Turbofan Nozzle Exit Area Control for Fan Operability
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Solution Overview
Problem
Turbofan engines face design challenges and performance penalties in managing fan operability margins across varying flight conditions, leading to inefficient fuel consumption and compromised performance.
Innovation Solution
A turbofan engine control system that dynamically adjusts the nozzle exit area using a flow control device, responsive to airspeed and throttle position, to optimize fan operability and reduce unnecessary margins, thereby improving efficiency and fuel consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed nozzle exit area is used, then the engine structure is simple, but the fan operability margin is insufficient and fuel consumption increases
Solution Approach 1:
The nozzle exit area is made dynamically adjustable through a flow control device that can change the nozzle geometry in response to varying flight conditions. This allows the engine to optimize the fan operating line by adjusting the nozzle exit area to match current operational requirements, thereby reducing fuel consumption while maintaining adequate fan operability margin across different speeds and throttle positions.
Solution Approach 2:
The physical size of the nozzle exit area is changed as a variable parameter to optimize engine performance. By manipulating the nozzle exit area parameter in response to airspeed and throttle position, the system achieves the target operability line and improves fuel efficiency without compromising fan operability.
2Use of energy by moving object
If the nozzle exit area is decreased to improve fuel consumption, then the fan operability margin is reduced, but this creates unstable operation
Solution Approach 1:
The flow control device is controlled by a controller that receives feedback about engine operating conditions including airspeed and throttle position. This feedback mechanism ensures that the nozzle exit area is adjusted to the optimal value that maintains adequate fan operability margin while minimizing fuel consumption, preventing operation near unstable boundaries.
Solution Approach 2:
The system dynamically adjusts the nozzle exit area based on real-time operating conditions, allowing the engine to operate at optimal points across the flight envelope rather than being constrained by a fixed nozzle design. This dynamic adjustment maintains reliability while improving efficiency.
3Reliability
If the engine is designed to meet fan operability requirements throughout the flight envelope, then fan stability is maintained, but performance penalties occur and fuel consumption increases
Solution Approach 1:
The nozzle exit area is made dynamically adjustable to match varying flight conditions. This allows the engine to optimize performance at each operating point rather than being designed for worst-case scenarios across the entire flight envelope, thereby eliminating performance penalties while maintaining fan operability through active control.
Solution Approach 2:
By changing the nozzle exit area parameter in response to operating conditions, the engine achieves optimal performance characteristics at each point in the flight envelope. This parameter adjustment allows the system to meet fan operability requirements without the performance penalties associated with fixed nozzle designs.
Data Source
AI summary
(A1) A turbofan engine (10) is provided that includes a spool (14). The spool (14) supports a turbine (18) and is housed within a core nacelle (12). A fan (20) is coupled to the spool (14) and includes a target operability line. The target operability line provides desired fuel consumption, engine performance, and/or fan operability margin. A fan nacelle (34) surrounds the fan (20) and core nacelle (12) to provide a bypass flow path (39) having a nozzle exit area (40). A controller (50) is programmed to command a flow control device (41) for changing the nozzle exit area (40). The change in nozzle exit area (40) achieves the target operability line in response to an engine operating condition that is a function of airspeed and throttle position. A change in the nozzle exit area (40) is used to move the operating line toward a fan stall or flutter boundary by manipulating the fan pressure ratio.