Leaf Seal Axial Clearance Leakage Control
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Solution Overview
Problem
Conventional leaf seals in gas turbine engines face a design conflict between minimizing leakage and controlling blow up and blow down performance, due to manufacturing tolerances affecting the ratio of coverplate to leaf pack distances, leading to poor leakage performance or blow control.
Innovation Solution
A leaf seal design with a controlled axial clearance as the dominant flow restriction, allowing for increased distances between coverplates and adjacent packs, and optional features such as varying leaf pack geometries and spacer elements to obscure interleaf gaps, ensuring the axial clearance dictates leakage flow without compromising leakage performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If coverplate to leaf pack distances are minimized to reduce leakage, then leakage performance improves, but blow up and blow down control deteriorates due to manufacturing tolerances affecting the distance ratio
Solution Approach 1:
The invention introduces a second axial dimension by stacking leaf packs in multiple axial layers. Instead of relying solely on coverplate distances in one dimension, the seal performance is controlled through the axial arrangement of multiple leaf pack layers, each contributing to the overall sealing effect and allowing independent optimization of leakage and blow control characteristics.
Solution Approach 2:
Different axial layers of leaf packs can have different interleaf gap configurations, leaf orientations, and stacking patterns. This allows local optimization where certain layers are designed for superior leakage prevention while other layers are optimized for blow up and blow down control, with each layer having tailored properties to its specific functional requirement.
2Reliability
If coverplate to leaf pack distances are increased to improve blow up and blow down control, then blow control improves, but leakage performance deteriorates
Solution Approach 1:
The seal is divided into multiple discrete axial layers of leaf packs, with each layer segmented to have specific interleaf gap patterns. This segmentation allows the total sealing function to be distributed across layers, where each layer contributes partially to both leakage prevention and blow control, eliminating the need to compromise either function by adjusting single-distance parameters.
Solution Approach 2:
The invention creates a composite sealing structure by stacking multiple leaf pack layers with different configurations. Each layer acts as a component material with specific properties, and the combination of layers produces a composite seal that achieves both low leakage and good blow control simultaneously, similar to how composite materials combine different material properties.
3Reliability
If manufacturing tolerances are tight to control distance ratios, then blow up and blow down control improves, but manufacturing complexity and cost increase
Solution Approach 1:
The leaf packs are designed with self-aligning features and tolerance-compensating geometries that allow the assembly to automatically adjust during installation. The stacking arrangement and interleaf gap configurations are designed to be inherently robust to manufacturing variations, reducing the need for tight tolerance control while maintaining reliable blow up and blow down performance.
Solution Approach 2:
The invention changes the critical parameters from precise distance ratios to more tolerant geometric relationships. By using axial stacking with controlled interleaf gaps and leaf orientations, the system becomes less sensitive to absolute distance measurements and more dependent on relative positioning, which can be controlled with standard manufacturing tolerances.
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 enhances blow up and blow down control while maintaining low leakage, reducing sensitivity to manufacturing tolerances and potentially eliminating the need for coverplates, thereby improving overall seal performance.
Implementation Method 1
the controlled axial clearance is the dominant flow restriction in the seal determining the amount of leakage flow through the seal
Implementation Method 2
The leaves 32, and in particular the leaf edges 36 of the leaves 32 act against the surface 37 in order to create a seal across the assembly 31
Data Source
AI summary
A leaf seal has a pair of annular packs of stacked leaves. Each pack is mountable to one of the components with its leaves extending towards the other component such that the leaf edges of at least one of the packs are presented for wiping contact with the other component. The packs are axially spaced from each other by a controlled axial clearance. Within each pack the leaves are stacked face-to-face such that neighboring leaves are separated from each other by interleaf gaps which allow an axial leakage flow through the seal. Further, within each pack the packs are positioned such that, when viewed in the axial direction, the leaves of each pack of the pair substantially obscure the interleaf gaps of the other pack of the pair. The controlled axial clearance is the dominant flow restriction in the seal determining the amount of leakage flow through the seal.