Modeling and validation of auto-oscillation onset in a constricted tube with application to phonation

An experimental study of the auto-oscillation onset is performed for airflow in a rigid tube containing a constriction downstream from a deformable portion as a function of the constriction degree. A quasi-one dimensional laminar flow model in combination with a reduced order mechanical model (symmetric two mass model) provides a physical fluid-structure interaction model of the deformable portion. Mechanical, geometrical and flow model parameters are chosen to match the experimental setup. Modeled as well as experimental results show that a severe constriction (>80%) at first hinders (≥89%) and eventually inhibits (≥95%) auto-oscillation. Constrictions of different severity occur naturally in voiced speech sound production (phonation) due to articulation. The current study provides quantitative evidence of the role of the vocal tract constriction degree as a control parameter for phonation (voiced speech sound production) since increasing the constriction degree decreases the vocal folds oscillation frequency (decrease by 25%) and increases the minimum pressure needed to initiate oscillation (increase by 80%).