Gas Turbine Tip Clearance Control via Thermal Shrinkage
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Solution Overview
Problem
Traditional clearance control systems in gas turbine engines are large, heavy, and slow to respond, providing limited improvement in tip clearance and reducing engine efficiency due to differential thermal expansion between blade, outer air seal, and case structures.
Innovation Solution
A control system utilizing a clearance control ring with high thermal expansion coefficient, independently movable from the case structure, and air flow management to maintain optimal tip clearance through temperature-controlled air injection, allowing rapid adjustment of the outer air seal position relative to the blade.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional clearance control systems with valves and manifolds are used, then tip clearance control is achieved, but the system becomes large, heavy, and slow to respond
Solution Approach 1:
The patent extracts the essential function of tip clearance control from the complex traditional system by removing valves and manifolds. Instead, it uses a simplified carrier element with cooling channels that directly receive cooling air from the compressor, eliminating unnecessary components while maintaining the core functionality of thermal shrinkage for clearance control.
Solution Approach 2:
The patent replaces the mechanical valve-and-manifold system with a direct fluid delivery system. Cooling air is routed directly through the carrier element's internal channels, substituting complex mechanical flow control components with a streamlined thermal management approach that responds faster and weighs less.
2Manufacturing precision
If traditional clearance control systems are used, then some clearance improvement is achieved, but the response time is slow and clearance improvement is limited
Solution Approach 1:
The carrier element is pre-designed with integrated cooling channels that are ready to receive cooling air immediately when needed. This preliminary configuration eliminates the delay associated with traditional systems that must first open valves and route air through manifolds, enabling rapid thermal response when clearance adjustment is required.
Solution Approach 2:
The system dynamically adjusts tip clearance by controlling the flow of cooling air through the carrier element. By modulating the cooling air flow rate, the system can rapidly change the thermal state of the carrier element, causing it to expand or contract and thereby dynamically adjust the tip clearance to optimal values for different operating conditions.
3Adaptability or versatility
If different materials and sizes are used for blades, BOAS, and case structure, then design flexibility is improved, but differential thermal expansion causes blade rubbing or clearance increase
Solution Approach 1:
The patent applies local thermal management to the carrier element and BOAS assembly. By directing cooling air specifically to these components, the system creates localized thermal zones that can be independently controlled. This allows differential thermal expansion to be managed locally at the critical clearance interface rather than requiring uniform thermal control of the entire engine structure.
Solution Approach 2:
The patent explicitly utilizes thermal expansion principles by cooling the carrier element and BOAS with compressed air. The cooling causes these components to thermally shrink, reducing their diameter and thereby maintaining or reducing tip clearance. This controlled thermal expansion/contraction mechanism compensates for the differential thermal expansion between blades, BOAS, and case structure, preventing blade rubbing while maintaining design flexibility.
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 achieves faster thermal response and tighter high-pressure turbine clearances, improving thrust specific fuel consumption by up to 0.4% and reducing system weight and complexity compared to traditional systems.
Implementation Method 1
The control system and valve are configured to deliver flow into the internal cavity to control movement of the clearance control ring
Implementation Method 2
Since the blades, the BOAS, and the structure that support the BOAS are different sizes and/or are formed of different materials, they respond to temperature changes in different manners
Data Source
Figure 1
Figure 2A~3
Figure 4A~7
AI summary
A control system for a gas turbine engine (20) comprises a case structure (70), a clearance control ring (66) mounted for movement relative to the case structure (70), an outer air seal (64) mounted to the clearance control ring (66) and facing a first engine component (62), and a control and valve assembly (200) that receives flow from a flow input source (24). The control and valve assembly (200) is configured to direct flow into a first cavity (68) positioned radially between the case structure (70) and the outer air seal (64), and wherein the control and valve assembly (200) is configured to direct flow into a second cavity (208) positioned downstream of the first cavity (68) to interact with a second engine component (114).