Active Clearance Control in Gas Turbine Engines
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Solution Overview
Problem
Gas turbine engines face efficiency losses due to leakage of combustion gases through blade tip gaps and thermal expansion differences between turbine blades and shrouds, which require a large initial clearance to prevent rubbing but decrease efficiency.
Innovation Solution
A compound active clearance control system using a heat exchanger to cool compressor discharge air, which is then distributed to control blade tip clearance by heating or cooling the turbine case and blades, allowing for precise adjustment of radial clearance through a network of valves and an impingement baffle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large initial blade tip clearance is set to prevent blade tip rubbing during thermal expansion, then reliability is improved, but efficiency deteriorates due to increased combustion gas leakage
Solution Approach 1:
The patent implements active clearance control that dynamically adjusts blade tip clearance during engine operation. The system uses thermal response elements (heat exchangers) that can be heated or cooled to actively control the radial position of turbine shrouds, maintaining optimal clearance dynamically rather than relying on a fixed large initial clearance. This resolves the contradiction by making clearance adaptive to operating conditions.
Solution Approach 2:
The system changes the temperature parameter of the turbine case and shrouds to control thermal expansion/contraction. By controlling the temperature of structural components through heated or cooled thermal response elements, the system adjusts the physical dimensions of shrouds to maintain optimal blade tip clearance, thereby reducing leakage while preventing rubbing.
2Reliability
If compressor bleed air is used for turbine cooling and active clearance control, then reliability and efficiency are improved, but energy loss increases due to air being bled from the combustion cycle
Solution Approach 1:
The patent makes compressor discharge air serve multiple functions simultaneously. The same air stream is used for both turbine blade cooling (through internal cooling passages) and for active clearance control (through external heat exchangers on the turbine case). This multi-functional use reduces the total amount of air that needs to be bled from the combustion cycle, thereby reducing energy loss while maintaining both blade protection and clearance control.
Solution Approach 2:
The system merges the previously separate cooling and clearance control air supply systems into a single integrated system. Both functions now draw from the same compressor discharge air source, which is optimally positioned and temperature-controlled, improving overall system efficiency while reducing the parasitic drag on the combustion cycle.
3Loss of energy
If conventional active clearance control is used during cruise operation, then efficiency is improved, but the system cannot adequately handle transient reburst conditions without requiring large nominal clearance
Solution Approach 1:
The patent implements a dynamic clearance control system that can respond to transient conditions. The thermal response elements (heat exchangers) mounted on the turbine case can be rapidly heated or cooled to adjust shroud position in real-time, allowing the system to adapt to transient reburst conditions while maintaining optimal clearance during steady-state cruise operation. This dynamic capability enables the system to handle both cruise efficiency and transient adaptability.
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 system significantly enhances engine efficiency and reduces specific fuel consumption by minimizing blade tip clearance, allowing for smaller nominal clearances without risk of rubbing, and synergistically uses compressor discharge air for both clearance control and blade cooling.
Implementation Method 1
A heat exchanger is used for cooling pressurized air bled from the compressor
Implementation Method 2
the turbine components thermally expand and contract which correspondingly affects the size of the blade tip clearance
Implementation Method 3
A distribution network joins the heat exchanger to the turbine for selectively channeling air from the heat exchanger below the blades and above the shroud for controlling blade tip clearance
Data Source
AI summary
A gas turbine engine includes a compressor, combustor, and turbine having a row of blades mounted inside a surrounding turbine shroud. A heat exchanger is used for cooling pressurized air bled from the compressor. A distribution network joins the heat exchanger to the turbine for selectively channeling air from the heat exchanger below the blades and above the shroud for controlling blade tip clearance.