Double Lap Joint Heat Shield for Gas Turbine Sealing
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Solution Overview
Problem
Gas turbine engine heat shields face challenges in minimizing bleed air leakage through circumferential thermal expansion gaps, leading to vibration and deformation issues that affect sealing efficiency and engine performance.
Innovation Solution
The implementation of a double circumferential lap joint using an outer cover and alignment tab, which forms an interference fit with heat shield segments to create a pinching preload and bridge the thermal expansion gap, thereby reducing bleed air leakage and accommodating axial thermal growth without loose or tight fits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single lap joint cover plate is used to bridge the circumferential thermal expansion gap, then bleed air leakage is minimized, but the cover plate may lift during assembly and deformation occurs yielding the heat shield segments
Solution Approach 1:
The single cover plate is segmented into an outer cover and an alignment tab that function as separate but coordinated components. The outer cover bridges the gap to prevent bleed air leakage, while the alignment tab provides structural support and prevents lifting during assembly. This segmentation allows each component to specialize in one function, resolving the contradiction between sealing effectiveness and assembly reliability.
Solution Approach 2:
The alignment tab is nested within the overall heat shield segment structure, with its leading edge positioned to engage with the adjacent heat shield segment. This nesting arrangement allows the alignment tab to provide internal support without adding external complexity, preventing cover plate lift while maintaining a compact design that doesn't interfere with the outer cover's sealing function.
2Adaptability or versatility
If heat shield retainers provide a relatively loose axial interface to accommodate thermal growth, then thermal expansion is accommodated, but vibration occurs causing wear on adjacent components
Solution Approach 1:
The double lap joint configuration creates a flexible yet stable connection that can accommodate axial thermal growth through controlled movement. The overlapping structure of the outer cover and alignment tab allows for thermal expansion while maintaining continuous contact with adjacent components, preventing the loose interface vibration that would occur with a single loose retainer while still accommodating the necessary thermal growth.
3Object-affected harmful factors
If heat shield retainers provide a relatively tight axial interface to prevent vibration, then wear on components is reduced, but deformation occurs yielding the heat shield segments
Solution Approach 1:
The double lap joint creates a dynamic interface that adapts to thermal conditions. During cold assembly, the alignment tab and outer cover provide a relatively tight fit that prevents vibration and wear. As thermal growth occurs during operation, the structure dynamically adjusts to accommodate expansion without creating deformation forces, maintaining segment integrity while preventing harmful vibrations.
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 seals the circumferential gaps, reduces wear on components, and maintains sealing efficiency by minimizing vibration and deformation, enhancing the overall performance and efficiency of the gas turbine engine.
Implementation Method 1
the outer cover and the alignment tab may form an interference fit with the second heat shield segment
Implementation Method 2
the first heat shield segment, the second heat shield segment and the outer cover may define an interference fit with the flange to generate a pinching preload
Implementation Method 3
A circumferential thermal expansion gap is defined between a first circumferential heat shield segment and a second circumferential heat shield segment
Data Source
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AI summary
A heat shield assembly for a gas turbine engine includes a first heat shield segment defined about an axis and a second heat shield segment defined about the axis. A double circumferential lap joint is defined between the first heat shield segment and the second heat shield segment.