| Summary: | 博士 === 國立臺灣大學 === 機械工程研究所 === 82 === Ever since the invention of reciprocating internal (I.C.)
engine, exhaust noise has been a major source of urban noise
pollution. In recent years, consumer awareness as well as
government regulations are encouraging the use of
sophisticated design procedures to develop low engine exhaust
noise as well as efficiency of engine performance. In order to
guarantee good attenuation at the firing frequency (or any of
its multiples),where the unattenuated pulsating noise
resulting from I.C. engine is maximum, various
geometrical configurations of the perforated elements (e.g.,
concentric-tube resonators, and cross-flow elements) have been
developed. These configurations may be one of the straight-
through types or the reversed-flow types. Straight-through type
mufflers are normally preferred because they result in
broadband frequency attenuation without significant increase
in resistance to the flow of gas, whereas reversed-flow type
mufflers are used when an exhaust system is being designed
to achieve large amplitude, narrowband frequency attenuation as
in the case of an I.C. engine that runs at constant speed.
Generally, straight-through type mufflers offer low
resistance to the flow of gases and, consequently, maintain
lower engine back-pressures. These are, however,
acoustically not very effective. Mufflers with flow
reversals, on the other hand, offer increased attenuation but
at the cost of higher engine back-pressures. Finally, some
comments are offered on the design thumb of perforated
element mufflers. By tuning the length and associate physical
parameter to the in-situ case of various tubular
elements, one can achieve rapid and economical modeling
these that are frequently used in commercial reactive mufflers
as well as in many other industrial applications. The
aeroacoustic modeling ability is very useful for vehicular
muffler designer especially in the preliminary design stage.
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