Active High Pressure Turbine Clearance Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current gas turbine engines face challenges in maintaining optimal clearance between turbine blades and outer airseals during engine transients due to the faster centrifugal growth of blades compared to the thermal control dynamics, leading to potential rub conditions and sub-optimal fuel efficiency.
Innovation Solution
The method involves modulating fuel flow and using variable pitch stator vanes to control the acceleration rate of the high pressure turbine rotor, reducing the risk of rub conditions by adjusting the clearance gap, and compensating with increased low pressure turbine acceleration to maintain optimal clearance levels during engine acceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermal control methods are used to regulate clearance, then fuel burn and efficiency improve, but the response speed is too slow for engine transients
Solution Approach 1:
The system dynamically switches between two control modes (thermal control mode for steady-state and mechanical control mode for transients) based on operating conditions. The mechanical control mode uses variable pitch stator vanes to actively control rotor acceleration and clearance during transients, while thermal control mode uses bypass airflow for steady-state clearance optimization, achieving both fast response and precision.
Solution Approach 2:
The system changes the control parameter from thermal (bypass airflow temperature/flow) to mechanical (stator vane pitch angle, rotor acceleration rate) based on operating regime. This parameter switching enables the system to address the speed-precision contradiction by using mechanical parameters for fast transient response and thermal parameters for precise steady-state control.
2Loss of energy
If tighter clearance target is used during cruise, then fuel burn and efficiency benefit increase, but risk of rub conditions during transients increases
Solution Approach 1:
The system performs preliminary action by reducing rotor acceleration rate during transient phases before reaching cruise operating conditions. The variable pitch stator vanes are adjusted in advance to control the rate of clearance reduction, preventing rub conditions from developing during acceleration while still allowing tighter clearance targets to be achieved during steady-state cruise operation.
Solution Approach 2:
The system dynamically adjusts the clearance control strategy based on operating phase. During transients, mechanical control mode limits rotor acceleration to prevent rubs. During cruise, thermal control mode enables tighter clearance targets for optimal fuel efficiency. This dynamic switching resolves the contradiction between fuel efficiency and reliability.
3Productivity
If rotor acceleration rate is increased, then engine response time improves, but centrifugal growth of blades increases clearance pinch
Solution Approach 1:
The variable pitch stator vanes act as an intermediary mechanism between the fuel flow and rotor acceleration. By adjusting the stator vane pitch angle, the system mediates the relationship between fuel input and rotor speed increase, controlling the acceleration rate to prevent excessive centrifugal blade growth while maintaining acceptable engine response performance.
Solution Approach 2:
The system changes the acceleration control parameter from unrestricted fuel-driven acceleration to controlled stator vane-pitch-limited acceleration. This parameter change enables the system to manage blade centrifugal growth during transients while maintaining productive engine response capability through coordinated control of multiple parameters.
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 allows for tighter clearance control during engine transients, reducing the risk of rub conditions and improving fuel efficiency and hot-section life by maintaining optimal clearance levels throughout the engine's operating envelope.
Implementation Method 1
The potential clearance pinch during an engine acceleration is largely a result of the centripetal growth of the blades, a mechanical phenomenon from the rate of high spool rotor speed (N2) acceleration.
Implementation Method 2
Due to the slow nature of the thermal transients through which the clearances are controlled, relative to the acceleration capabilities of the engine
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention relates to a method of operating a gas turbine engine (20) for actively controlling the clearances in the high-pressure turbine section, wherein the variable-pitch stator vanes are controlled to reduce rotational speed of the high-pressure shaft in response to an acceleration command of the gas turbine engine. The variable pitch high pressure compressor vanes (76) are moved toward an open position thereby reducing an acceleration rate of a high pressure turbine rotor (60) thereby reducing a change in a clearance gap (64) between the high pressure turbine rotor and a blade outer air seal (66). By providing a variable-pitch stator vane control in addition to a fluid-based clearance control, the clearance can be controlled more accurately particularly during sharp acceleration of the gas turbine engine.