Asymmetric airflow and vibration induced by the Coanda effect in a symmetric model of the vocal folds

Abstract

A model constructed from Navier-Stokes equations and a two-mass vocal fold description is proposed in this study. The composite model not only has the capability to describe the aerodynamics in a vibratory glottis but also can be used to study the vocal fold vibration under the driving of the complex airflow in the glottis. Numerical simulations show that this model can predict self-oscillations of the coupled glottal aerodynamics and vocal fold system. The Coanda effect could occur in the vibratory glottis even though the vocal folds have left-right symmetric prephonatory shape and tissue properties. The Coanda effect causes the asymmetric flow in the glottis and the difference in the driving force on the left and right vocal folds. The different pressures applied to the left and right vocal folds induce their displacement asymmetry. By using various lung pressures (0.6-2.0 kPa) to drive the composite model, it was found that the asymmetry of the vocal fold displacement is increased from 1.87% to 11.2%. These simulation results provide numerical evidence for the presence of asymmetric flow in the vibratory glottis; moreover, they indicate that glottal aerodynamics is an important factor in inducing the asymmetric vibration of the vocal folds.

Chaotic component obscured by strong periodicity in voice production system

“…The solution is essentially the same as before. The tests verified that this model is independent of the grid size, time step, and convergence criteria [37,41,42]. The aerodynamic outputs of this model were also compared with previous static model simulations and experimental measurements [27][28][29][30] in a symmetric situation (Q=1).…”

“…An asymmetric composite model, developed from the composite model [37], was employed to predict the vocal fold vibrations induced by complex airflow. The asymmetric two-mass model [13,40] was used to describe the tissue mechanics of vocal folds with unilateral laryngeal paralysis, (1) The displacement vector x α is written as .…”

“…It was found that glottal aerodynamics, such as the pressure distribution, Coanda effect, and others, can be correctly predicted by this model. More details can be found in our previous paper [37].…”

“…These phenomena are also components of glottal airflow [27][28][29][30][31][32][33][34][35]. These complexities of glottal airflow could be responsible for variation in the phonation threshold pressure [36] and for the asymmetric vibration of the vocal fold [37]. However, this causal linkage was not considered in most of the previous studies of irregular vocal fold vibration because the airflow was often simplified in accordance with Bernoulli's law and the laminar, nonviscous, and incompressible assumption.…”

Effect of channel asymmetry on the behavior of flow passing through the glottis

“…Tao et al [12], for example, numerically solved the Navier-Stokes equations to show the occurrence of the Coanda effect in the symmetrical glottis. A similar computational fluid dynamics approach was used for both symmetrical and asymmetrical glottal channels [13,14].…”