Producing an accurate model of the human voice has been the goal of researchers for a very long time, but is extremely challenging due to the complexity surrounding the way in which the voice functions. One of the more complicated aspects of modelling the voice is the fluid dynamics of the airflow, by which the process of self-oscillation of the vocal folds is sustained. This airflow also provides the only means by which the ventricular bands (two vocal fold-like structures located a short distance above the vocal folds) are driven into self-oscillation. These have been found to play a significant role in various singing styles and in voice pathologies. This study considers the airflow and flow-structure interaction in an artificial up-scaled model of the human larynx, including self-oscillating vocal folds and fixed ventricular bands. As the majority of any significant fluid-structure interaction takes place between structures found within the larynx, this thesis is limited only to examining this component of the voice organ. Particle Image Velocimetry (PIV) has been used to produce full field measurements of the flow velocity for the jet emerging from the oscillating vocal folds. An important advance in this study is the ability to observe the glottal jet from the point at which it emerges from the vocal folds, thus permitting a more complete view of the overall jet geometry within the laryngeal ventricle than in previous work. Ensemble-averaged PIV results are presented for the experimental model at different phase steps, both with and without ventricular bands, to examine their impact on the dynamics of the human larynx and the glottal jet. Finally, the three-dimensional nature of the glottal jet is considered in order to further understand and test currently held assumptions about this aspect of the jet dynamics. This was achieved by undertaking PIV in a plane perpendicular to that already considered. It is shown that the ventricular bands have an impact on the flow separation point of the glottal jet and on the deflection of the jet centreline. Furthermore, the dynamics of the vocal folds alters when ventricular bands are present, but the glottal jet is found to exhibit similar three-dimensional behaviour whether or not ventricular bands are present.

The vocal folds are essential for speech production, and a better understanding of vocal fold vibration characteristics may help improve treatments of voice disorders. However, studying real vocal folds presents significant challenges. In-vivo studies are limited by access and safety issues. Excised larynges have a short useable lifetime (on the order of minutes) and are difficult to parameterize. In contrast, synthetic vocal fold models have long useable lifetimes and can be easily parameterized. In this thesis, a series of tests performed on recently developed synthetic, self-oscillating models of the human vocal folds are discussed. These tests include measurements of vibration frequency, sub-glottal pressure, and time-averaged flow rate. The differences between one-layer and two-layer synthetic models are evaluated. Comparisons are made between synthetic model and real vocal fold behavior. The synthetic model is shown to have vibrated at frequencies, pressures, and flow rates consistent with human phonation. The influence of sub-glottal tube length on model vibration frequency is examined. Motion is observed using high-speed imaging. Velocity measurements of the glottal jet using particle image velocitmetry (PIV) were performed with and without an idealized vocal tract, including the effects of the false folds, for various cases of vocal tract asymmetry. Glottal jet velocities measured using PIV were consistent with velocities measured using excised larynges. A starting vortex was observed in all test cases. The presence of the false folds acted to restrain the sides of the starting vortex, and in some cases created new vortical structures shed from the false folds. An algorithm was created to calculate and visualize the jet core centerline. In the vocal tract cases, the glottal jet tended to skew toward the nearest wall; in the false fold cases, the opposite trend was observed as the jet skewed away from the nearest wall (towards the midplane). Plots of RMS velocity showed distinct regions of shear layer and jet core. Vocal tract cases at pressures much greater than phonation onset pressure showed significant increases in RMS velocities compared to open jet and false fold cases.

Voice quality is strongly linked to quality of life; those who suffer from voice disorders are adversely affected in their social, family, and professional relationships. An effort has been made to more fully understand the physics behind how the voice is created, specifically the fluid structure interactions that occur during vocal fold vibration. Many techniques have been developed and implemented to study both the motion of the vocal folds and the airflow that creates the motion. Until recently these techniques have sought to understand a highly three-dimensional phenomenon with 1D or 2D perspectives.This research focuses on the development and implementation of an experimental technique to obtain three-dimensional characterizations of vocal fold motion and fluid flow. Experiments were performed on excised human vocal fold models at the University Hospital Erlangen Medical School in Erlangen, Germany. A novel technique for tracking the motion of the vocal folds using multiple camera viewpoints and limited user interaction was developed. Four high-speed cameras (2000 fps) recorded an excised vocal fold model vibrating at 250 Hz. Based on the images from these four cameras a fully 3D reconstruction of the superior surface of the vocal folds was achieved. The 3D reconstruction of 70 consecutive time steps was assembled to characterize the motion of the vocal folds over eight cycles. The 3D reconstruction accurately modeled the observed behavior of vocal fold vibration with a clearly visible mucosal wave. The average reprojection error for this technique was on par with other contemporary techniques (~20 micrometers). A whole field, time resolved, three-dimensional reconstruction of the vocal fold fluid flow was obtained using synthetic aperture particle image velocimetry. Simultaneous 3D flow fields, subglottal pressure waves, and superior surface motion were presented for 2 consecutive cycles of oscillation. The vocal fold fluid flow and motion measurements correlated with behavior observed in previous three-dimensional studies. A higher resolution view of one full cycle of oscillation was compiled from 16 time resolved data sets via pressure data. The result was a full three-dimensional characterization of the evolution and disintegration of the glottal jet.