Variable Volume Turbine Case Clearance Control
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Solution Overview
Problem
Gas turbine engines face challenges in maintaining a consistent radial tip clearance due to thermal expansion and contraction, which affects engine performance across varying operational conditions.
Innovation Solution
An active clearance control system using a radially adjustable Blade Outer Air Seal (BOAS) system with an accumulator system that includes a pneumatic cylinder and a movable piston to maintain a constant volume between air seal segments and the engine case structure, allowing for passive operation and controlled movement to adjust tip clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If hydraulic cylinders and pistons are used for active tip clearance control, then radial tip clearance can be adjusted, but the device complexity and size increase
Solution Approach 1:
The patent extracts the active clearance control function from complex hydraulic positioning mechanisms and implements it through a simplified thermal control system using heated air or gas flow. The thermal expansion of the shroud assembly is controlled by directing hot gas from the turbine to specific regions, eliminating the need for hydraulic cylinders and pistons while maintaining radial tip clearance adjustment capability
Solution Approach 2:
The patent replaces the mechanical hydraulic positioning system with a thermal field-based control system. Instead of using mechanical force from hydraulic actuators to adjust blade tip clearance, the system uses thermal expansion and contraction of the shroud assembly controlled by heated gas flow, substituting a mechanical system with a thermal field system
2Reliability
If radial tip clearance is designed for high power operations, then blade tips do not rub against air seal, but clearance increases when engine power is reduced
Solution Approach 1:
The patent implements a dynamic clearance control system where the shroud assembly's thermal state is continuously adjusted based on engine operating conditions. By controlling the flow of heated gas to specific regions of the shroud, the system dynamically adjusts thermal expansion to maintain optimal radial tip clearance across varying power levels, transitioning from a static design to a dynamic control system
Solution Approach 2:
The patent changes the thermal parameters of the shroud assembly by controlling the temperature and flow of heated gas applied to different regions. By varying these thermal parameters in response to engine power changes, the system maintains consistent radial tip clearance despite changes in engine operating conditions, preventing both blade rub and excessive clearance
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 system effectively maintains a consistent radial tip clearance, reducing the need for larger actuators and improving engine performance by accommodating thermal changes and operational variations.
Implementation Method 1
the thermal environment in the engine varies and may cause thermal expansion and contraction such that the radial tip clearance varies
Implementation Method 2
an active clearance control system using a radially adjustable Blade Outer Air Seal (BOAS) system with an accumulator system that includes a pneumatic cylinder and a movable piston
Data Source
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AI summary
An active clearance control system of a gas turbine engine includes a radially adjustable blade outer air seal system movable between a radially contracted Blade Outer Air Seal (BOAS) position that defines a first air volume and a radially expanded Blade Outer Air Seal (BOAS) position that defines a second air volume, the second air volume different than the first air volume. An accumulator system accommodate a difference in air volume between the first air volume and the second air volume.