Micro-perforated Acoustic Liner for Aircraft Engine Noise
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Solution Overview
Problem
Conventional noise attenuation liners for aircraft engines face challenges in achieving optimal noise reduction across a wide range of frequencies while minimizing drag and maintaining durability, often requiring increased maintenance due to the use of woven mesh liners.
Innovation Solution
A noise attenuation liner assembly featuring a cellular structure covered by a perforated face sheet with openings of specific diameters and configurations, designed to minimize drag and maximize acoustic attenuation, using a non-linearity factor and resistance values to optimize airflow and acoustic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a woven mesh liner is used to cover the cellular structure, then noise attenuation over a broad range of frequencies is improved and skin friction coefficient is reduced, but durability deteriorates and maintenance requirements increase
Solution Approach 1:
The patent changes the geometric parameters of the face sheet by introducing a specific perforation pattern with holes having diameter D and center-to-center spacing S, where S is between 2D and 10D. This parameter optimization allows the liner to achieve broad frequency noise attenuation while maintaining durability, eliminating the need for woven mesh overlays.
Solution Approach 2:
The patent creates a composite structure by integrating the perforated face sheet directly with the cellular core, forming a single durable assembly. This composite design eliminates the separate woven mesh layer that previously caused durability issues, while maintaining both noise attenuation performance and structural integrity through the optimized perforation pattern.
2Object-generated harmful factors
If the openings in the face sheet are made larger, then airflow drag is reduced, but acoustic attenuation performance deteriorates
Solution Approach 1:
The patent optimizes the parameters by specifying that hole diameter D should be between 0.002 inches and 0.010 inches, and center-to-center spacing S should be between 2D and 10D. This parameter range achieves the optimal balance where drag is sufficiently reduced for engine performance while acoustic attenuation remains effective across the target frequency range.
Solution Approach 2:
The patent applies local quality by creating zones of different perforation densities across the face sheet. The optimized spacing ratio (S between 2D and 10D) creates local flow patterns that minimize drag while maintaining acoustic performance, allowing different regions to optimize for either airflow or noise attenuation as needed.
3Measurement precision
If the liner is tuned to attenuate specific undesirable frequencies, then attenuation efficiency at those frequencies is improved, but effective attenuation of other noise frequencies is limited
Solution Approach 1:
The patent achieves universality by designing a perforated face sheet that simultaneously provides effective noise attenuation across multiple frequency ranges. The optimized perforation pattern (D between 0.002-0.010 inches, S between 2D-10D) enables the single structure to function effectively for both low-frequency and high-frequency noise, eliminating the need for frequency-specific tuning compromises.
Solution Approach 2:
The patent changes the face sheet parameters to create a broadband attenuation solution. By specifying D between 0.002 inches and 0.010 inches and S between 2D and 10D, the design achieves multi-functionality where the same structural parameters provide effective attenuation across diverse frequency ranges, unlike conventional tuned liners that optimize for narrow bands.
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 solution provides improved acoustic performance, reduced drag, and increased durability across a wide range of engine operating conditions, ensuring effective noise attenuation with minimal maintenance costs.
Implementation Method 1
a cellular structure for dissipating acoustic energy
Implementation Method 2
The perforated face sheet includes a plurality of openings to communicate acoustic energy to the underlying cellular structure
Data Source
Figure 1~2
Figure 3~4
AI summary
An example liner assembly (22) includes a backing plate that supports a cellular structure (26) covered by a perforated face sheet (28) including a plurality of openings (32). The surface of the face sheet (28) includes a surface finish no greater than an equivalent sand-grain roughness of 0.0003 inches.