Turbine Shroud Ring Retention System for Clearance Control
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Solution Overview
Problem
In gas turbine engines, maintaining optimal clearance between rotating blade tips and static structures is challenging due to thermal excursions and varying growth rates, leading to suboptimal performance and potential contact issues, which affects thermodynamic efficiency and fuel burn.
Innovation Solution
A retention and control system using a non-metallic shroud ring with a metallic support ring, retention spring, and alignment ring to axially locate and concentrically position the shroud ring, minimizing thermal growth and uniformly spreading loads, while maintaining precise alignment and cooling to reduce thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the clearance between blade tips and static structure is reduced to improve performance, then thermodynamic efficiency is improved, but the risk of contact between blade tips and static structure increases
Solution Approach 1:
The shroud ring is designed to be movable in the radial direction rather than fixed, allowing it to dynamically adjust its position to maintain optimal clearance. The control ring mechanism enables the shroud ring to move radially outward in response to centrifugal forces and thermal expansion of the rotor, and radially inward when these forces decrease, thereby maintaining a consistent gap between blade tips and the shroud ring throughout operation.
Solution Approach 2:
The system changes the radial position parameter of the shroud ring dynamically based on operating conditions. By using the control ring mechanism, the radial distance between the shroud ring and rotor center can be adjusted continuously, allowing the clearance to be optimized for different rotational speeds and thermal states, thus preventing blade contact while maximizing efficiency.
2Reliability
If excess clearance is provided to avoid blade contact, then reliability is improved, but thermodynamic efficiency deteriorates
Solution Approach 1:
Rather than using a fixed excess clearance, the shroud ring is made dynamically adjustable through the control ring mechanism. This allows the system to maintain minimal necessary clearance under normal conditions for optimal efficiency, while automatically increasing clearance when centrifugal or thermal expansion forces require it, thus avoiding blade contact only when necessary.
3Strength
If the shroud ring is made of metallic material for strength, then strength is improved, but thermal growth rate increases relative to blade tips
Solution Approach 1:
The system uses a composite construction where the shroud ring is made of non-metallic material (such as ceramic matrix composite) that has low thermal expansion characteristics, while the control ring is made of metallic material providing mechanical strength and controllability. This combination allows the shroud ring to maintain dimensional stability under thermal conditions while the metallic control ring provides the necessary mechanical properties for actuation and structural support.
Solution Approach 2:
The retention system is divided into separate functional components: the shroud ring (non-metallic, thermally stable) and the control ring (metallic, mechanically strong). This segmentation allows each component to be optimized for its specific function - the shroud ring for thermal stability and the control ring for mechanical control - while working together as an integrated system.
4Manufacturing precision
If retention springs apply strong radially inward force to maintain clearance, then clearance control is improved, but the springs experience increased stress
Solution Approach 1:
The retention springs are designed to work in conjunction with the movable control ring system. Rather than requiring extremely high spring forces to maintain clearance against a fixed structure, the springs only need to provide sufficient force to overcome the centrifugal and thermal expansion forces acting on the rotor. The control ring mechanism translates these moderate spring forces into precise radial position adjustments of the shroud ring, maintaining clearance with reduced spring stress.
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 system effectively maintains optimal tip clearance, improving engine performance by reducing thermal stress and ensuring precise positioning, thereby enhancing thermodynamic efficiency and reducing fuel consumption.
Implementation Method 1
The retention spring is engaged with the support ring radially outward from the shroud ring, and applies a radially inwardly directed force on the support ring in the troughed section
Implementation Method 2
In response to thermal excursions, the lengths of the blade tips typically vary at a different rate than that at which the static structures expand or contract
Data Source
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AI summary
A retention and control system (60) includes a rotor configured to rotate about an axis. A shroud ring (88) has a peripheral groove (108) and surrounds the rotor with a clearance (92) defined between the rotor and the ring. A support ring (96) engages the shroud ring in the peripheral groove and axially locates the shroud ring. The support ring includes a series of tabs (111-115), each with an aperture, projecting radially outward from the support ring. A retention spring (98) engages the support ring radially outward from the shroud ring and includes a series of openings, one of which registers with each of the apertures. An alignment pin (102) extends through each of the registered openings and apertures to locate the support ring and the engaged shroud ring concentrically with the turbine about the axis.