Fluid -structure interactions within the human larynx
Abstract
The flow-induced vibrations of the vocal folds were investigated using physical and computational models in order to study the fluid-structure interactions within the human larynx. Aspects of laryngeal self-oscillations that were investigated include the role of surface adhesive forces, the influence of orifice profile, and energy transfer mechanisms. The physical model was fabricated using a polyurethane compound. The model size, shape, and material properties were generally similar to corresponding human vocal folds characteristics. Regular, large-amplitude, self-sustained oscillations were achieved at a frequency of approximately 120 Hz. The onset pressure was approximately 1.2 kPa. It was found that relatively weak surface adhesive forces caused the appearance of a maximum in the frequency-subglottal pressure relation, a change in the slope of the area time history during the opening phase, and a highly localized surface deformation and acceleration. It is possible that such forces may contribute to vocal fold damage in cases of dehydration of the laryngeal mucus lining. Simulations of the flow through a collapsible channel were performed using finite element analysis. The influence of a wall constriction on the steady and unsteady wall deformation and the resulting flow patterns was investigated. The system response was found to be very sensitive to changes in orifice profile, and less sensitive to changes in orifice height. Energy transfer analysis of the unconstricted channel showed that the contribution of viscous fluid stresses to the overall energy transfer was less than 10% of the total fluid stress. The region of greatest energy transfer was located immediately downstream of the constriction. A numerical model of the human larynx was developed using geometry, boundary conditions, and material properties similar to those of the physical model. The numerical results were used to investigate the energy transfer mechanisms between the fluid flow and the structural vibrations. The aerodynamic viscous effects only minimally contributed to the overall energy transfer. The results support the hypothesis that a cyclic variation of the orifice profile from a convergent to a divergent shape leads to a temporal asymmetry in the average wall pressure, which is the key factor for the achievement of self-sustained vocal fold oscillations.
Degree
Ph.D.
Advisors
Frankel, Purdue University.
Subject Area
Mechanical engineering|Biomedical research
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