Experimental Study of acoustic characteristics of expansion chamber with mean flow

Abstract

For the measurement of transmission loss of the silencers which have mean flow, the noise levels of signals depicted by microphone usually prohibit accurate measurements of the transmission loss. To overcome this difficulty, static pressure compensation technique has been developed to increase the dynamic range of the microphones, resulting accurate measurement of transmission loss in the presence of high noise level. Series of experiments to investigate the acoustic characteristics of expansion chamber with mean flow has been performed using the pressure compensated microphones. Results demonstrate: (1) frequency shift due to the presence of mean flow, (2) effect of length, diameter, offset length and twisting angles to the transmission loss of expansion chamber with and without mean flow(up to 50m/sec), (3) relation between the proposed parameter aspect ratio and number of peaks of transmission loss in low frequency region.