A numerical assessment of social distancing of preventing airborne transmission of COVID-19 during different breathing and coughing processes

Abstract

The spread of the novel coronavirus disease (COVID-19) continues to show that geographic barriers alone cannot contain the virus. Asymptomatic carriers play a critical role in the nature of this virus, which is rapidly escalating into a global pandemic. Asymptomatic carriers can inadvertently transmit the virus through the air stream. Many diseases can infect human bodies with tiny droplets or particles that carry various viruses and bacteria that are generated by the respiratory system of infected patients. This article presents the numerical results of the spread of droplets or particles in a room. The proposed numerical model in this work takes into account the sedimentation of particles or droplets under the action of gravitational sedimentation and transport in the room during the process of breathing and sneezing or coughing. Three different cases are numerically investigated taking into account normal breathing and coughing or sneezing, respectively, and three different rates of particle ejection from the mouth are considered. Navier–Stokes equations for incompressible flows were used to describe three-dimensional air flow inside ventilated rooms. The influence of ventilation rate on social distancing is also computationally investigated. It was found that particles can move up to 5 m with a decrease in concentration in the direction of the air flow. The conclusions made in this work show that, given the environmental conditions, the two meter social distance recommended by WHO is insufficient.

Evaporation flow characteristics of airborne sputum droplets with solid fraction: Effects of humidity field evolutions

“…In order to develop a mathematical model of the droplet dynamics in a turbulent airflow exhaled from the mouth, the incompressible Navier–Stokes equations system is used to model the ambient airflow field. 1–5 Considered with the tiny suspended aerosols (diameters smaller than the Kolmogorov scale 20 ) the collisions between droplets and the force feedback on the airflow can be ignored. 2,3,21 The continuity and momentum equations used in this model are defined as follows: where u f (m/s), ρ f (kg/m 3 ), and p (Pa) represent the velocity, density and pressure field, respectively, and μ f (Pa·s) is dynamic viscosity coefficient of airflow.…”

“… 2,17 The moving airflow mixes with the air, and gradually becomes unsaturated. The advection-diffusion equation is used to describe the evolution of supersaturation field, 1,3,22 which is written as where φ (= RH − 1) is supersaturation field, and D d is the water vapor diffusion coefficient. The fluctuations of supersaturation are produced inside the cloud by the turbulent velocity field acting on the vertical gradient of humidity sustained by temperature.…”

“…The COVID-19 pandemic has attracted scientific attention to the mechanism of the transportation of airflow and the ejection of aerosols from the respiratory tract through coughing, sneezing, and breathing. 1–6 Exhalation produces many turbulent clouds (including tiny droplets) with limited momentum, kinetic energy, and thermal energy, moving as a viscous fluid at an unstable drift velocity. These aerosols, which carry a small mass fraction of solid/protein/salt components, are transported or suspended in the air.…”

Natural Ventilation in Urban Buses: From Negative Pressure To Velocity-Driven Dispersion of Aerosols

“…It is important to mention that ventilation quality or removal of pollutants from indoor spaces have also been studied computationally in other kind of public spaces; relevant examples include the flow characteristics and motion of airborne species inside an aircraft cabin 23,24 , the flow inside a high speed train cabin 25 and inside an automobile 26 (these authors also noticed the aforementioned back-to-front pumping effect); flow and aerosol dispersion inside a conference room, 27 inside a generic ventilated room 28 , a supermarket 29 or a restaurant 30 , and the flow inside buildings and hospitals (see Ref. 31 for a general review on the subject).…”

Effectiveness of Infection Preventive Behaviors on COVID-19-Like Illness Symptoms During the Winter Third Wave of the Epidemic in Japan: A 2-Month Follow-up Nationwide Cohort Study

“…8 In addition, small droplets have been reported to be a possible cause of aerosol transmission. 9,10 At least until COVID-19 vaccines are widely available and reliable treatment methods are fully established, multilayered non-pharmaceutical intervention (NPI) strategies should be adopted to reduce SARS-CoV-2 transmission; such NPIs should include preventive behaviors such as wearing face masks, practicing hand hygiene, and ensuring proper room ventilation. 11…”