Stand-off Device for Double-Skin Combustor Liner Thermal Expansion
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Solution Overview
Problem
In gas turbine engines, maintaining the air gap between ceramic matrix composite (CMC) and metallic combustor liners with different coefficients of thermal expansion is challenging, requiring effective spacing mechanisms to accommodate thermal expansion while ensuring durability and cooling efficiency.
Innovation Solution
The use of stand-off devices with a body having a first and second end, where the second end is retained in the outer combustor skin and the first end abuts the inner combustor skin, maintaining a spacing gap and allowing for thermal expansion, with optional coatings for reduced friction and biasing assemblies for additional support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the air gap between metallic outer shell and CMC combustor ring is maintained to accommodate different coefficients of thermal expansion, then thermal expansion compatibility is improved, but device complexity increases due to the need for stand-off devices
Solution Approach 1:
A stand-off device with a body and protrusion acts as an intermediary element between the metallic outer shell and CMC combustor ring. The protrusion engages with the CMC ring while the body is retained by the outer shell, mediating the thermal expansion differences between the two materials and maintaining the required air gap without direct contact
Solution Approach 2:
The stand-off device is segmented into distinct functional parts: a body portion retained by the outer shell and a protrusion portion engaging with the CMC ring. This segmentation allows each part to be optimized for its specific function while collectively solving the thermal expansion compatibility issue
2Manufacturing precision
If stand-off devices are used to maintain spacing between combustor skins, then spacing maintenance is improved, but frictional wear increases at the contact interface
Solution Approach 1:
A coating layer is applied to the surface of the stand-off device that contacts the CMC combustor ring. This coating layer reduces frictional wear at the contact interface while maintaining the precise spacing function, protecting the stand-off device from harmful frictional effects
Solution Approach 2:
The surface properties of the stand-off device are modified through coating application, changing the friction parameter at the contact interface. This reduces the coefficient of friction and wear while maintaining the mechanical spacing function
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 effectively maintains the necessary spacing between CMC and metallic combustor skins, accommodating thermal expansion and enhancing durability and cooling efficiency, while preventing frictional wear and ensuring effective sealing and cooling performance.
Implementation Method 1
the second end of the body retained in an opening in the outer combustor skin
Implementation Method 2
the air gap between the metallic outer shell and the annular CMC combustor ring or the CMC combustor panels must be maintained, in spite of the different coefficients of thermal expansion involved
Data Source
AI summary
A combustor for a gas turbine engine comprises a combustor chamber defined at least partially by an outer combustor skin and an inner combustor skin. A plurality of stand-off devices have a body including a first end and a second end, the second end of the body retained in an opening in the outer combustor skin, the first end spaced apart from the second end and abutting the inner combustor skin to space the inner combustor skin apart from the outer combustor skin.