Effects of Vertical Glottal Duct Length on Intraglottal Pressures in the Convergent Glottis

Sheng Li,Mingxi Wan,Ronald C Scherer

doi:10.3390/app11104535

Abstract

In a previous study, the vertical glottal duct length was examined for its influence on intraglottal pressures and other aerodynamic parameters in the uniform glottis [J Voice 32, 8–22 (2018)]. This study extends that work for convergent glottal angles, the shape of the glottis during the glottal opening phase of vocal fold vibration. The computational fluid dynamics code ANSYS Fluent 6.3 was used to obtain the pressure distributions and other aerodynamic parameters for laminar, incompressible, two-dimensional flow in a static vocal fold model. Four typical vertical glottal duct lengths (0.108, 0.308, 0.608, 0.908 cm) were selected for three minimal diameters (0.01, 0.04, 0.16 cm), three transglottal pressures (500, 1000, 1500 Pa), and three convergent glottal angles (−5°, −10°, −20°). The results suggest that a longer vertical glottal duct length increases the intraglottal pressures, decreases the glottal entrance loss coefficient, increases the transglottal pressure coefficient, causes a lower gradient of both the intraglottal flow velocity and the wall shear stress along the glottal wall—especially for low flows and small glottal minimal diameters—and has little effect on the exit pressure coefficient and volume flow. The vertical glottal duct length in the convergent glottis has important effects on phonation and should be well specified when building computational and physical models of the vocal folds.

Highlights

Phonation is the result of complex nonlinear coupling between aerodynamic and physiological parameters
The larger the minimal diameter, the larger the effect of transglottal pressure. These results suggest that the glottal minimal diameter and transglottal pressure are the primary controllers of volume flow, and the vertical glottal duct length for convergent glottal shapes has relatively little effect on the volume flow
The results suggest that a change of the vertical glottal duct length appears to have only small effects on the exit coefficient, transglottal pressure coefficient, volume flow, and tangential forces that act upon the vocal folds

Summary

Introduction

Phonation is the result of complex nonlinear coupling between aerodynamic and physiological parameters. The glottal geometry parameters include glottal angle [2], glottal inferior and superior vocal fold surfaces [3], glottal entrance and exit radii [4,5], and the symmetry and obliquity of the glottis [1] These time-variant glottal geometry parameters significantly affect the glottal volume velocity and affect the spectral shape of the output acoustics [6]. The word “vertical” is used due to the fact that, for a standing or sitting individual, the inferior-to-superior duct of the glottis is in a vertical orientation This term is similar to another vocal fold geometry parameter called the “vocal fold thickness” reported by Hollien and Colton in 1969 [8] and defined as the cross-sectional area of the vocal fold (seen in the frontal view) divided by the vocal fold width. The vocal fold thickness typically would be slightly longer than the vertical glottal duct length [7]

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Conclusion