Gas Turbine Casing Heating Reduces Lockout Time
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Solution Overview
Problem
Gas turbine engines face a lockout condition after hot shutdown, where rapid cooling and thermal expansion cause the rotor to become locked with the casing, necessitating a restart within minutes to prevent damage and resulting in an undesirable downtime.
Innovation Solution
The method involves heating the casing or cooling the rotor after a hot shutdown to increase radial clearances, using heating elements or airflow to reverse thermomechanical changes, thereby reducing the lockout period. This includes selectively heating the casing with resistance heating elements or using a blower to circulate ambient air and equalize temperatures around the rotor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the engine is shut down immediately without gradually reducing power level, then operational requirements are met, but the rotor and casing contact each other causing lockout condition
Solution Approach 1:
The system performs preliminary action by heating the casing or cooling the rotor immediately after shutdown to prevent the thermomechanical changes that would otherwise cause rotor lockout. This anticipates and counteracts the thermal contraction and rotor bowing that occur during rapid cooling, allowing immediate restart without lockout conditions.
Solution Approach 2:
The invention changes the thermal parameters of the system by actively heating the casing or cooling the rotor after shutdown. This reverses the natural thermomechanical response to hot shutdown, maintaining radial clearances and preventing rotor-casing contact that would otherwise occur during rapid cooling.
2Temperature
If the rotor is allowed to cool naturally after shutdown, then cooling process occurs, but radial clearance decreases causing rotor to lock with casing
Solution Approach 1:
Instead of allowing natural cooling that reduces radial clearance, the system inverts the approach by actively heating the casing or cooling the rotor. This reverses the thermal gradient and expansion/contraction behavior, maintaining or increasing radial clearance during the shutdown period.
Solution Approach 2:
The invention utilizes thermal expansion principles by heating the casing to expand it outward, increasing radial clearance. Alternatively, cooling the rotor causes it to contract, also increasing clearance. Both approaches apply controlled thermal changes to prevent the harmful clearance reduction that occurs during natural cooling.
3Loss of time
If heating elements or airflow systems are added to reduce lockout time, then lockout period is reduced, but device complexity increases
Solution Approach 1:
The system achieves multi-functionality by using components that serve both operational and lockout prevention functions. For example, the casing heating elements can serve both as thermal management components during operation and as lockout prevention mechanisms after shutdown. Similarly, airflow systems can provide both cooling during operation and clearance maintenance during shutdown.
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 proposed method significantly reduces the lockout time from hours to minutes, potentially eliminating it entirely, allowing for quicker engine restarts and reducing the risk of rotor and casing damage.
Implementation Method 1
heating the casing of the engine so as to expand the casing and increase a radial clearance between the blades of the rotor and the casing
Implementation Method 2
heating the casing of the engine so as to expand the casing and increase a radial clearance between the blades of the rotor and the casing
Implementation Method 3
pumping an airflow of ambient air into the inlet and allowing the pumped air to flow through the casing, past the rotor, and out the exhaust duct, so as to reverse at least partially, the thermomechanical changes
Data Source
AI summary
A method is provided of reducing lockout time of a gas turbine engine which includes: an inlet, a compressor, a combustor, a turbine, and an exhaust duct, where the compressor and the turbine are carried on a turbomachinery rotor and each include an array of blades mounted for rotation inside a casing of the engine. The method includes: operating the engine at a first power output; shutting down operation of the engine without substantially reducing the power output beforehand, wherein thermomechanical changes occur in the engine subsequent to shutdown that tend to reduce a radial clearance between at least one of the blades and the casing; and subsequent to shutting down the engine, (1) heating the casing and/or (2) pumping an airflow of ambient air into the inlet and through the casing, past the rotor, and out the exhaust duct, so as to reverse at least partially the thermomechanical changes.