Numerical study of spread of coughing droplets by human walking and indoor wind environment

Abstract

Indoor ventilation and human movement are important factors affecting the spread of droplets. In this paper, the effects of indoor wind speed and human movement on the propagation and diffusion of cough ejected droplets are investigated using computational fluid dynamics. The effects of cough non-isothermal jet flow, indoor wind velocity, and human movement on the transmission of exhaled droplets were studied. The droplet size ranges in dynamic indoor environments were redefined based on the risk of droplet spread dispersal. The buoyant flux, gravity, inertial forces, and drag forces that affect the droplet motion were evaluated. The results show that droplet spread above 40 μm is limited by indoor airflow or human-induced wake and settles rapidly under the influence of gravity. The indoor air velocity makes the droplets of less than 40 μm to spread within 4 m in front of the cougher within 18 s. The induced wake allowed the lateral movement of droplets between the coughing person and the moving person, but the diffusion effect was much less than the effect of indoor air velocity. The combined effect of indoor air velocity and human movement makes the indoor flow field very complex. It greatly delays the deposition time of 10–40 μm droplets (2.2 times) and makes droplets below 10 μm to spread rapidly to distant locations by the induced wake, increasing the risk of infection. Further research is required to quantify the influence of parameters, such as the human movement and evaporation of droplets among others in indoor dynamic environment.