Fluid flow in a dynamic mechanical model of the vocal folds and tract. I. Measurements and theory

In this study, aerodynamic and acoustic measurements were obtained in a dyn amic mechanical model of the larynx and vocal tract. The model consisted of a uniform duct, intersected by a pair of sinusoidally oscillating shutters . A controlled ah-flow along the duct was periodically disturbed by the act ion of the shutters and pressure, and flow velocity measurements were obtai ned in the region downstream. The velocity held in the duct could be decomp osed into three distinct components: a mean how, a fluctuating acoustic par ticle velocity, and a fluctuating nonacoustic velocity associated with the transport of vortices along the duct at the local mean flow velocity. Two t heoretical models for sound radiation from the duct exit were investigated. The first was based on the in-duct acoustic field alone and was unable to provide a realistic prediction of the measured, radiated sound field except at the first formant of the duct. In the second a simple description of so und generation due to the interaction of vortices with the duct exit was ad ded. In this case much closer prediction of the measured values was achieve d, leading to the conclusion that the interaction of the nonacoustic veloci ty fluctuation with the duct boundaries results in a significant additional source of acoustic energy located in the region of the duct exit. (C) 1999 Acoustical Society of America. [S0001-4966(99)00401-4].