Translating Outer Cowl Modulates Third Stream Bypass Flow
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Solution Overview
Problem
Modern aircraft engines face a conflict between fuel efficiency and high specific thrust, as high-performing engines are less efficient and highly efficient engines lack thrust capabilities, leading to a trade-off in design objectives for military and commercial aircraft.
Innovation Solution
A flow control device for a turbofan engine with a third stream bypass passage, dynamically regulated by a translating outer cowl, allows for independent modulation of airflow streams to achieve high-performance or high-efficiency modes by controlling the flow through the third stream bypass passage, which interacts with the core and bypass flows to optimize thrust and fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a traditional turbofan engine architecture is used, then fuel efficiency is improved through high-bypass design, but specific thrust capability deteriorates
Solution Approach 1:
The engine architecture is segmented into three independent airflow streams: core flow, inner bypass flow, and outer bypass flow. Each stream can be independently controlled through separate flow control devices, allowing the engine to optimize the contribution of each stream to thrust generation based on operating conditions, thereby achieving both high fuel efficiency and high specific thrust capability
Solution Approach 2:
The flow control devices are designed to be dynamically adjustable during flight, enabling real-time modulation of each bypass stream's flow rate. This dynamic control allows the engine to transition between high-efficiency cruise mode (with both bypass streams active) and high-thrust maneuver mode (with adjusted stream distribution), resolving the static trade-off between fuel efficiency and thrust capability
2Adaptability or versatility
If a third stream bypass passage is added to provide independent flow modulation, then thrust and efficiency optimization is improved, but device complexity increases
Solution Approach 1:
The third stream bypass passage is nested within the existing two-stream bypass architecture, with the outer bypass passage surrounding the inner bypass passage, which in turn surrounds the core flow passage. This nested configuration allows independent control of each stream while minimizing additional structural complexity by utilizing the existing radial space arrangement
Solution Approach 2:
The flow control devices are designed with multi-functionality to manage multiple airflow streams simultaneously. Each flow control device can regulate its respective bypass stream while also influencing overall engine performance characteristics, reducing the need for separate dedicated control mechanisms for each function and thereby limiting the increase in device complexity
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 the turbofan engine to operate in high-performance or high-efficiency modes by dynamically adjusting the airflow, providing additional thrust when needed and reducing fuel consumption, thus addressing the trade-off between engine performance and efficiency.
Implementation Method 1
a third axially extending flow control surface that is radially offset from the first flow control surface and capable of axially translating with respect to the first and second flow control surfaces for modifying the gas flow path and selectively closing the flow path exit
Implementation Method 2
delivering air to a core flow path, a bypass flow path and a third stream flow path using a fan
Implementation Method 3
allowing fluid flowing through the third stream bypass passage to provide thrust to the turbofan engine
Data Source
AI summary
A flow control device includes a first axially extending flow control surface, a second axially extending flow control surface radially offset from the first surface to define a gas flow path therebetween, the gas flow path having a downstream flow path exit, and a third axially extending flow control surface radially offset from the first surface and capable of axially translating with respect to the first and second surfaces for modifying the gas flow path and selectively closing the flow path exit. A turbofan engine includes a core flow passage, a fan bypass passage located radially outward from the core flow passage, a third stream bypass passage located radially outward from the fan bypass passage, and a flow control device that dynamically regulates the third stream bypass passage, allowing fluid flowing through the third stream bypass passage to provide thrust to the turbofan engine and reduce afterbody drag.