Effect of expiratory flow rate on the acoustic characteristics of sibilant /s/

Abstract

Sibilant /s/, which is an unvoiced sound, is believed to be produced by a jet of air through a sibilant groove toward the sharp edges of the teeth. We investigated what effects the expiratory flow rate had on the acoustic characteristics of sibilant /s/ in the present study. A large eddy simulation was implemented to investigate the flow in an oral cavity model that simplified the important anatomical features of the oral cavity when sibilant /s/ was pronounced. The results illustrated that an increase in the expiratory flow rate caused turbulence to develop in the separated flow from the edge of the obstacle wall which mimics a tooth. The increase in turbulent intensity induced a dramatic elevation in Lamb-vector divergence in the flow-separation region, which was regarded as a sound source of sibilant /s/. The total power of the sound source which was located near the obstacle edge of the obstacle wall at smaller flow rates, extended downstream in the flow separation as the expiratory flow rate increased through which turbulence developed. These results demonstrated that the expiratory flow rate had a significant influence on the acoustic characteristics of sibilant /s/ particularly when the flow rate increased to cause turbulence.