Outer Air Seal Assembly With Movable Segments for Blade Tip Clearance
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Solution Overview
Problem
Existing outer air seal (OAS) assemblies in gas turbine engines for aircraft propulsion systems face challenges in efficiently managing blade tip clearance and sealing, particularly due to variations in radial positions of rotor blades caused by thermal and centrifugal expansion, leading to inefficiencies and potential contact issues.
Innovation Solution
The design incorporates a plurality of OAS segments with radially moveable seal bodies and a compliant air seal that biases the segments towards an inboard position, forming a shiplap joint and abradable seals to manage blade tip clearance, minimizing leakage and preventing excessive contact, while accommodating thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed OAS assembly is used, then the structure is simple, but it cannot accommodate thermal expansion and centrifugal growth of rotor blades, leading to excessive blade tip clearance and air flow leakage
Solution Approach 1:
The OAS assembly employs radially moveable segments instead of a fixed structure. Each segment can independently move radially to maintain optimal blade tip clearance as the rotor blades expand thermally and centrifugally during operation, transforming the static seal into a dynamic adaptive system.
Solution Approach 2:
The OAS assembly is divided into multiple radially moveable segments rather than a single fixed component. This segmentation allows each segment to independently adjust its radial position to accommodate varying blade tip clearances caused by thermal and centrifugal effects, improving overall clearance control reliability.
2Loss of energy
If the OAS segments are positioned outboard to reduce blade tip clearance, then leakage is reduced, but the risk of excessive contact between rotor blades and OAS segments increases
Solution Approach 1:
The radially moveable segments can dynamically adjust their position based on operating conditions. During high-speed operation when centrifugal growth is minimal, segments move outboard to reduce leakage. During thermal expansion phases, segments can move inboard to prevent excessive contact, providing adaptive control of the blade tip clearance.
Solution Approach 2:
The radial position parameter of the OAS segments is made variable rather than fixed. By changing the radial position of segments in response to operating conditions (temperature, speed), the system optimizes the balance between minimizing leakage and preventing excessive contact.
3Adaptability or versatility
If a single piece OAS assembly is used, then manufacturing is simple, but it cannot adapt to varying operating conditions and blade tip clearance requirements
Solution Approach 1:
Dividing the OAS assembly into multiple segments enables adaptability to varying operating conditions, as each segment can independently adjust its radial position. The segments are manufactured separately and then assembled together, which while slightly more complex than a single-piece design, provides the necessary adaptability for different clearance requirements.
Solution Approach 2:
The segmented design allows the OAS assembly to serve multiple functions: sealing at different radial positions, accommodating thermal expansion, compensating for centrifugal growth, and adapting to various operating conditions. Each segment acts as a universal element that can function at different positions along the radial axis.
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 enhances compressor efficiency by reducing air flow leakage and minimizing physical contact between rotor blades and OAS segments, optimizing blade tip clearance control across varying operating conditions.
Implementation Method 1
The air seal is positioned radially between and contacting the case and the seal body. The air seal biases each of the plurality of OAS segments towards the inboard radial position.
Implementation Method 2
each of the plurality of OAS segments may further include an abradable seal disposed at the inner radial face
Data Source
AI summary
A gas turbine engine includes a bladed rotor, a case, and an outer air seal (OAS) assembly. The bladed rotor includes a plurality of rotor blades each extending to a blade tip. The case circumscribes the bladed rotor. The case forms an OAS cavity at the rotor stage. The OAS assembly includes a plurality of OAS segments and an air seal. The plurality of OAS segments are disposed within the OAS cavity. Each of the OAS segments is radially moveable within the OAS cavity between and to an inboard radial position and an outboard radial position. The air seal is positioned radially between and contacting the case and the seal body. The air seal biases each of the plurality of OAS segments towards the inboard radial position.