We provide research findings on the physics of aerosol and droplet dispersion relevant to the hypothesized aerosol transmission of SARS-CoV-2 during the current pandemic. We utilize physics-based modeling at different levels of complexity, along with previous literature on coronaviruses, to investigate the possibility of airborne transmission. The previous literature, our 0D-3D simulations by various physics-based models, and theoretical calculations, indicate that the typical size range of speech and cough originated droplets ( ) allows lingering in the air for ) so that they could be inhaled. Consistent with the previous literature, numerical evidence on the rapid drying process of even large droplets, up to sizes , into droplet nuclei/aerosols is provided. Based on the literature and the public media sources, we provide evidence that the individuals, who have been tested positive on COVID-19, could have been exposed to aerosols/droplet nuclei by inhaling them in significant numbers e.g. . By 3D scale-resolving computational fluid dynamics (CFD) simulations, we give various examples on the transport and dilution of aerosols ( ) over distances in generic environments. We study susceptible and infected individuals in generic public places by Monte-Carlo modelling. The developed model takes into account the locally varying aerosol concentration levels which the susceptible accumulate via inhalation. The introduced concept, ’exposure time’ to virus containing aerosols is proposed to complement the traditional ’safety distance’ thinking. We show that the exposure time to inhale aerosols could range from to or even to depending on the situation. The Monte-Carlo simulations, along with the theory, provide clear quantitative insight to the exposure time in different public indoor environments.

No abstract

No abstract

A computational fluid dynamics study is carried out on the inner nozzle flow and onset of liquid sheet instability in a large-scale pressure-swirl atomizer with asymmetric inflow configuration for high viscosity fluids. Large-eddy simulations (LES) of the two-phase flow indicate the unsteady flow character inside the nozzle and its influence on liquid sheet formation. A novel geometric volume-offluid (VOF) method by Roenby et al., termed isoAdvector, is applied for sharp interface capturing (Roenby J., Bredmose H., Jasak H., 2016, A computational method for sharp interface advection, Royal Society Open Science 3). We carry out a Reynolds number sweep (420 ≤ Re ≤ 5300) in order to investigate the link between the asymmetric inner nozzle flow and liquid sheet characteristics in laminar, transitional and fully turbulent conditions. Inside the nozzle, the numerical simulations reveal counter-rotating Dean vortices, flow impingement locations, and strong asymmetric flow features at all investigated Reynolds numbers. A helical, rotating gaseous core is observed when Re ≥ 1660. For laminar flow (Re = 420), an S-shaped liquid film is observed, while the gas core presence at Re ≥ 1660 results in a hollow cone liquid sheet. For the intermediate value Re = 830, the numerical simulations indicate a liquid sheet of mixed type.

Computational fluid dynamics investigations on the mixing process of gases inside an atomic layer deposition (ALD) reactor are carried out. A test case involving a real ALD reactor geometry is investigated under nonreacting, incompressible flow assumption. The relatively low Reynolds number (Re) of the test reactor, often being in the laminar regime, advocates the usage of scaleresolving simulations. The authors investigate mixing of two precursors in two different injection configurations for 40 < Re < 2400. The feasibility of the approach is shown and discussed. The results illustrate how both Reynolds number and injection configurations influence the precursor distribution in the ALD reactor. The authors also carry out a set of experiments in the same ALD reactor and discuss them in light of the simulations.