Instantaneous orifice discharge coefficients of driven physical models of the human larynx

Jong Beom Park, Purdue University

Abstract

This thesis describes an investigation of voiced sound production and air flow through the human larynx during phonation. The research objectives were to: (1) establish the contribution of intrinsically unsteady effects, such as local flow acceleration and flow induced by wall motion; and (2) determine the influence of a posterior commissure. Driven physical rubber models of the human larynx were created and used. The physical models geometry was based on idealized glottal geometries with converging and diverging orifice profiles. Measurements were made to characterize the flow velocity over the orifice discharge, the static and acoustic pressures across the orifice, and the orifice area. The instantaneous orifice discharge coefficient was then calculated based on measured data using Bernoulli's obstruction theory. Different tube configurations were used in order to simulate the presence of the vocal tract and the subglottal part of the humans airway. The instantaneous orifice discharge coefficient (ODC) of the shoving wall orifice was shown to be indicative of the dipole acoustic source strength. Instantaneous ODC values were compared with ODC values measured for static orifice configurations with geometries and boundary conditions snatching those of the dynamic moving wall orifice at specific times over the glottal cycle. The results indicated that the quasi-steady approximation often made in voice production modeling was accurate over nearly 70% of the glottal duty cycle. The flow though the shoving wall orifice only deviated from a steady flow through static orifices near the beginning and the end of the glottal cycle. The main causes of the deviations were the effects of the flow entrained by wall motion, Coanda effects and viscous effects. The orifice coefficients of flow through an orifice with an incomplete closure, was also found to vary over one glottal cycle, indicating hysteretic behavior. Numerical simulations were finally performed to quantify the contribution of the displacement flow to the pressure-driven flow field, and the radiated sound. The monopole and dipole source strengths associated with the motion of the orifice walls were calculated.

Degree

Ph.D.

Advisors

Mongeau, Purdue University.

Subject Area

Mechanical engineering

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