Aircraft APU Silencer with Segmented Acoustic Cells
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing silencers for aircraft auxiliary power units face challenges in effectively dampening exhaust gas noise across a broad frequency range without increasing their external dimensions, leading to insufficient sound absorption, particularly due to inadequate cell design and resonance issues.
Innovation Solution
The silencer design features non-equidistantly arranged partitions that create varying cell lengths and volumes, incorporating a porous absorber layer to enhance sound absorption, and an annular channel at the outlet to cancel out resonant vibrations, allowing for efficient noise reduction in a compact form.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the diameter of the flow channel is increased to improve sound dampening, then the first transversal mode can be dampened sufficiently, but the second transversal mode remains insufficiently dampened and the device dimensions increase
Solution Approach 1:
The silencer is segmented into multiple cells of varying lengths arranged in series along the flow channel. This segmentation allows different cell lengths to target different transversal modes independently, achieving broadband noise reduction without increasing the overall diameter of the silencer.
Solution Approach 2:
Different cell lengths are assigned to different positions along the flow channel to create local variations in acoustic impedance. This local quality variation enables effective dampening of multiple transversal modes at different locations, improving sound dampening efficiency without enlarging the device.
2Object-affected harmful factors
If the silencer length is increased to dampen more transversal modes, then sound dampening efficiency improves, but the external dimensions and installation space requirements increase
Solution Approach 1:
The flow channel is divided into multiple discrete cells with different lengths rather than using a single long channel. This segmentation allows the silencer to achieve broadband noise reduction through a compact arrangement of varied cell lengths, reducing the overall length compared to a conventional single-channel design.
Solution Approach 2:
Instead of extending the silencer length linearly to dampen multiple modes, the invention uses dimensional variation in cell lengths within a compact series arrangement. This approach achieves multi-mode dampening in a more space-efficient configuration.
3Ease of manufacture
If equidistant partitions are used to simplify manufacturing, then device complexity is reduced, but sound dampening efficiency across broadband frequencies is insufficient
Solution Approach 1:
The partitions are arranged asymmetrically with non-equidistant spacing, creating cells of varying lengths. This asymmetric arrangement is specifically designed to target different transversal modes at different frequencies, achieving effective broadband noise reduction while maintaining manufacturing feasibility.
Solution Approach 2:
Different partition spacing is applied at different locations along the flow channel to create local variations in cell length. This local quality variation optimizes sound dampening for multiple frequency ranges, improving noise emission reduction compared to uniform spacing.
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 design achieves superior sound dampening efficiency per length unit, effectively reducing broadband noise and high-frequency components, while maintaining a compact size, thereby improving noise reduction without enlarging the silencer's external dimensions.
Implementation Method 1
allows an alternating flow transverse thereto through the wall material of the flow channel and into the individual cells such that friction converts sound energy into heat during the passage through the wall material of the flow channel
Implementation Method 2
the sound dampening is very low for certain frequency ranges due to standing waves in the silencer
Implementation Method 3
incorporating a porous absorber layer to enhance sound absorption
Data Source
AI summary
A silencer for an auxiliary power unit of an aircraft comprises an inlet, an outlet, a housing and a flow channel with a porous wall material that is arranged in the housing. An intermediate space is formed between the housing and the flow channel and divided into outer cells that are arranged around the flow channel by means of one or more partitions. This makes it possible to realize a very compact silencer with very good sound insulation properties. The sound dampening can be additionally improved by dividing the outer cells into outer regions and inner regions, by adapting the shape of the silencer to a tail section of an aircraft and by arranging an annular channel on the outlet.