simplifies the overall assembly by working with rather than against thermal expansion.
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 solution reduces the complexity of assembly, minimizes gas leaks, and decreases cooling requirements by using a self-healing CMC material with an environmental barrier coating, enhancing the structural integrity and efficiency of the turbine ring.
Implementation Method 1
the CMC ring being mounted with prestress in the metal structure
Implementation Method 2
when the slot opens under the effect of a differential expansion between the annular metal structure and the CMC ring
Implementation Method 3
at least one element exerting an elastic return force on the wedge-shaped part to keep the latter in contact with the ends of the ring
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A turbine ring assembly for a gas turbine comprises a split ring (10) in a single piece of composite ceramic matrix material (CMC), a wedge-shaped part (20) made of CMC with the sides in contact with the ends of the ring, at both sides of the split, for closing the ring, and an annular metallic support structure (40) encircling the CMC ring and in contact with the latter over the greater part of the contour thereof, the CMC ring being fitted with preconstraint in the metallic structure, at least one element (26) exerting an elastic recoil force on the wedge-shaped part in order to keep the latter in contact with the ends of the CMC ring when the split opens under the effect of a differential dilation between the annular metallic structure and the CMC ring, and at least one element for locking for the CMC in rotation around its axis.