Jet Engine Noise Reduction via Pulsed Fluid Jets
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Solution Overview
Problem
Aircraft jet engines generate significant noise during takeoff due to high-speed gas streams, and existing noise reduction methods require continuous fluid supply from the engine or an external source, which can reduce engine output and are not effective across the full frequency spectrum.
Innovation Solution
A noise reduction system for aircraft jet engines featuring a nozzle with upstream recesses divided into chambers, connected to piezoelectric deformable membranes that modulate fluid jets to interact with the gas stream, allowing for pulsation at frequencies three times greater than the basic frequency, using either ambient air or compressed air, to reduce noise without continuous fluid supply from the engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If continuous fluid injection is used to reduce noise, then noise reduction effectiveness is improved, but engine output is reduced due to continuous fluid supply requirement
Solution Approach 1:
The patent implements periodic pulsed jets instead of continuous fluid injection. The system uses a pulsation mechanism that periodically ejects fluid jets at frequencies three times greater than the basic frequency of the gas stream. This periodic action achieves effective noise reduction across the full frequency spectrum while requiring less continuous fluid supply, thereby maintaining engine output.
2Object-affected harmful factors
If high-frequency pulsation is used to reduce noise across full spectrum, then noise reduction effectiveness is improved, but device complexity increases
Solution Approach 1:
The patent divides the recess into multiple chambers (first chamber, second chamber, third chamber) with piezoelectric membranes in each. This segmentation allows independent control of each chamber's pulsation, enabling high-frequency pulsed jets across the full frequency spectrum while distributing the complexity across modular components rather than requiring a single complex mechanism.
Solution Approach 2:
The patent replaces complex mechanical pulsation mechanisms with piezoelectric membranes that can be directly actuated by electrical signals. This substitution of mechanical systems with piezoelectric actuation simplifies the device while enabling precise high-frequency pulsation control across the full frequency spectrum for effective noise reduction.
3Use of energy by moving object
If piezoelectric membranes are used to vary recess volume, then energy consumption is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses thin piezoelectric membranes to form the walls of the chambers. These flexible thin films can dynamically vary the volume of each chamber in response to electrical signals, enabling energy-efficient pulsed jet generation. The thin membrane design allows for precise volume control while minimizing the material required and reducing overall device mass.
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
The system effectively reduces noise by pulsating fluid jets at higher frequencies, consuming less energy and maintaining engine performance, with the ability to modulate jet speed and reduce noise across a broader frequency range without relying on continuous fluid supply from the engine.
Implementation Method 1
The pulsation method or methods comprise in particular a piezoelectric device which is able to cause the volume of the recess or recesses filled with fluid to vary. According to one characteristic, the piezoelectric device for volume variation comprises at least one piezoelectric deformable membrane disposed in the said at least one recess.
Implementation Method 2
These jets form a triangle of interaction with the stream. It has been shown that in order to reduce the noise coming from the engine in the full spectrum of frequencies, it is necessary to pulse a jet with an excitation frequency three times greater than the basic frequency of the gas stream.
Data Source
AI summary
An aircraft jet engine comprising a nozzle to eject a gas stream, and a system for reducing the noise generated by the ejection of the gas stream. This system comprises several ducts which each are connected upstream to a recess divided into several chambers and open, downstream, at the outlet of nozzle. In this way, each duct ejects a fluid jet deriving from the recess and which interacts with the gas stream of the engine. The system also comprises a pulsation means for the fluid jet which brings about its ejection at the nozzle outlet and/or modulates its speed by varying the volume contained in the recess.