Hydrostatic Seal Aft Tooth Layout for Stable Flow Jets
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Solution Overview
Problem
Hydrostatic seals in gas turbine engines face issues with variability in high-speed jet behavior and undesirable aero-mechanical properties due to pressure variations, leading to reduced performance and potential vibration-induced stress, especially in longer axial lengths.
Innovation Solution
The hydrostatic seal design includes a cluster of teeth with an aft tooth positioned closer to the aft end, axially spaced greater than 50% of the shoe's axial length, which stabilizes flow and improves pressure characteristics by altering the lifting force balance and reducing dynamic unsteadiness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the seal uses tight clearances to improve sealing performance, then leakage is reduced, but the flow under the seal shoe exhibits high-speed jet variability resulting in negative performance
Solution Approach 1:
The seal teeth are divided into multiple clusters (first cluster and second cluster) spaced apart axially. This segmentation allows each cluster to manage specific flow regions, stabilizing the high-speed jet behavior by breaking up continuous flow into controlled segments, thereby maintaining sealing performance while reducing flow variability
Solution Approach 2:
The second cluster of teeth acts as an intermediary element between the first cluster and the downstream flow. It modifies the flow characteristics by creating a controlled pressure distribution that stabilizes the jet behavior, serving as a mediator that improves flow stability without compromising the tight clearance sealing
2Area of stationary object
If the seal axial length is increased to improve sealing coverage, then more area is sealed, but undesirable aero-mechanical properties and vibration-induced stress increase
Solution Approach 1:
The axial length is utilized efficiently by segmenting teeth into multiple clusters separated by spacing. This allows the seal to achieve adequate sealing coverage without requiring excessive axial length, thereby reducing the overall seal size and associated vibration-induced stress while maintaining effective sealing area
Solution Approach 2:
The axial spacing between tooth clusters is optimized to change the pressure distribution and aero-mechanical properties. By carefully selecting the spacing parameter, the seal achieves stable flow characteristics and reduced vibration stress while maintaining adequate sealing coverage
3Manufacturing precision
If pressure differential is developed across the seal to enable tracking, then the seal maintains clearances, but pressure variations downstream cause undesirable aero-mechanical properties
Solution Approach 1:
The second cluster of teeth serves as an intermediary that stabilizes the pressure distribution downstream. It acts as a flow control element that mitigates adverse pressure variations, thereby maintaining aero-mechanical stability while allowing the pressure differential needed for clearance tracking to 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 design enhances sealing performance by improving damping characteristics and stabilizing flow jets, resulting in reduced vibration and extended seal life.
Implementation Method 1
Hydrostatic seals involve motion of a spring-attached shoe whose response is based on aerodynamic forces developed between the seal shoe and a rotor surface during operation
Implementation Method 2
The aft tooth is axially spaced from the cluster of teeth, the axial spacing of the aft tooth from the cluster of teeth being greater than 50% of the axial length of a sealing surface of the shoe
Implementation Method 3
Hydrostatic seals exhibit less leakage compared to traditional knife edge seals while exhibiting a longer life than brush seals
Data Source
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AI summary
A hydrostatic seal (100) configured to be disposed between relatively rotatable components. The seal includes a base (107). The seal further includes a shoe (108) operatively coupled to the base and extending axially from a forward end (122) to an aft end (124). The seal yet further includes a plurality of teeth (118) extending radially from a sealing surface (110) of the shoe, one of the teeth being an aft tooth (118A) located closer to the aft end than to the forward end of the shoe.