Noise Reduction Potential of Cellular Metals

Björn Hinze,Joachim Rösler,Nicolas Lippitz

doi:10.3390/met2020195

Abstract

Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 °C only metallic or ceramic structures can be used. Due to fatigue loading and the notch effect of the pores, mechanical properties of porous metals are superior to the ones of ceramic structures. Consequently, cellular metals like metallic foams, sintered metals, or sintered metal felts are most promising materials. However, acoustic absorption depends highly on pore morphology and porosity. Therefore, both parameters must be characterized precisely to analyze the correlation between morphology and noise reduction performance. The objective of this study is to analyze the relationship between pore morphology and acoustic absorption performance. The absorber materials are characterized using image processing based on two dimensional microscopy images. The sound absorption properties are measured using an impedance tube. Finally, the correlation of acoustic behavior, pore morphology, and porosity is outlined.

Highlights

Due to increasing traffic, many people are exposed to significant noise loads causing insomnia and other reactions, which impair health and productivity [1,2]
This study focuses on cellular metals, which can resist elevated temperatures as well as fatigue loading and, resemble geometrically conventional passive absorbers
Materials with higher porosity show higher absorption due to reduced reflection of sound waves from the surface of the absorber material, since acoustic absorption can only be reached if the acoustic waves can couple into the absorber

Summary

Introduction

Many people are exposed to significant noise loads causing insomnia and other reactions, which impair health and productivity [1,2]. The rising number of flights and aircrafts causes an excessive air traffic noise increase. To change this development, various approaches have. Due to the elevated temperatures and high fatigue loading in this part of the aero-engine, conventional passive absorber materials cannot be used. This study focuses on cellular metals, which can resist elevated temperatures as well as fatigue loading and, resemble geometrically conventional passive absorbers. Depending on the production processes, e.g., sintering of metal fibers [3], powder processing using a foaming agent [4], coating of polymer foams [5], or melt infiltration techniques [6], the characteristic dimensions of the porosity are usually in a range of 0.01 mm to 10 mm

Objectives

Findings

Discussion

Conclusion