Offset Seal Assembly for Gas Turbine Casing Deflection
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Solution Overview
Problem
Conventional gas turbine engines face challenges in managing roll torque wind-up due to increased aerodynamic loading and torque in geared turbofan configurations, leading to excessive angular displacement of the nacelle, which requires additional structural mass to resist torque wind-up and maintain a seal at the pylon-nacelle interface.
Innovation Solution
A seal assembly with a static support structure and a casing structure that includes a first and second seal portion, offset from their equilibrium position when the engine is at rest, to accommodate mechanical and thermal deflections, ensuring a consistent seal interface during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the span of outlet guide vanes is increased to accommodate higher bypass ratio and aerodynamic loading, then the distance between core casing and nacelle is increased, but the roll torque wind-up increases causing excessive angular displacement of the nacelle
Solution Approach 1:
The seal assembly is pre-positioned with an offset from the equilibrium position in the at-rest state. This preliminary positioning anticipates the direction of casing deflection during operation, allowing the seal portions to be pre-compressed or pre-tensioned to counteract the expected roll torque wind-up and maintain sealing effectiveness throughout the operational deflection range
2Stability of the object's composition
If additional mass is added to strengthen the outlet guide vanes to resist torque wind-up, then the angular displacement of the nacelle is reduced, but the engine weight increases
Solution Approach 1:
The seal assembly utilizes differential compression of its seal portions to adapt to operational conditions. By having the first and second seal portions compressed by different amounts during operation, the system can accommodate the expected angular displacement without requiring additional structural mass, effectively changing the mechanical parameters of the seal to match the operational deflection range
3Stability of the object's composition
If the gap at the pylon or nacelle interface is increased to accommodate larger angular displacement, then the seal effectiveness is reduced, but the aerodynamic leakage increases
Solution Approach 1:
The seal assembly is pre-positioned with an offset from the equilibrium position in the at-rest state. This preliminary positioning anticipates the direction of casing deflection during operation, allowing the seal portions to be pre-compressed or pre-tensioned to counteract the expected roll torque wind-up and maintain sealing effectiveness throughout the operational deflection range
Solution Approach 2:
The seal assembly utilizes differential compression of its seal portions to adapt to operational conditions. By having the first and second seal portions compressed by different amounts during operation, the system can accommodate the expected angular displacement without requiring additional structural mass, effectively changing the mechanical parameters of the seal to match the operational deflection range
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 seal assembly effectively reduces the need for additional structural stiffness, allowing for a more tolerant seal interface to mechanical and thermal deflections, thereby reducing engine weight and improving fuel efficiency by minimizing aerodynamic steps and leakage.
Implementation Method 1
a seal at an interface between the static support structure and the casing structure, and comprising a first seal portion and a second seal portion spaced from one another in the first direction, wherein the first seal portion is provided against a first surface of the casing structure and the second seal portion is provided against a second surface of the casing structure opposing the first surface
Data Source
AI summary
A seal assembly for a gas turbine engine having a rotor arranged to rotate about an axis in use. The seal assembly has a static support structure for the gas turbine engine and a casing structure of the engine. Rotation of the engine rotor causes a deflection of the casing structure relative to the static support structure in a first direction. A seal is provided at an interface between the static support structure and the casing structure, and comprising a first seal portion and a second seal portion spaced from one another in the first direction. The first seal portion is provided against a first surface of the casing structure and the second seal portion is provided against a second surface of the casing structure opposing the first surface. In an at-rest state in which the engine is not operational, the first and second surfaces are offset from an equilibrium position with respect to the static support structure such that there is a difference in compression of the first seal portion and the second seal portion between the static support structure and the casing structure. The offset is in a direction opposite to the first direction.