Abstract
Human respiratory events, such as coughing and sneezing, play an important role in the host-to-host airborne transmission of diseases. Thus, there has been a substantial effort in understanding these processes: various analytical or numerical models have been developed to describe them, but their validity has not been fully assessed due to the difficulty of a direct comparison with real human exhalations. In this study, we report a unique comparison between datasets that have both detailed measurements of a real human cough using spirometer and particle tracking velocimetry, and direct numerical simulation at similar conditions. By examining the experimental data, we find that the injection velocity at the mouth is not uni-directional. Instead, the droplets are injected into various directions, with their trajectories forming a cone shape in space. Furthermore, we find that the period of droplet emissions is much shorter than that of the cough: experimental results indicate that the droplets with an initial diameter ≳10μm are emitted within the first 0.05 s, whereas the cough duration is closer to 1 s. These two features (the spread in the direction of injection velocity and the short duration of droplet emission) are incorporated into our direct numerical simulation, leading to an improved agreement with the experimental measurements. Thus, to have accurate representations of human expulsions in respiratory models, it is imperative to include parametrisation of these two features.
Highlights
Since the outbreaks of SARS-CoV in 2003 and SARS-CoV-2 in 2019, the role played by the turbulent multiphase flow in the transmission of infectious diseases via the airborne route has received increasing attention
The numerical dataset is obtained using direct numerical simulations (DNS) based on the methods employed by Chong et al (2021) and Ng et al (2021), and the experimental component is the extension of the method used by Bahl et al (2020) to coughs
Incorporating the short droplet emission time in the model can significantly improve the agreement between the simulation and the experiment
Summary
Since the outbreaks of SARS-CoV in 2003 and SARS-CoV-2 in 2019, the role played by the turbulent multiphase flow in the transmission of infectious diseases via the airborne route has received increasing attention. The Wells–Riley model centres on the concept of ‘quantum’, which is the dose required to start an infection, while the dose–response model uses the amount of pathogen taken in by the susceptible individual In both approaches, the complicated transmission process that involves a series of stages (exhalation, dispersion, ventilation, inhalation, etc.) is parametrised based on some physical assumptions or empirical observations (Lelieveld et al, 2020; Bazant and Bush, 2021; Jones et al, 2021; Nordsiek et al, 2021). The numerical dataset is obtained using direct numerical simulations (DNS) based on the methods employed by Chong et al (2021) and Ng et al (2021), and the experimental component is the extension of the method used by Bahl et al (2020) to coughs We reveal that both the droplet emission duration and the initial spread angle have strong influence on the far-field behaviour of the flow field.
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