Annular Canal Acoustic Absorption Structure for Broadband Noise Attenuation
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Solution Overview
Problem
Existing acoustic absorption structures for noise attenuation in aircraft propulsion systems either limit frequency bands or increase mass and thickness when attempting to broaden frequency coverage.
Innovation Solution
An acoustic absorption structure comprising a porous layer, a cellular layer with cells featuring exterior and interior annular canals, and a reflective layer, where the cells have concentric annular canals and partitions with corrugations, allowing for efficient noise attenuation across a broad frequency range while maintaining a thinner design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single cellular layer with conventional honeycomb structure is used, then the structure maintains low mass and thickness, but noise attenuation is limited to narrow frequency bands
Solution Approach 1:
The patent implements nested annular canals within each cell structure, where inner canals are positioned within outer canals. This nesting arrangement allows multiple acoustic pathways of different dimensions to coexist in a single cellular layer, enabling broad frequency attenuation without requiring multiple stacked layers, thus maintaining low mass and thickness while expanding frequency coverage
Solution Approach 2:
The patent transitions from conventional planar honeycomb structures to three-dimensional annular canal systems with radial and axial dimensions. The annular canals extend through the thickness of the cellular layer, creating volumetric acoustic pathways that interact with sound waves across multiple frequency ranges simultaneously, thereby broadening the effective frequency band without increasing overall structure thickness
2Adaptability or versatility
If two cellular layers are stacked to broaden frequency coverage, then the frequency band increases, but mass and thickness of the structure increase
Solution Approach 1:
The patent merges multiple acoustic functions into a single cellular layer by incorporating both outer and inner annular canals within the same structural unit. This consolidation achieves the frequency broadening effect of multiple stacked layers while eliminating the additional mass and thickness that would result from stacking, as all acoustic pathways are integrated within one layer thickness
Solution Approach 2:
By nesting inner annular canals within outer annular canals in the same cellular layer, the patent creates a compact multi-functional structure that provides diverse acoustic attenuation pathways without requiring additional structural layers, thereby avoiding the mass and thickness penalties of stacked configurations
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 structure effectively attenuates noise over a broad band of frequencies with reduced thickness, mimicking the performance of dual honeycomb structures while minimizing mass and thickness.
Implementation Method 1
The porous layer 12 has a dissipative role, partially converting the acoustic energy of the sound wave passing through it into heat.
Implementation Method 2
each cell comprises at least one exterior annular canal, delimited by two concentric first lateral walls
Implementation Method 3
Such an acoustic absorption structure allows noise to be attenuated for a given frequency or a narrow band of frequencies
Data Source
AI summary
An acoustic absorption structure includes: a porous layer in contact with a medium through which the sound waves travel, a cellular layer including a plurality of cells, which has at least one exterior annular canal open towards the porous layer, and a reflective layer. An aircraft propulsion system having at least one such acoustic absorption structure is also described.