Turbulence role in the fate of virus-containing droplets in violent expiratory events

Abstract

Violent expiratory events, such as coughing and sneezing, are highly nontrivial examples of a two-phase mixture of liquid droplets dispersed into an unsteady turbulent airflow. Understanding the physical mechanisms determining the dispersion and evaporation process of respiratory droplets has recently become a priority given the global emergency caused by the SARS-CoV-2 infection. By means of high-resolution direct numerical simulations (DNSs) of the expiratory airflow and a comprehensive Lagrangian model for the droplet dynamics, we identify the key role of turbulence in the fate of exhaled droplets. Due to the considerable spread in the initial droplet size, we show that the droplet evaporation time is controlled by the combined effect of turbulence and droplet inertia. This mechanism is clearly highlighted when comparing the DNS results with those obtained using coarse-grained descriptions that are employed in the majority of the current state-of-the-art investigations, resulting in errors up to 100% when the turbulent fluctuations are filtered or completely averaged out.