Experimental noise source identification in a fuselage test environment based on nearfield acoustical holography

S Ungnad,M Wandel,D Sachau,C Thomas

doi:10.1007/s13272-021-00534-6

S Ungnad, M Wandel + Show 2 more

https://doi.org/10.1007/s13272-021-00534-6

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Abstract

A major challenge in the subject of noise exposure in airplanes is to achieve a desired transmission loss of lightweight structures in the low-frequency range. To make use of appropriate noise reduction methods, identification of dominant acoustic sources is required. It is possible to determine noise sources by measuring the sound field quantity, sound pressure, as well as its gradient and calculating sound intensity by post-processing. Since such a measurement procedure entails a large amount of resources, alternatives need to be established. With nearfield acoustical holography in the 1980s, a method came into play which enabled engineers to inversely determine sources of sound by just measuring sound pressures at easily accessible locations in the hydrodynamic nearfield of sound-emitting structures. This article presents an application of nearfield acoustical holography in the aircraft fuselage model Acoustic Flight-Lab at the Center of Applied Aeronautical Research in Hamburg, Germany. The necessary sound pressure measurement takes one hour approximately and is carried out by a self-moving microphone frame. In result, one gets a complete picture of active sound intensity at cavity boundaries up to a frequency of 300 Hz. Results are compared to measurement data.

Highlights

IntroductionThe measurable acoustic radiation of sound pressure does not allow to draw conclusions about sound sources producing unwanted noise
1.1 Problem statementIn many practical situations, the measurable acoustic radiation of sound pressure does not allow to draw conclusions about sound sources producing unwanted noise
A method based on nearfield acoustical holography (NAH) is being investigated in application to a cylindrical approximation of an aircraft, the Acoustic Flight-Lab (AFL), at the Center of Applied Aeronautical Research in Hamburg, Germany

Summary

Introduction

The measurable acoustic radiation of sound pressure does not allow to draw conclusions about sound sources producing unwanted noise. In the case of an aircraft cabin, this instance can be due to reflections To find those dominant radiating surface segments, called sources, an acoustic intensity measurement would have to be carried out in the entire cabin. A lack of information between vibrations and the resulting radiation of sound pressure is in place when applying conventional measurement methods based on accelerometers, microphones or sound intensity probes. Limited resources often lead to local measurements, whereby information about the sound field is obtained at certain locations and no overall picture of the acoustic environment can be obtained. Measured values that are uncorrelated to the actual sound source due to many reflective surfaces pose additional challenges

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