Jet Engine Nozzle Projections for Noise Reduction
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Solution Overview
Problem
Aircraft engines continue to pose a significant noise challenge due to their contribution to overall aircraft noise, despite advancements in high bypass ratio engines, necessitating further reduction in engine noise to meet stringent noise certification rules.
Innovation Solution
The implementation of jet engine nozzle exit configurations with circumferentially varying projections, such as chevrons, that change in geometric features like length, angular deflection, and density around the perimeter to enhance mixing with freestream air, thereby reducing noise levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If chevrons are added to the nozzle exit to increase mixing between engine flow and freestream air, then noise reduction is achieved, but device complexity increases
Solution Approach 1:
The nozzle exit perimeter is segmented into multiple discrete projections (chevrons) rather than using a continuous structure. These projections are circumferentially spaced and can be independently configured, allowing the noise reduction function to be distributed across multiple simple elements rather than one complex continuous structure.
Solution Approach 2:
The geometric features of the projections vary locally around the perimeter - specifically, the length of successive projections decreases in a direction away from the aircraft wing. This local variation optimizes noise reduction in different directions while maintaining overall system simplicity.
2Object-affected harmful factors
If the geometric features of projections are varied circumferentially to optimize noise reduction in specific directions, then noise reduction effectiveness improves, but manufacturing precision requirements increase
Solution Approach 1:
The projections exhibit asymmetric geometric features around the perimeter, with lengths that systematically vary in relation to the aircraft wing position. This asymmetric configuration targets noise reduction toward specific directions (away from the wing) while accepting simpler manufacturing for the systematic variation pattern.
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 approach effectively reduces engine noise by increasing mixing between the engine flow and surrounding air, achieving noise reductions of up to 5 dB at low frequencies and 1.5 dB in the far field, while maintaining thrust levels, thus meeting community noise standards.
Implementation Method 1
increase the amount of mixing between the high velocity gases exiting the engine, and the surrounding freestream air
Implementation Method 2
enhance mixing with freestream air, thereby reducing noise levels
Data Source
AI summary
Nozzle exit configurations and associated systems and methods are disclosed. An aircraft system in accordance with one embodiment includes a jet engine exhaust nozzle having an internal flow surface and an exit aperture, with the exit aperture having a perimeter that includes multiple projections extending in an aft direction. Aft portions of individual neighboring projections are spaced apart from each other by a gap, and a geometric feature of the multiple can change in a monotonic manner along at least a portion of the perimeter.