Acoustic Liner Design Using Convoluted Paths for Low-Frequency Noise
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Solution Overview
Problem
Conventional acoustic liners in aerospace applications are ineffective at absorbing sound with dominant frequency content below 1000 Hz due to volume and weight constraints, failing to address low-frequency noise which can cause structural vibration, passenger discomfort, and environmental pollution.
Innovation Solution
A method for designing acoustic liners using a Low-Frequency Performance Metric (LFP) and the Zwikker-Kosten Transmission Line Code (ZKTL) to optimize the configuration of core cells and acoustic paths, extending the acoustic path length and creating convoluted paths to enhance sound absorption at low frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional acoustic liners are used, then weight and volume constraints are satisfied, but low-frequency sound absorption below 1000 Hz is ineffective
Solution Approach 1:
The patent extends the acoustic path length by creating convoluted three-dimensional paths within the liner structure. Instead of simple straight-through paths, the design incorporates multiple reflections and extended trajectories that increase the effective path length from the incident face to the exit face, thereby enhancing low-frequency absorption without increasing the external dimensions of the liner.
Solution Approach 2:
The patent employs curved and convoluted acoustic paths rather than straight linear paths. The sound wave trajectories are designed to follow curved routes through the liner material, increasing the interaction length between the sound waves and the absorptive material, which improves low-frequency absorption performance within constrained volume.
2Object-affected harmful factors
If conventional acoustic liners are used, then weight constraints are satisfied, but low-frequency sound absorption below 1000 Hz is ineffective
Solution Approach 1:
The patent achieves enhanced low-frequency absorption by extending the acoustic path length through three-dimensional convoluted paths within the existing weight budget. The increased path length allows for better absorption of low-frequency sounds without requiring additional material mass, thereby maintaining weight constraints while improving acoustic performance.
Solution Approach 2:
By designing curved convoluted paths for sound wave propagation, the patent increases the effective interaction length between sound waves and absorptive material without proportionally increasing weight. The curved trajectories allow more absorption events to occur within the same material mass, improving low-frequency absorption efficiency.
3Object-affected harmful factors
If acoustic path length is extended to improve low-frequency absorption, then absorption coefficient increases, but liner volume increases
Solution Approach 1:
The patent resolves this contradiction by extending the acoustic path in the third dimension through convoluted three-dimensional paths. The sound waves traverse longer distances within the same external volume by following complex trajectories that reflect multiple times off internal surfaces, thereby increasing the absorption coefficient without proportionally increasing the liner's external dimensions.
Solution Approach 2:
The curved convoluted paths allow the sound waves to travel longer distances through the absorptive material within the same physical volume. The curvature and complexity of the paths increase the interaction length between sound and material, achieving higher absorption coefficients without requiring larger external dimensions.
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 method achieves exceptional broadband absorption at frequencies below 500 Hz, providing a 38.1 mm deep liner with over 100 Hz continuous bandwidth and absorption coefficient greater than 0.6, effectively reducing low-frequency noise in aircraft engines.
Implementation Method 1
The method achieves exceptional broadband absorption at frequencies below 500 Hz
Implementation Method 2
sound absorption at low frequencies
Implementation Method 3
acoustic energy to thermal energy conversion
Implementation Method 4
extending the acoustic path length and creating convoluted paths to enhance sound absorption
Data Source
AI summary
A method of designing an acoustic liner includes identifying acoustic path lengths that will attenuate a frequency within a frequency range of interest, and selecting a liner configuration with a combination of acoustic paths that addresses the frequency range of interest. The selection may be made after a comparison of the response of different liner configurations.