Trajectories of Evaporating Microdroplets in Unsteady Flow in Respiratory Airways

Airborne disease transmission by respiratory droplets became the focus of many experimental and computational studies after millions of lives were impacted by the COVID-19 pandemic. One of the important topics in the field involves inhaled droplet trajectories and deposition behavior in human respiratory airways. In the present study, we extend our previous work on droplet motion in steady flow to investigate the trajectories and deposition patterns in unsteady laminar flows generated during inhalation. Our approach relies on modification of the classical boundary layer models to account for both spatial and time-dependent variations of the flow field. We take into account evaporation from both the droplet surface and the mucus-covered airway wall where the droplet is eventually deposited. Detailed parametric studies are conducted to illustrate how the unsteady nature of the flow affects droplet deposition patterns.