Effects of turbulence and vortical structures on aerosolized droplets during speaking

One of the main transmission routes of respiratory diseases is spread by the generation and aerosolization of virus-laden respiratory droplets. While the concentration of respiratory droplets is large for a cough or sneeze, talking—over time—can yield similar numbers of droplet nuclei but different droplet size distributions. Geometrically-resolving, large-eddy simulations incorporating a model geometry of the mouth and throat are undertaken to capture the expulsion of aerosolized droplets during speaking over a range of parameters, including Reynolds number, concentration, and size distribution. The trajectories of the droplets coupled with temperature and relative humidity are tracked. Simulation results are validated with experimental measurements of the concentration of droplets detected downwind of the mouth of a human, speaking. Statistics of droplet motion with respect to the background flow reveal that droplet trajectory is influenced by turbulent fluctuations and regions of high vorticity. This can affect the inertia and lifetime of expelled droplets.