Overhanging Seal Assembly for Gas Turbine CMC Leakage
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Solution Overview
Problem
In gas turbines, the thermal expansion mismatch between ceramic matrix composite (CMC) components and traditional high-temperature nickel alloy seals leads to seal shifting and potential crushing, resulting in leakage issues that affect performance and efficiency.
Innovation Solution
An overhanging seal assembly is designed, comprising an intersegment seal and two overhanging positioner shim seals with extended portions, which are positioned to constrain the vertical seal segments and prevent shifting, addressing the thermal expansion mismatch and enhancing sealing at corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional high-temperature nickel alloy seals are used with CMC components, then sealing function is provided, but thermal expansion mismatch causes seal shifting and crushing
Solution Approach 1:
The seal assembly is divided into multiple segments: vertical seal segments for primary sealing, horizontal seal segments for corner sealing, and overhanging positioner shim seals for positional constraint. This segmentation allows each component to perform its specific function while accommodating thermal expansion differences between CMC and nickel alloy materials.
Solution Approach 2:
The overhanging positioner shim seals act as intermediary elements between the vertical seal segments and the seal slot walls. These positioners prevent direct contact and friction between the expanding vertical seals and the CMC shroud, mediating the thermal expansion mismatch and preventing seal shifting and crushing.
2Adaptability or versatility
If seal length is reduced to account for CTE mismatch, then thermal expansion compatibility improves, but seal flexibility and sealing capability deteriorate
Solution Approach 1:
The seal design transitions from traditional single-plane seals to a three-dimensional overhanging configuration. The overhanging positioner shim seals extend beyond the primary seal plane, creating additional dimensional space for positional constraint without interfering with the primary sealing function. This dimensional addition allows shorter seals to maintain both thermal compatibility and sealing effectiveness.
Solution Approach 2:
The overhanging positioner shim seals provide dynamic positional constraint that adapts to thermal expansion. As the nickel alloy seals expand with temperature, the positioners maintain contact and guide the expansion movement, preventing unwanted shifting while allowing the seals to maintain their sealing function throughout the thermal cycle.
3Reliability
If multiple separate seal components are used, then sealing coverage is improved, but assembly complexity increases
Solution Approach 1:
Multiple sealing functions are merged into a single integrated overhanging seal assembly. The vertical seal segments, horizontal seal segments, and overhanging positioner shim seals are assembled together as one unit that installs into the seal slot as a complete system. This merging maintains comprehensive sealing coverage while simplifying the installation process compared to installing multiple separate seal components independently.
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 overhanging seal assembly effectively minimizes leakage between CMC turbomachinery components, maintains seal positioning, and accommodates thermal expansion, ensuring robust and flexible sealing while reducing part count and assembly complexity.
Implementation Method 1
the thermal expansion mismatch between ceramic matrix composite (CMC) components and traditional high-temperature nickel alloy seals leads to seal shifting and potential crushing
Implementation Method 2
The extended portions of the overhanging seal segments are disposed in the seal slot on an interior side of the seal slot and adjacent one of the plurality of horizontal seal segments so as to provide position constrainment of the two vertical seal segments
Data Source
AI summary
Various embodiments include gas turbine seals and methods of forming such seals for advanced gas path (AGP) heat transfer designed gas turbine engines. In some cases, a turbine includes: a first arcuate component adjacent to a second arcuate component, each arcuate component formed of a ceramic matrix composite and including a seal slot located in an end face, each seal slot having a plurality of axial surfaces and radially facing surfaces extending from opposite ends of the axial surfaces and an overhanging seal assembly disposed in the seal slot. The overhanging seal assembly including an intersegment seal including a plurality of seal segments defining two vertical seal segments and a plurality of horizontal seal segments and a first overhanging positioner shim seal and a second overhanging positioner shim seal, each including an extended portion. The overhanging seal assembly disposed in the seal slot so as to provide position constrainment of the two vertical seal segments.