CMC Turbine Ring Assembly Thermal Expansion Clearance
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Solution Overview
Problem
Turbine ring assemblies in gas turbine engines face issues with differential expansion between ceramic matrix composite (CMC) ring sectors and metal ring support structures, leading to mechanical stress and potential damage from high temperatures, as CMC materials expand less than metal and are weakened by thermal stresses.
Innovation Solution
A turbine ring assembly design featuring CMC ring sectors with π-shaped sections and radially extending tabs that fit over metal ring support structure tabs, with pegs providing initial clearance to compensate for differential expansion, and oblong holes for additional expansion compensation, ensuring effective sealing and stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CMC ring sectors are held without radial clearance by the metal ring support structure, then the ring sectors are securely mounted, but the CMC ring sectors are weakened by mechanical stresses from differential expansion at high temperatures
Solution Approach 1:
The invention introduces radial clearance between the CMC ring sector tabs and metal support structure tabs to accommodate differential thermal expansion. The clearance allows the metal structure to expand into the clearance space at high temperatures without imposing excessive compressive stress on the CMC sectors, thereby maintaining their strength while ensuring secure mounting at operating conditions.
2Strength
If the metal ring support structure is placed close to the hot gas flow passage, then structural support is provided, but the metal structure is damaged by high temperature
Solution Approach 1:
The CMC ring sectors act as a thermal barrier intermediary between the hot gas flow passage and the metal ring support structure. By positioning the CMC sectors radially outward from the metal structure and allowing them to contact the hot gas environment, the design protects the metal support structure from direct thermal exposure while maintaining structural support functionality.
3Temperature
If CMC ring sectors are used to replace metal, then weight is reduced and high temperature properties are improved, but the CMC material can only accept very low levels of stress
Solution Approach 1:
The radial clearance design accommodates the lower thermal expansion coefficient of CMC compared to metal by allowing the metal support structure to expand into the clearance space without generating excessive stress on the brittle CMC sectors. This enables the use of CMC's superior high-temperature properties while protecting its low stress-tolerance characteristic.
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 mitigates thermal stress on CMC ring sectors, provides a thermal barrier to protect the metal support structure from hot gases, reduces cooling needs, and lowers fuel consumption by maintaining structural integrity and sealing efficiency.
Implementation Method 1
CMC ring sectors can accept only very low levels of stress, they have high stiffness, and they expand much less than the metal ring support structure. Consequently, since according to the above-mentioned document the ring sectors are held without radial clearance, if ever they are subjected to very high temperatures they are weakened as a result of the mechanical stresses imposed by the differential expansion relative to the ring support structure.
Implementation Method 2
the ring support structure is made of metal and is close to the flow passage for hot gas so that it is subjected to a considerable temperature rise. The metal structures are thus in a danger of being damaged by the high temperature of the gas in the passage.
Data Source
AI summary
A turbine ring assembly includes ring sectors made as a single piece of ceramic matrix composite material and being for mounting on a metal ring support structure, the ring support structure having two tabs extending radially towards a gas flow passage, each ring sector having a first portion forming an annular base with a radially inside face defining the inside face of the turbine ring and an outside face from which there extend two tab-forming portions, the ring sectors having a section that is substantially π shaped. The tabs of each ring sector fit axially over the tabs of the ring support structure with contact between the tabs of the ring support structure and the tabs of each ring sector when cold. The tabs of each ring sector are held to the ring support structure by pegs passing through holes formed in the tabs of each ring sector.