Variable Nozzle Exit Area for Low Pressure Turbine Speed Control
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Solution Overview
Problem
Current turbofan engines are designed to accommodate maximum low pressure turbine speed, leading to increased weight and cost, and are limited by fixed area nozzles that restrict operation to a specific characteristic speed, which is rarely utilized during typical flight conditions, especially in commercial aircraft.
Innovation Solution
A turbofan engine control system that detects conditions threatening to exceed the maximum design speed of the low pressure turbine and reduces the nozzle exit area to create backpressure, thereby maintaining the speed below the maximum design speed, ensuring efficient thrust throughout the flight envelope without increasing turbine speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the low pressure turbine is designed for higher maximum speed, then the engine can provide needed thrust throughout the flight envelope, but the engine becomes heavier and more costly
Solution Approach 1:
The patent applies a variable area nozzle that can dynamically adjust its exit area based on operating conditions. This allows the engine to optimize thrust output for different flight regimes without requiring the turbine to be designed for maximum speed in all conditions, thereby reducing weight while maintaining performance capability.
Solution Approach 2:
The patent changes the nozzle exit area parameter dynamically to control turbine speed. By adjusting this parameter, the engine can operate at lower turbine speeds during conditions where maximum thrust is not required, avoiding the need to design for peak speeds and reducing overall engine weight.
2Reliability
If the low pressure turbine is designed for higher maximum speed, then the engine can accommodate maximum operating speed plus margin, but the containment system must be designed more robustly
Solution Approach 1:
The variable area nozzle dynamically adjusts to maintain turbine speed within acceptable limits, preventing the need for an overly robust containment system designed for maximum theoretical speeds. The system adapts in real-time to keep speeds within safe operating ranges.
Solution Approach 2:
The control system takes preliminary action by reducing nozzle area before turbine speed can reach dangerous levels, creating backpressure that counteracts speed increases. This preventive approach avoids the need for oversized containment structures.
3Device complexity
If fixed area nozzles are used, then the engine structure is simpler, but the ability to operate the engine to a fixed characteristic is limited
Solution Approach 1:
The patent transitions from a static fixed area nozzle to a dynamic variable area nozzle that can adjust its exit area. This adds control flexibility allowing the engine to adapt to different operating conditions and flight regimes, improving versatility while maintaining manageable complexity through automated control.
Solution Approach 2:
The variable area nozzle serves multiple functions: it controls turbine speed, optimizes thrust output, and adapts to different flight conditions. This single component provides multiple benefits that would otherwise require separate systems, balancing added complexity with functional versatility.
4Speed
If the nozzle exit area is reduced to maintain turbine speed, then the maximum design speed is avoided, but backpressure is created on the turbofan
Solution Approach 1:
The control system continuously monitors turbine speed and nozzle area, and adjusts the nozzle area in response to speed changes. This feedback mechanism allows the system to manage the trade-off between speed control and backpressure, optimizing performance by making real-time adjustments based on actual operating conditions.
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 system allows for efficient thrust generation at reduced low pressure turbine speed, balancing thrust requirements and fan stability across various flight conditions, including high altitude take-offs, without the need for excessive turbine speed, thus optimizing engine performance and reducing weight and cost.
Implementation Method 1
the nozzle exit area is reduced, which creates a backpressure on the turbofan thereby counteracting an increase in low spool speed
Data Source
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AI summary
A turbofan engine control system for managing a low pressure turbine speed is provided. The turbofan engine control system includes a low spool having a low pressure turbine that are housed in a core nacelle. The low pressure turbine is adapted to rotate at a speed and includes a maximum design speed. A turbofan is coupled to the low spool. A fan nacelle surrounds the turbofan and core nacelle and provides a bypass flow path. The bypass flow path includes a nozzle exit area. A controller is programmed to command a flow control device adapted to effectively decrease the nozzle exit area in response to a condition. Reducing the nozzle exit area, either physically or otherwise, maintains the speed below the maximum design speed.