Gas Turbine Casing Thermal Expansion Control
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Solution Overview
Problem
Existing gas turbine engine designs face challenges in maintaining optimal rotor tip clearance during step climb accelerations, leading to increased cruise specific fuel consumption due to inadequate casing radial growth, which results in blade tip rub and suboptimal clearance settings.
Innovation Solution
The implementation of closable ducts that vary the heat transfer condition on the internal surface of the casing by diverting hot cooling air into a heating control chamber, allowing for rapid expansion of the casing during step climb accelerations by either increasing or reducing internal heat transfer, thereby reducing the need for external cooling and tightening the cruise clearance gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If external cooling air is blown on the casing to reduce temperature and achieve tip clearance control, then the running tip clearance is reduced, but the response time during step climb acceleration is insufficient leading to blade tip rub
Solution Approach 1:
The patent pre-positions hot cooling air in a heating control chamber adjacent to the casing during normal operation. When step climb acceleration is detected, this pre-positioned hot air is rapidly directed onto the casing through controllable flow paths, providing immediate thermal expansion before blade tip rub can occur. This preliminary positioning of thermal energy resolves the contradiction by enabling fast response without requiring external cooling system adjustments.
Solution Approach 2:
The patent implements dynamic control of air flow paths using controllable valves or dampers that adjust the distribution of cooling air between the external cooling manifold and the internal heating control chamber based on operating conditions. During acceleration, the system dynamically redirects hot air internally; during steady state, external cooling dominates. This dynamic adaptability resolves the contradiction between precise clearance control and rapid response time.
2Adaptability or versatility
If modulated valve is used to control external TCC flow, then any flow level from zero to fully-open can be achieved, but the step climb acceleration effect cannot be compensated leading to suboptimal cruise clearance
Solution Approach 1:
The patent segments the cooling air flow control into two independent pathways: an external cooling manifold for steady-state clearance control and an internal heating control chamber for transient acceleration compensation. Each pathway can be independently modulated, allowing the external valve to optimize cruise clearance while the internal chamber handles step climb effects. This segmentation resolves the contradiction by separating the two conflicting control objectives into independent controllable systems.
Solution Approach 2:
The patent introduces an intermediary heating control chamber that acts as a mediator between the cooling air supply and the casing. This chamber stores hot cooling air and releases it strategically during acceleration events, mediating between the external cooling system's steady-state control and the casing's transient thermal response requirements. This intermediary resolves the contradiction by providing an additional control degree of freedom that addresses step climb effects without compromising cruise optimization.
3Temperature
If heat shield is positioned to reduce heat transfer from hot side air flow to casing, then casing temperature is reduced, but rapid casing expansion during step climb cannot be achieved
Solution Approach 1:
The patent pre-positions hot cooling air in the heating control chamber adjacent to the casing, ready to be rapidly discharged onto the casing surface during acceleration. This preliminary positioning of thermal energy source eliminates the need for gradual heat transfer through shields, enabling immediate casing expansion when needed. The principle resolves the contradiction by providing rapid thermal actuation without relying on slow conductive heat transfer through heat shields.
Solution Approach 2:
The patent extracts the hot cooling air from the main cooling flow path and positions it separately in the heating control chamber, removing it from the gradual heat transfer process that occurs through heat shields. This extracted hot air can be rapidly deployed directly onto the casing when acceleration is detected, achieving fast thermal expansion independent of heat shield limitations. This extraction resolves the contradiction by decoupling steady-state temperature control from transient expansion requirements.
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 approach enables rapid casing expansion during step climb, tightening cruise clearances and reducing specific fuel consumption by leveraging existing high-pressure air for efficient heat transfer, with minimal hardware changes and simplified control systems.
Implementation Method 1
hot cooling air flows through the through-holes to impinge on the casing
Implementation Method 2
enables rapid casing expansion during step climb
Implementation Method 3
blowing relatively cool, low pressure air on to the outer surface of the casing, thereby reducing its temperature and, because it is a circumferentially continuous component, producing a radial contraction of the casing
Data Source
Figure 1
Figure 2~3
Figure 4(a)~5
AI summary
A gas turbine engine and a method of operating the gas turbine engine is provided. The gas turbine engine has a row of circumferentially spaced rotor blades (32), each having a radially outer tip. The engine further has a plurality of seal segments (33) circumscribing the rotor blade tips and attached to a radially inward side of a casing (1) of the engine. The seal segments are spaced from the casing by a spacing cavity (B). In use, a flow of relatively hot cooling air is routed to the spacing cavity to provide cooling for the seal segments. The engine further has an external cooling arrangement for impinging relatively cold cooling air on a radially outward side of the casing and thereby controlling a radial clearance (G) between the rotor blade tips and the seal segments. The engine further has a wall (39) containing a plurality of through-holes (40) which is attached to a radially inward side of the casing adjacent the seal segments. The wall is spaced from the casing to define a heating control chamber (E) between the wall and the casing. The engine further has one or more closable ducts (41) which allow air to be exhausted from the heating control chamber. When the ducts are open, a portion of the hot cooling air flows through the through-holes to impinge on the casing and then exhausts from the heating control chamber through the ducts.