A study of fluid dynamics and human physiology factors driving droplet dispersion from a human sneeze

Abstract

Recent studies have indicated that COVID-19 is an airborne disease, which has driven conservative social distancing and widescale usage of face coverings. Airborne virus transmission occurs through droplets formed during respiratory events (breathing, speaking, coughing, and sneezing) associated with the airflow through a network of nasal and buccal passages. The airflow interacts with saliva/mucus films where droplets are formed and dispersed, creating a route to transmit SARS-CoV-2. Here, we present a series of numerical simulations to investigate droplet dispersion from a sneeze while varying a series of human physiological factors that can be associated with illness, anatomy, stress condition, and sex of an individual. The model measures the transmission risk utilizing an approximated upper respiratory tract geometry for the following variations: (1) the effect of saliva properties and (2) the effect of geometric features within the buccal/nasal passages. These effects relate to natural human physiological responses to illness, stress, and sex of the host as well as features relating to poor dental health. The results find that the resulting exposure levels are highly dependent on the fluid dynamics that can vary depending on several human factors. For example, a sneeze without flow in the nasal passage (consistent with congestion) yields a 300% rise in the droplet content at 1.83 m (≈6 ft) and an increase over 60% on the spray distance 5 s after the sneeze. Alternatively, when the viscosity of the saliva is increased (consistent with the human response to illness), the number of droplets is both fewer and larger, which leads to an estimated 47% reduction in the transmission risk. These findings yield novel insight into variability in the exposure distance and indicate how physiological factors affect transmissibility rates. Such factors may partly relate to how the immune system of a human has evolved to prevent transmission or be an underlying factor driving superspreading events in the COVID-19 pandemic.

Direct numerical simulation of the turbulent flow generated during a violent expiratory event

“…Fontes et al also used numerical simulations to investigate the fluid dynamics of a sneeze. 13 In particular, they focused on the impact of human physiological factors (e.g., illness, stress condition, anatomy, etc.) on droplet dispersion.…”

Direct numerical simulation of turbulent dispersion of evaporative aerosol clouds produced by an intense expiratory event

“…The impact of human physiological factors (e.g., illness, stress condition, and anatomy) was addressed by Fontes et al who used numerical simulations to simulate a sneeze. 37 These authors modeled the carrier phase under the Eulerian framework using Detached Eddy Simulations (DES) with a hybrid solver that combined unsteady Reynolds Averaged Navier–Stokes (URANS) for the flow within the boundary layer and Large Eddy Simulations (LES) in the outer region. Again, droplets were assumed to be Lagrangian particles.…”

Jet fans in the underground car parking areas and virus transmission

“…Smith et al 40 modeled the dynamics of exhaled respiratory droplets to account for the aerosol persistence times in confined public environments. Fontes et al 41 presented the numerical analysis of the effect of human physiology factors on the respiratory droplet transmission of SARS-CoV-2. They showed that an ill host may be less likely to transmit a pathogen when they frequently blow their nose.…”