Shape Memory Alloy Brush Seal for Passive Clearance Control
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Solution Overview
Problem
In high-pressure differential applications, typical brush seals in gas turbine engines experience increased bristle wear due to bristle blow-down, which affects seal performance and longevity.
Innovation Solution
A brush seal design featuring bristles made from shape memory alloys that curl away from the backing plate and towards the retention structure as temperature increases, providing passive clearance control and reducing wear by deforming from a martensite to austenite phase, thus minimizing contact with the radial surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If typical brush seals are used in high pressure differential applications, then sealing function is provided, but bristle wear increases due to bristle blow-down
Solution Approach 1:
The bristle pack is designed to dynamically adjust its configuration in response to temperature changes. As temperature increases, the bristle pack transitions from a straight configuration to a curved configuration, automatically adapting to thermal expansion and pressure differential conditions without external control mechanisms.
Solution Approach 2:
The invention utilizes temperature as a controlling parameter to change the physical state and configuration of the bristle pack. The phase transition of the shape memory alloy bristles from martensite to austenite upon heating causes the bristle pack to curve, thereby changing its mechanical properties and contact characteristics with the sealing surface.
2Stress or pressure
If bristle pack is designed to resist high pressure differentials, then sealing effectiveness is improved, but bristle blow-down increases leading to wear
Solution Approach 1:
The bristle pack is pre-configured with curvature that anticipates the direction of blow-down forces. The initial curved shape positions the bristles to better resist the expected pressure differential-induced blow-down, reducing the magnitude of harmful forces acting on the bristles during operation.
Solution Approach 2:
The bristle pack dynamically changes its configuration in response to temperature-induced thermal expansion. As the engine operates and temperature rises, the bristle pack curves further, automatically adjusting its geometry to maintain optimal contact and reduce blow-down effects under varying pressure conditions.
3Duration of action of moving object
If shape memory alloy bristles are used to provide passive clearance control, then bristle wear is reduced, but device complexity increases
Solution Approach 1:
The shape memory alloy bristles possess self-service capabilities by automatically changing their configuration in response to temperature changes. The material's inherent phase transition properties enable the bristle pack to self-adjust its curvature and contact characteristics without requiring external actuators, control systems, or additional mechanical components.
Solution Approach 2:
The invention exploits the phase transition characteristics of shape memory alloys. When heated, the bristles undergo a martensite-to-austenite phase transition, which causes them to curve and change their mechanical behavior. This phase transition mechanism provides the passive clearance control function inherently, without adding structural complexity.
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 solution effectively reduces bristle wear and enhances seal performance by allowing the bristles to curl away from the sealing surface, counteracting the downward force from pressure differentials and maintaining effective sealing during operation.
Implementation Method 1
the bristle pack comprises shape memory alloys and is configured to have a passive clearance control. For example, as the first bristle pack increases in temperature, each bristle in the first bristle pack may go through a phase transformation from martensite to austenite whereby they plastically deform into a parent shape
Implementation Method 2
as the first bristle pack increases in temperature, each bristle in the first bristle pack may go through a phase transformation from martensite to austenite
Implementation Method 3
each bristle in the first bristle pack may go through a phase transformation from martensite to austenite whereby they plastically deform into a parent shape
Data Source
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AI summary
A brush seal (350) may comprise a bristle pack (356) including at least one bristle (571) made of a shape memory alloy. The bristle may be used in a sealing system. The brush seal may be disposed in a seal cavity (340). The brush seal may further comprise backing plate (352) and a retention structure (354) coupled to the bristle pack. The brush seal may be configured for passive clearance control during operation of a gas-turbine engine (120).