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

TL;DR

This study uses high-resolution simulations to reveal how turbulence critically influences the dispersion and evaporation of respiratory droplets during violent expiratory events, impacting disease transmission understanding.

Contribution

It introduces a detailed DNS-based analysis showing turbulence's key role in droplet fate, highlighting limitations of coarse-grained models in current research.

Findings

Turbulence significantly affects droplet evaporation times.

Coarse models can have up to 100% errors in predicting droplet behavior.

Droplet inertia combined with turbulence controls evaporation dynamics.

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 (DNS) of the expiratory airflow and a comprehensive Lagrangian model for the droplet dynamics, we identify the key role of turbulence on 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.