05-10-2012, 05:17 PM
Acoustic attenuation performance analysis of multi-chamber reactive silencers
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Introduction
The multi-chamber reactive silencers are widely used to reduce engine exhaust noise as well as
blower intake and discharge noise. Davis et al. [1] developed a one-dimensional analytical
approach, which assumes plane wave propagation in the axial direction in silencers, to predict the
acoustic attenuation performance of double expansion chamber reactive silencers, and compared
the predictions with experimental results. They investigated the effect of the length of interconnecting
tube on the acoustic attenuation performance of the silences with chambers of equal
lengths. The transfer matrix approach based on the one-dimensional plane wave theory is
described in detail by Munjal [2] for several acoustic elements and silencer configurations. The
plane wave theory, however, excludes the effect of multi-dimensional waves inside the silencers.
Thus, while yielding reasonable predictions at lower frequencies, the simplistic approach is
expected to deviate from experimental results at higher frequencies. Above the plane wave cut-off
frequency, one-dimensional plane wave approach is not applicable to predict the acoustic
attenuation performance of silencers. For the large size silencers, the plane wave cut-off frequency
is lower and high-frequency acoustic attenuation performance prediction is still desired for the
purpose of noise control.
Results and discussion
For all configurations, the present study considers d=600 and D=1800 for the inlet/outlet tube
and silencer diameters, respectively, and speed of sound c=344 m/s.
Fig. 2 shows the transmission loss comparison of single, double and triple expansion chamber
silencers with equal length (2400) for each chamber. The double chamber silencer provides much
higher acoustic attenuation than the single chamber silencer and the triple chamber silencer
exhibits a higher acoustic attenuation than the double chamber silencer at most frequencies in the
plane wave region. At higher frequencies, the acoustic attenuation of the multiple chamber
silencers is slight higher than the single chamber silencer, but the acoustic behavior is complex.
Conclusions
A numerical approach based on the three-dimensional substructure boundary element
technique is developed to predict and analyze the acoustic attenuation performance of multichamber
reactive silencers with inter-connecting tube(s). The effect of geometry on acoustic
attenuation performance of the silencers is investigated in detail. In general, the multiple chamber
silencers provide higher acoustic attenuation than the single chamber silencer at most frequencies
after their pass frequencies. Below their pass frequencies, the use of multiple chambers lowers the
acoustic attenuation compared to the single chamber silencer with the same silencer length.
Reasonably, choosing the lengths of extended inlet/outlet tubes and inter-connecting tube may
obtain a desired broadband high noise attenuation characteristics. The dual inter-connecting
tubes improve the acoustic attenuation performance of the silencer at higher frequencies.