Variable Nozzle Exit Area via Boundary Layer Control
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Solution Overview
Problem
Turbofan engines with fixed nozzle exit areas have limited ability to manage operational characteristics, such as fuel efficiency, due to the lack of variable parameters, which results in restricted engine performance and efficiency.
Innovation Solution
A flow control device that alters the nozzle exit area by manipulating the boundary layer within the bypass flow path using bleed air, allowing for changes in the nozzle exit area to adjust thrust and maintain efficient operation across various flight conditions without significant cost or weight penalties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the nozzle exit area is made fixed, then the engine structure is simpler and more reliable, but the engine performance and efficiency are limited due to lack of variable parameters
Solution Approach 1:
The patent applies the dynamics principle by transforming the fixed nozzle exit area into a variable one through boundary layer manipulation. By using bleed air to control the boundary layer thickness, the effective nozzle exit area becomes dynamically adjustable, allowing the engine to adapt its performance characteristics while maintaining structural simplicity and reliability.
2Productivity
If the nozzle exit area is made variable through mechanical means, then the engine performance can be optimized, but the device complexity and weight increase significantly
Solution Approach 1:
The patent replaces complex mechanical variable area control systems with a fluid-based boundary layer control system. Instead of using moving mechanical parts to change the physical nozzle geometry, the invention uses bleed air to manipulate the boundary layer, which effectively varies the nozzle exit area through aerodynamic means, thereby reducing mechanical complexity.
Solution Approach 2:
The invention employs pneumatic principles by using compressed bleed air from the engine compressor to control the boundary layer thickness. The bleed air is introduced through slots or holes in the nozzle wall, creating a pneumatic system that adjusts the effective nozzle area without mechanical movement, thus avoiding the complexity and weight of mechanical actuation systems.
3Productivity
If the boundary layer is manipulated using bleed air, then the nozzle exit area can be varied efficiently, but the engine weight and cost increase
Solution Approach 1:
The patent applies the universality principle by utilizing bleed air that is already extracted from the engine compressor for a dual purpose: first, it serves its traditional function of controlling compressor surge margins, and second, it is used to manipulate the boundary layer at the nozzle exit. This multi-functional use of bleed air allows the system to achieve variable nozzle area control without adding separate dedicated systems, thereby minimizing additional weight.
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
Enables flexible management of engine operating characteristics by varying the nozzle exit area, maintaining efficient fan operation and reducing noise levels across different flight conditions through controlled boundary layer adjustments, thereby enhancing overall engine performance.
Implementation Method 1
A flow control device provides a variable effective nozzle exit area for discharging fan bypass flow. The flow control device may be used to effectively change the nozzle exit area by altering a boundary layer within the bypass flow path.
Implementation Method 2
The flow control device may be used to effectively change the nozzle exit area by altering a boundary layer within the bypass flow path using bleed air
Data Source
Figure 1
Figure 2a~4
AI summary
A turbofan engine includes core and fan nacelles that provide a bypass flow path having a nozzle exit area. The bypass flow path carries a bypass flow to be expelled from the nozzle exit area. A turbofan is arranged within the fan nacelle and upstream from the core nacelle for generating the bypass flow. A flow control device includes a surface in the bypass flow path including an aperture. The flow device is adapted to introduce a fluid into the bypass flow path for altering a boundary layer of the bypass flow that effectively changes the nozzle exit area. In one example, bleed air is introduced through the aperture. In another example, pulses of fluid from a Helmholz resonator flow through the aperture. By decreasing the boundary layer, the nozzle exit area is effectively increased. By increasing the boundary layer, the nozzle exit area is effectively decreased.