CFD analysis of mucus bridge instability and breakup in the vocal folds

The atomization of airway mucus during speech represents a primary mechanism for respiratory aerosol generation, which is central to airborne pathogen transmission. While extensive research has examined single-phase phonation aerodynamics, the multiphase dynamics of droplet formation has received less attention. This study aims to fill this critical gap by presenting a multiphase computational fluid dynamics (CFD) model of the human vocal folds. The dynamic formation and subsequent breakup of the mucus bridge are simulated using a volume-of-fluid method coupled with an analytical model describing the time-dependent shape of the glottal orifice. The investigation reveals that initial, small-scale stochastic perturbations on the mucus surface are essential for triggering a physically realistic, multimodal breakup, in contrast to the delayed, symmetric rupture observed in idealized smooth-film simulations. During vocal-folds opening, the bridge thickness exhibits exponential decay rupturing after 2.32 ms at a dynamic aspect ratio of approximately 20, a value significantly exceeding the static stability limit. Furthermore, a parametric study reveals that increasing transglottal pressure from 491 Pa to 1472 Pa , corresponding to louder phonation, accelerates the thinning process and leads to earlier initial rupture after 2.04 ms . This work provides fundamental insights into the precursors of respiratory aerosol generation