Nacelle Core Insert for Acoustic Resonance Shift
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Solution Overview
Problem
The increasing size of fan blades in aircraft propulsion systems leads to higher tonal noise levels, and conventional acoustic sandwich panels become excessively thick to effectively attenuate lower frequency noise, limiting their feasibility in nacelle packaging.
Innovation Solution
Incorporating non-permeable inserts within the cells of an acoustic structure to constrict fluid flow, shifting the resonant frequency without increasing the depth of the cells, allowing for tailored sound attenuation without excessive thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the thickness of acoustic sandwich panels is increased to attenuate lower frequency noise, then sound attenuation performance is improved, but the feasibility to package within nacelle loft lines deteriorates
Solution Approach 1:
The patent modifies the resonant frequency parameters of the acoustic panel by adding mass inserts to the core cells. This changes the acoustic behavior of the panel, enabling it to attenuate lower frequency noise generated by larger fans without increasing the overall panel thickness. The mass inserts alter the Helmholtz resonance characteristics of the perforated skin and core structure.
Solution Approach 2:
The patent creates a composite acoustic panel structure by combining the existing sandwich panel construction (skins and core) with additional mass inserts. These inserts are integrated into the core cells to form a composite structure that achieves enhanced low-frequency attenuation while maintaining the original panel thickness and packaging feasibility.
2Productivity
If the size of fan blades is increased, then propulsion efficiency is improved, but tonal noise levels increase
Solution Approach 1:
The patent changes the resonant frequency parameters of the acoustic panel to match and counteract the lower frequency tonal noise generated by larger fan blades. By adjusting the mass and geometry of inserts in the core cells, the panel's attenuation characteristics are optimized for the specific frequency range produced by the enlarged fan.
Solution Approach 2:
The patent converts the harmful low-frequency tonal noise generated by larger fans into a design parameter for the acoustic panel. The noise frequency characteristics are used to determine the optimal resonant frequency of the panel with mass inserts, thereby transforming the noise problem into a solution that targets and attenuates the specific problematic frequencies.
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 approach enables effective attenuation of acoustic power at lower frequencies, such as 0-10 KHz, by modifying the tonal acoustic profile, allowing for flexible design within the constraints of nacelle packaging requirements.
Implementation Method 1
a resonant frequency associated with the structure is shifted by at least a third threshold amount
Implementation Method 2
acoustic power over a frequency range is attenuated by the structure by at least a second threshold amount
Data Source
AI summary
Aspects of the disclosure are directed to a structure comprising: a plurality of cells, a first non-permeable insert in a first cell of the plurality of cells, the first insert configured to constrict, by at least a first threshold amount, a flow of fluid in the first cell such that: acoustic power over a frequency range is attenuated by the structure by at least a second threshold amount, and a resonant frequency associated with the structure is shifted by at least a third threshold amount.