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Research Papers

# A New Type of Muffler Based on Microperforated Tubes

[+] Author and Article Information
S. Allam

Department of Automotive Technology, Faculty of Industrial Education, Helwan University, Elsawah Street, Elkoba 11282, Cairo, Egyptallam@kth.se

M. Åbom

The Marcus Wallenberg Laboratory for Sound and Vibration Research, AVE, KTH, SE-10044 Stockholm, Sweden

J. Vib. Acoust 133(3), 031005 (Mar 25, 2011) (8 pages) doi:10.1115/1.4002956 History: Received January 18, 2010; Revised July 31, 2010; Published March 25, 2011; Online March 25, 2011

## Abstract

Microperforated plate (MPP) absorbers are perforated plates with holes typically in the submillimeter range and perforation ratios around 1%. The values are typical for applications in air at standard temperature and pressure (STP). The underlying acoustic principle is simple: It is to create a surface with a built in damping, which effectively absorbs sound waves. To achieve this, the specific acoustic impedance of a MPP absorber is normally tuned to be of the order of the characteristic wave impedance in the medium ($∼400 Pa s/m$ in air at STP). The traditional application for MPP absorbers has been building acoustics often combined with a so called panel absorber to create an absorption peak at a selected frequency. However, MPP absorbers made of metal could also be used for noise control close to or at the source for noise control in ducts. In this paper, the possibility to build dissipative silencers, e.g., for use in automotive exhaust or ventilation systems, is investigated.

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## Figures

Figure 1

Photo of one commercial MPP absorber based on slit-shaped holes (Acustimet™). The slit length l shown in the figure is around 5 mm.

Figure 2

Schematic of a MPP and definition of thickness (t) and diameter/width (d)

Figure 3

Flow distribution and the acoustic waves in the test object

Figure 4

Measurement configuration for two-port measurements at MWL

Figure 5

Educed normalized impedance versus frequency at different flow Mach numbers for sample C3. Resistive values are nearly horizontal and the reactive values are inclined.

Figure 6

Comparison between measured and predicted impedances (real parts that are almost constant and imaginary parts that are increased with frequency) versus frequency at different flow Mach numbers for sample C1

Figure 7

MPP muffler geometry

Figure 8

Results with different impedances z for the dividing wall in the middle of the muffler in Fig. 7

Figure 9

MPP muffler with four chambers separated by rigid walls

Figure 10

Results with two chambers (—) and four chambers (---) using hard walls

Figure 11

MPP muffler with three chambers separated by rigid walls

Figure 12

Simulated and measured TL for a MPP (sample C1) muffler (no flow) with geometry as shown in Fig. 1. L=500 mm and r1=28.5 mm and r2=75 mm.

Figure 13

Simulated and measured TL for a MPP (sample C1) muffler at different flow Mach numbers. L1=L2=L3=161.3 mm and r1=28.5 mm and r2=75 mm.

Figure 14

Simulated and measured TL for a MPP (sample C1) muffler at different flow Mach numbers. L1=164 mm, L2=210 mm, and L3=110 mm and r1=28.5 mm and r2=75 mm.

Figure 15

Effect of SPL (incident wave) on simulated TL for a MPP (sample C1) muffler. L1=164 mm, L2=210 mm, and L3=110 mm and r1=28.5 mm and r2=75 mm at M=0.0.

Figure 16

Effect of SPL on simulated TL for a MPP (sample C1) muffler. L1=164 mm, L2=210 mm, and L3=110 mm and r1=28.5 mm and r2=75 mm at M=0.1.

Figure 17

Simulated TL for a MPP (sample C1) muffler at 500°C and normal pressure. L1=164 mm, L2=210 mm, and L3=110 mm and with r1=28.5 mm and r2=75 mm at different flow Mach numbers.

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