Fluid dynamic effects in speech
Michael Krane · The Journal of the Acoustical Society of America · 1999
A summary of fluid dynamic effects in speech are outlined using concepts from duct flow aerodynamics and aeroacoustics. A physical picture of fluid motion which produces both voiced and unvoiced sounds is presented, with emphasis on how movement of the acoustic medium affects both the generation and propagation of sound. Particular attention is given to the concept of vorticity (roughly, fluid particle rotational motion) as a means to characterize turbulent flow and as the means by which airflow produces or absorbs sound. First, it is shown how vorticity production by steady flow at the end of an open pipe may act as an absorber of sound, affecting the acoustic impedance of the open end. Unvoiced sound production is then discussed in terms of the formation of a jet by flow separation, the structure of jet vorticity, and how convection of jet vorticity through a nonuniform vocal tract produces sound. Order-of-magnitude estimates of these effects are presented. Finally, the role of these effects in voice production are detailed through a discussion of the modulation of glottal volume flow by movement of the glottal flow separation point and production of sound by the glottal jet.