Aircraft APU Silencer with Permeable Central Body
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Solution Overview
Problem
Conventional silencers for aircraft auxiliary power units are limited in sound attenuation without increasing their outer dimensions, which restricts noise reduction effectiveness.
Innovation Solution
A silencer design featuring a central body with a permeable casing that divides the flow channel into inner cells, aligned coaxially with the inlet, and a perforated walling to optimize sound attenuation by decoupling resonance frequencies and enhancing flow resistance, allowing for improved noise reduction without enlarging the silencer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the outer dimensions of the silencer are enlarged to increase sound attenuation, then sound attenuation is improved, but the silencer size increases
Solution Approach 1:
The silencer is divided into multiple cells (first cell, second cell, third cell) separated by partitions. Each cell contains acoustic absorption material and is equipped with acoustic outlets. This segmentation allows the silencer to achieve enhanced sound attenuation through multiple absorption zones without proportionally increasing the overall silencer volume, as the cells are arranged to utilize the available space efficiently.
Solution Approach 2:
The invention introduces a vertical dimension to the acoustic absorption structure by arranging cells at different heights and using partitions that extend vertically. The acoustic outlets are positioned at different levels, creating a three-dimensional absorption pattern that increases sound attenuation effectiveness without requiring a proportional increase in the horizontal footprint of the silencer.
2Object-affected harmful factors
If the number of cells is increased to improve sound attenuation, then sound attenuation is improved, but device complexity increases
Solution Approach 1:
Each cell in the silencer serves multiple functions: it contains acoustic absorption material for sound attenuation, has acoustic outlets for controlled exhaust gas discharge, and is separated by partitions that also serve as structural supports. This multi-functionality reduces the need for additional components, thereby limiting the increase in device complexity even as the number of cells is increased for improved sound attenuation.
Solution Approach 2:
The partitions between cells are designed with specific local properties, such as openings or different material compositions, to optimize acoustic flow and gas discharge in each cell. This localized optimization allows for improved sound attenuation in specific frequency ranges without requiring uniform complex structures throughout the entire silencer, thus managing overall device complexity.
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 design achieves significant sound attenuation across a wide frequency range, reducing noise pollution from auxiliary power units without increasing the silencer's size, by converting acoustic energy to heat and decoupling resonance frequencies, resulting in better noise reduction compared to conventional silencers.
Implementation Method 1
acoustic energy is converted to heat as a result of friction
Implementation Method 2
the resonant frequency of the inner cells corresponds to the natural frequency of the first radial mode in a channel formed between the casing of the central body and the inner surface of the inlet
Data Source
AI summary
A silencer for an auxiliary power unit of an aircraft includes an inlet, an outlet, a housing, and a flow channel of a porous material, arranged in the housing. Between the housing and the flow channel an intermediate space is created, which space is divided by at least one outer partition into outer cells arranged around the flow channel. A central body includes a casing that is permeable to gas at least in some regions and that is arranged in the interior of the silencer. The central body includes inner partitions dividing the central body into inner cells. The resonance frequency of the inner cells corresponds to the natural frequency of the first radial mode in a channel formed between the central body and the inner surface of the inlet. In this manner particularly good sound attenuation is achieved with a compact installation space of a silencer.