Turbine Combustor Liner Mounting Assembly for CMC Thermal Stress
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Solution Overview
Problem
The mechanical properties of ceramic matrix composite (CMC) materials used in gas turbine engines, such as differing coefficients of thermal expansion, pose challenges in attaching the outer and inner liners to their respective metallic domes, leading to premature wear and excessive stress.
Innovation Solution
A mounting assembly featuring a pin, bushing, and metal grommet is used to attach the forward end of the liners to the annular domes, with the grommet having an inner and outer collar to protect the liners and accommodate thermal expansion, reducing wear and stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional metal attachment mechanisms are used to attach CMC liners to metallic domes, then the attachment provides structural support, but the differing coefficients of thermal expansion cause premature wear and excessive stress on the components
Solution Approach 1:
A metallic grommet with inner and outer collars is introduced as an intermediary component between the CMC liner and the metallic dome. The grommet accommodates differential thermal expansion by allowing relative movement while distributing stresses, preventing direct contact and wear between the liner and dome attachment mechanisms. This mediator resolves the contradiction by enabling reliable attachment while extending component lifespan through stress distribution and wear prevention.
Solution Approach 2:
The attachment system is designed to change its mechanical parameters dynamically in response to thermal conditions. The grommet allows for variable clearance and movement characteristics that adapt to thermal expansion differences between CMC and metal components. By changing the effective stiffness and clearance parameters based on temperature, the system maintains reliable attachment while preventing excessive stress accumulation that would reduce component lifespan.
2Strength
If rigid attachment mechanisms are used to secure the liner to the dome, then strong structural support is provided, but the mechanism cannot accommodate thermal expansion differences, leading to premature wear
Solution Approach 1:
The attachment mechanism transitions from a static rigid connection to a dynamic system that accommodates thermal movement. The grommet enables controlled relative movement between the liner and dome while maintaining attachment strength. This dynamic capability allows the system to absorb thermal expansion differences without compromising attachment strength or durability, resolving the contradiction between strong support and wear prevention.
Solution Approach 2:
The metallic grommet serves as a compliant intermediary that maintains strong attachment while accommodating thermal movement. It provides a flexible connection point that preserves structural strength through its collar design while allowing the necessary relative movement to prevent wear, thus maintaining both attachment strength and reliability under thermal cycling conditions.
3Device complexity
If the liner is directly attached to the dome without protective elements, then the attachment mechanism is simple, but the liner experiences premature wear and stress from relative movement
Solution Approach 1:
A metallic grommet with inner and outer collars is introduced as a protective intermediary between the liner and the attachment mechanism. This relatively simple component prevents direct wear between the liner and dome by providing a protective interface that accommodates relative movement. The grommet extends liner lifespan while adding minimal complexity to the attachment system, resolving the contradiction between simplicity and durability.
Solution Approach 2:
The grommet provides beforehand cushioning by pre-positioning protective collars that cushion the liner against wear before relative movement occurs. The inner collar protects the liner's outer surface, while the outer collar protects the dome's inner surface, preventing premature wear through advance protection that minimizes liner lifespan reduction without significantly increasing attachment 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 solution effectively reduces wear and stress on the components by allowing for relative movement and thermal expansion, ensuring reliable attachment and prolonged component lifespan.
Implementation Method 1
CMC materials have different coefficients of thermal expansion than the traditional metal materials. Such differing mechanical properties can make it difficult to attach the outer liner to an outer metallic dome and the inner liner to an inner metallic dome.
Data Source
AI summary
A combustor assembly for a gas turbine engine is provided. The combustor assembly generally includes an annular dome and a liner. The liner at least partially defines a combustion chamber and includes the forward end received within a slot defined by the annular dome. A mounting assembly attaches the forward end of the liner to the annular dome. The mounting assembly includes a pin extending through the slot and the forward end of the annular dome. The mounting assembly also includes a grommet positioned in an opening in the forward end of the liner. The grommet is also positioned around the pin to protect the liner during operation of the gas turbine engine.