NANODROP

The NANODROP project is led by Prof. Stéphane Zaleski from Sorbonne University, France. The goal of the project is to understand the mechanism of COVID's propagation to model and prepare recommendations for protective actions. One of the big problems of the COVID-19 pandemic is a deficit of fundamental knowledge related to generation, transport, and inhalation of pathogen-laden droplets and their pathways as airborne particles, or aerosols, in the transmission between people. In this project, scientists analyse the processes of droplet generation by exhalation, their potential transformation into airborne particles by evaporation, transport over long distances, and inhalation by the receiving host as multiphase flow processes. The team presents a simple model for the time evolution of droplet/aerosol concentration based on a theoretical analysis of the physical processes. The group proposes a better understanding of the transmission of the virus. While gravity causes the larger droplets too quickly fall to the ground, smaller droplets will delay their fall because of viscous drag and air turbulence. They may float long distances through the air making the transmission of diseases by aerosol particles explosive. The group cites anecdotal evidence that bursting surface bubbles in swimming pools produce film drops that propagate viruses in the neighbourhood. It is, however, difficult to estimate the number of such aerosol droplets. Moreover, sneezing is known to spread droplets at distances of more than six meters. These various effects require a better analysis of droplet formation and subsequent dispersion and evolution. The team of Prof. Zaleski, as well as M. Herrmann's group at Arizona, will perform new numerical investigations, and the objective is to prepare useful conclusions on the transmission of SARS by aerosols. This framework along with new experiments and simulations of the group can be used to study a wide variety of scenarios involving breathing, talking, coughing and sneezing and in different environmental conditions, such as humid or dry atmosphere, and confined or open environments. There are still many unresolved issues around evaporation, but with a more reliable understanding of the underlying flow physics of virus transmission, an improved methodology in designing case-specific social distancing and infection control guidelines can be created. For these calculations with the log-conform model of viscoelastic fluid in the basilisk code, PRACE awarded the project with 1 000 000 core hours on Joliot-Curie Rome, hosted by GENCI at CEA, France.