Acoustic Panel With In-Plane Channels For Noise Attenuation
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Solution Overview
Problem
Conventional acoustic panels for aircraft propulsion units are ineffective in attenuating noise from new generation turbomachines with reduced rotation speed and vane count, leading to increased bulk and mass due to the need for thicker panels to accommodate lower frequency noise, which is undesirable for airborne applications.
Innovation Solution
The acoustic panel features a honeycomb core with an entry layer comprising plates with through-holes and grooves that form channels extending parallel to the panel, allowing frequency tuning by modifying the dimensions of the grooves without increasing the panel's thickness, thus reducing the bulk and mass dependence on the frequency of acoustic waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the acoustic panel is increased to attenuate lower frequency noise, then the acoustic attenuation performance is improved, but the bulk and mass of the panel increase significantly
Solution Approach 1:
The patent changes the orientation of the necks from perpendicular to the plate to parallel to the plate. This dimensional reorientation allows the neck length to be extended along the plate surface rather than through the thickness direction, enabling frequency tuning for lower frequencies without increasing panel thickness. The necks now extend in the plane of the panel rather than through it, decoupling frequency adjustment from thickness increase.
Solution Approach 2:
The patent modifies the geometric parameters of the necks by changing their orientation and extension direction. Instead of increasing neck length through thickness (which would increase mass), the necks are configured to extend parallel to the plate with their length measured along the plate surface. This parameter change allows independent control of acoustic frequency response from panel thickness.
2Reliability
If the thickness of the acoustic panel is increased to attenuate lower frequency noise, then the acoustic attenuation performance is improved, but the bulk of the panel increases
Solution Approach 1:
The patent reorients the neck configuration from thickness-direction extension to in-plane extension. The necks now extend parallel to the plate surface rather than perpendicular to it, allowing the effective neck length (which determines resonant frequency) to be increased without increasing the panel thickness. This dimensional change decouples bulk volume from frequency tuning capability.
3Device complexity
If conventional acoustic panels are used for new generation turbomachines with lower frequency noise, then the design is simple, but the acoustic attenuation effectiveness is insufficient
Solution Approach 1:
The patent introduces localized grooves on the inner face of the plate to form the necks. This local modification creates the necessary acoustic neck structure without fundamentally changing the overall panel design. The grooves are precisely positioned and dimensioned to provide the required neck volume and length for frequency tuning, maintaining structural simplicity while achieving enhanced acoustic performance.
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 design enables effective noise attenuation for new generation turbomachines without significant increases in mass or bulk, allowing for efficient noise reduction at lower frequencies without thickness modifications, while also reducing manufacturing costs through symmetrical elements and precise assembly.
Implementation Method 1
each cell in which at least one neck extends, forms a Helmholtz resonator which is able to provide an acoustic attenuation through a visco-thermal dissipation effect at the openings through which the necks open into the cells
Implementation Method 2
acoustic attenuation through a visco-thermal dissipation effect at the openings through which the necks open into the cells
Implementation Method 3
the second plate is impermeable and rigid in order to reflect acoustic waves
Data Source
AI summary
An acoustic panel for an aircraft propulsion unit, comprises a core and an entry layer in contact with the core, the entry layer comprising lower elements and upper elements, each comprising an inner face, an outer face and at least one through-hole, the inner faces of the lower elements and upper elements being in contact with each other and forming a channel defining a baffle and opening into a cell of the core.