Mixer Duct Shell for Turbofan Noise and Heat Reduction
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Solution Overview
Problem
Conventional aircraft turbofan engines emit significant noise and heat plumes that radiate unabated, causing community disturbance and increasing susceptibility to heat-seeking missiles, as these emissions are reflected off aircraft wings and pylons.
Innovation Solution
The implementation of a mixer duct system within the turbofan engine assembly, where a mixer duct shell is coaxial with the fan exhaust duct and core engine, routing a portion of fan exhaust through the mixer duct and another portion over the outer surface of the mixer duct shell, to mix and redirect exhaust gases, thereby reducing noise and heat radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional aircraft engines are installed beneath the wings, then the engine exhaust noise and heat plumes radiate unabated to nearby communities, but this configuration is simple and commonly used
Solution Approach 1:
The mixer duct is nested within the existing engine assembly structure, with the mixer duct shell positioned inside the nacelle and extending into the fan exhaust duct. This nested configuration allows the noise and heat reduction function to be integrated within the existing engine structure without requiring external additions, thus reducing harmful radiations while maintaining structural simplicity.
Solution Approach 2:
The mixer duct acts as an intermediary device between the fan exhaust and the core engine exhaust. It introduces a portion of fan exhaust through the mixer duct to mix with core exhaust, thereby reducing the temperature and noise of the combined exhaust plume before it exits the engine, effectively mitigating harmful radiations.
2Object-affected harmful factors
If a mixer duct system is implemented to reduce noise and heat radiation, then harmful emissions are reduced, but the device complexity increases
Solution Approach 1:
The mixer duct system is segmented into distinct functional zones: the mixer duct shell extending into the fan exhaust duct, the mixing region where fan and core exhaust combine, and the exit region where the mixed plume is discharged. This segmentation allows each zone to perform its specific function efficiently while keeping the overall structure manageable and maintainable.
Solution Approach 2:
The mixer duct structure serves multiple functions simultaneously: it directs fan exhaust through the mixer duct for mixing, provides structural support within the nacelle, and helps control the direction and characteristics of the exhaust plume exit. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
3Object-affected harmful factors
If fan exhaust is routed through the mixer duct for mixing, then noise and heat are reduced, but maintenance access becomes more difficult
Solution Approach 1:
The mixer duct shell is designed with movable or adjustable sections that can be positioned to facilitate maintenance access. During normal operation, the mixer duct maintains its configuration for optimal mixing performance. During maintenance, the duct can be repositioned or opened to provide access to underlying engine components, thus balancing performance with ease of repair.
4Manufacturing precision
If the mixer duct shell extends forwardly into the fan exhaust duct, then mixing effectiveness is improved, but the length of the nacelle increases
Solution Approach 1:
The mixer duct shell extends only partially into the fan exhaust duct, just enough to achieve effective mixing of fan and core exhaust. Rather than extending the full length of the duct, the mixer shell is positioned at the optimal location where mixing begins, providing sufficient mixing effectiveness while minimizing the increase in nacelle length.
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 solution effectively reduces jet noise and plume heat radiation, decreasing community disturbance and missile detection, while maintaining thrust reverser effectiveness and enabling easier maintenance access.
Implementation Method 1
A first portion of fan exhaust is routed through an interstitial mixer duct formed between an inner surface of a mixer duct shell and a core engine of the assembly
Data Source
AI summary
An aircraft includes at least one turbofan engine assembly having a shrouded core engine, a short nacelle surrounding a fan and a forward portion of the core engine, and a fan exhaust duct through the nacelle. A mixer duct shell is positioned substantially coaxial with the engine shroud and extends forwardly into the fan duct to provide an interstitial mixer duct between the mixer duct shell and the core engine shroud. The aft portion of the mixer duct shell extends over a turbine exhaust frame, an attached mixer (if included), and a tail cone exhaust plug. The mixer duct shell can reduce noise and plume exhaust heat radiated from aircraft turbofan engines.