Studies on Noise Generated by Flow in Expansion Chamber Type Silencers : 1st Report, The Effects of the Geometric Parameters on Noise Characteristics

Abstract

This report describes the effects of the geometric parameters on the characteristics of secondary noise generated by the airflow in silencers constructed with a single expansion chamber. The peak values occur, regardless of the tailpipe resonance, on a noise spectrum measured for each chamber whose length lc is smaller than four times of the duct diameter d. The frequency fp at which a peak is highest may be predicted by Strouhal numbers (fp·lc/V, V : mean flow velocity) arranged as a function of lc/d. The overall noise levels computed by using individual spectra obtained for many chambers are dependent on the geometric factors when lc/d lies between 2.5 and 6, but reduce with the decreasing area expansion ratio and the increasing camber length in the range 6<lc/d<20.