Passive Blade Tip Clearance Control via Thermal Expansion
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Solution Overview
Problem
Gas turbine engines face inefficiencies due to excessive contact between rotating blades and blade tracks, and inadequate clearance management, which leads to degradation and performance losses.
Innovation Solution
A passive blade tip clearance control system that uses pressurized bleed air to heat or cool the inner case, controlling the blade tip clearance gap without active control devices, by sealing a cavity between the outer and inner cases and utilizing turbulators for enhanced heat transfer, allowing the system to adjust based on engine operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If clearance between rotating blades and blade track is reduced to improve efficiency, then engine efficiency is improved, but blade degradation and contact damage occur
Solution Approach 1:
The patent changes the temperature parameter of the case structure using bleed air heating. By controlling the temperature of the case, the thermal expansion of the case is adjusted, which in turn controls the clearance between the rotating blades and blade track. This allows maintaining small clearance for efficiency while preventing blade contact and degradation.
Solution Approach 2:
The patent directly utilizes thermal expansion of the case structure. Bleed air is directed to heat the case, causing it to expand thermally. This thermal expansion adjusts the radial position of the blade track, thereby controlling the clearance gap. The system exploits the natural thermal expansion property to achieve active clearance control without mechanical actuators.
2Manufacturing precision
If active control devices are used to manage blade tip clearance, then clearance control precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces mechanical active control devices (such as actuators, valves, and sensors) with a thermal field-based control mechanism. Bleed air is used to create thermal gradients that drive case expansion, which passively controls clearance. This substitution eliminates complex mechanical control systems while achieving precise clearance management through thermal fields.
Solution Approach 2:
The system uses the engine's own bleed air as the control medium, making the control system self-sufficient. The thermal energy from bleed air naturally drives the case expansion, and the system automatically adjusts clearance based on operating conditions without requiring external control inputs or active intervention.
3Length of moving object
If case temperature is increased to control clearance, then blade tip clearance is reduced, but energy loss increases
Solution Approach 1:
The patent recovers and utilizes bleed air that would otherwise be discarded or underutilized. By directing this thermal energy to heat the case and control clearance, the system converts a potential energy loss into a useful control function. This recovery approach reduces overall energy waste while achieving clearance control.
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 solution effectively manages blade tip clearance, improving engine efficiency by matching thermal growth of components and avoiding contact issues, thereby enhancing performance and reducing degradation without the need for active control systems or valves.
Implementation Method 1
The cavity is configured to receive the bleed air from the compressor to drive movement of the inner case radially inward or outward depending on operating conditions
Implementation Method 2
heating the shroud-ring support 34 during start-up opens the gap 36 to accommodate the faster change in diameter of the turbine wheel 24
Implementation Method 3
the inner case includes a plurality of turbulators coupled to an upper surface of the inner case within the cavity radially outward of the second turbine blade stage to increase heat transfer between the pressurized bleed air and the inner case
Data Source
Figure 1~2
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AI summary
The present disclosure relates to a gas turbine engine (10) including a turbine wheel (24) mounted for rotation about a central reference axis (11) and a turbine shroud ring (26) mounted radially outward from the turbine wheel (24). The turbine wheel (24) includes a plurality of blades (30) that are spaced apart radially from the turbine shroud ring (26) to establish a blade tip clearance gap (36). The gas turbine engine (10) further includes a blade tip clearance control system (40) that passively controls the size of the blade tip clearance gap (36) based on engine operation, the clearance control system (40) comprising a shroud-ring support (34) coupled to the variable-diameter turbine shroud ring (26) that is configured to drive motion of the variable-diameter turbine shroud ring (26) radially inward or outward based on temperature of the shroud-ring support (34) and defining at least in part a cavity (50) located radially outward of the variable-diameter turbine shroud ring (26), wherein the cavity (50) is fluidly coupled to a bleed-air passageway (46) that extends from the compressor (14) to the cavity (50) without interruption from a valve and to a cooling-air passageway (47) that extends from the cavity (50) to the low-pressure section (22) such that pressurized bleed air from the compressor (14) is conducted to the cavity (50) of the passive blade tip clearance control system (40) so that the temperature and motion of the shroud-ring support (34) is controlled based on the operating conditions of the gas turbine engine (10) without active control of the pressurized bleed air provided to the cavity (50).