Anechoic Visco-Thermal Liner for Broadband Noise Attenuation
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Solution Overview
Problem
Conventional acoustic liners face limitations in attenuating a broad range of noise frequencies due to restricted open area and size of openings, leading to reflection of sound energy rather than effective dissipation.
Innovation Solution
The acoustic liner assembly features a large open area with passages much longer than their openings, which are designed to dissipate sound energy through visco-thermal losses, providing a thin profile and minimizing sound reflection across a wide frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the open area of the face sheet is increased to attenuate a broader range of noise frequencies, then the noise attenuation performance is improved, but the manufacturing efficiency decreases due to the increased number and size of openings required
Solution Approach 1:
The patent applies porous materials by using a face sheet with a porous structure that provides a large open area for noise attenuation. The porous structure allows sound waves to enter multiple passages while maintaining manufacturability through established porous material fabrication techniques.
Solution Approach 2:
The patent transitions from two-dimensional surface openings to three-dimensional passages by creating passages that extend through the thickness of the liner. This dimensional change allows the liner to achieve broad frequency attenuation through the depth of the passages rather than requiring numerous surface openings.
2Adaptability or versatility
If the number and size of openings in the face sheet are increased to provide greater open area, then the range of noise frequencies attenuated is improved, but the structural integrity and manufacturing efficiency deteriorate
Solution Approach 1:
The invention moves the noise attenuation function from the two-dimensional face sheet surface to the three-dimensional passages within the liner thickness. This allows the face sheet to maintain its structural integrity while the internal passages provide the necessary open area for broad frequency attenuation.
Solution Approach 2:
The use of porous materials with controlled pore structures allows the creation of passages that provide sufficient open area for noise attenuation while maintaining the overall structural integrity of the liner through the material's inherent strength properties.
3Device complexity
If conventional reactive liners are used to reflect sound energy, then the manufacturing complexity is reduced, but the noise attenuation effectiveness deteriorates due to sound reflection
Solution Approach 1:
The patent converts the harmful reflection of sound energy into beneficial dissipation by designing passages that guide sound waves through the liner thickness where viscous and thermal losses convert the sound energy into heat, rather than reflecting it back into the nacelle.
Solution Approach 2:
The patent replaces the reactive mechanical reflection mechanism with a dissipative mechanism based on visco-thermal losses. Instead of relying on impedance mismatches to reflect sound, the system uses the physical properties of the passage walls to dissipate sound energy through viscosity and thermal conduction.
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 configuration results in improved noise attenuation across a broader frequency range, achieving a substantially anechoic performance with minimal sound reflection and increased manufacturing efficiency.
Implementation Method 1
Sound waves incident on a face of the liner enter the passages and are dissipated by viscous losses
Implementation Method 2
Sound energy is further dissipated as thermal energy to the walls of the passages
Implementation Method 3
The sound wave then travels toward the distal end of the liner where it reflects from a substantially rigid back wall and the propagates back toward the liner face
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A liner assembly (22) includes a plurality of aligned passages (28) providing a large open area combined with openings (30) much smaller than a length (36) of the passages (28). The plurality of passages (28) are disposed parallel with each other and include an opening (30) transverse to incident sound waves. The passages (28) are separated by walls (32) and are blocked at an end distal from the openings (30). Sound waves incident on a face of the liner (22) enter the passages (28) and are dissipated by viscous losses. Sound energy is further dissipated as thermal energy to the walls (32) of the passages (28). The long narrow passages (28) provide the desired visco-thermal losses for sound energy in a broad frequency range.