Detailed simulation of air flow after sneezing to study the transmission of diseases

The team used high-performance computing systems to simulate the flow of air generated by sneezing. These results provide a better understanding of the ability of infectious aerosols in the environment to disperse and remain suspended. At the start of April 2021, more than 130,000,000 people had been infected by the COVID-19 pandemic. More than 2.8 million of them died. SARS-CoV-2 is responsible for COVID-19. It transmits especially via aerosols and droplets that are released when someone coughs, speaks, sneezes, or coughs. When viruses or other pathogens are inhaled, they spread throughout the environment and can transmit infectious diseases to others. These particles' ability to stay suspended in the atmosphere and spread throughout the environment is dependent on how large and how clean the airflow generated by the exhaustion of air. Fluid dynamics plays a key role in predicting the possibility of infection from inhaling suspended particles. A coughing episode that lasts 0.4 seconds has an exhaled speed of 4.8m/s. The flow first creates a turbulent stream that is more humid and hotter than the surrounding environment. After expiration, the stream becomes a puff of air. It rises due to flotation and lack of weight as it dissipates. Clouds are formed when particles move through this flow. Their trajectories depend on the size of the particles. Gravity governs the dynamics of large particles and describes parabolas that have a clear horizontal limit. Despite their inability to stay suspended and the limited horizontal range, viral loads can be very high due to their large size (diameters greater than 50 microns). The action of airflow transports the smallest particles, with diameters less than 50 microns. These aerosols can stay suspended for longer periods of time and spread more widely. While the largest particles can stay suspended in the air for only a few seconds, the smallest particles can be kept suspended for several minutes. When the particles are smaller, the retention percentage of facemasks decreases. The behavior of the cloud of particles depends on their size. Evaporation can also affect the behaviour of the cloud. This reduces the droplets' diameter gradually. The Consortium of University Services of Catalonia supported the research group from the URV's Department of Mechanical Engineering. Jordi Pallars and Alexandre Fabregat, along with researchers from the University of Utah, have used high-performance numerical simulations in order to investigate in unprecedented detail the aerosol dispersion caused by a cough. They needed a lot of calculation power and many processors to run the simulations simultaneously. The plume of air generated by expiration contains particles less than 32 microns high. This results in a cloud with a large capacity to stay suspended and be dispersed over considerable distances by air currents. The largest particles are limited in scope and this is not affected by evaporation. The results of the study were used to determine the average viral load for infectious diseases. They also helped to create a map showing the concentration of viruses around infected people after they had coughed and sneezed. The journal Physics of Fluids published two scientific papers based on this research. They are entitled "Direct numerical simulating turbulent flow during an intense expiratory event" (numbers 1-2) and "Direct numerical simulating turbulent dispersion of aerosol clouds caused by an intense expiratory incident". Because of their scientific importance, both articles were included on the front cover. ### Refer to: Alexandre Fabregat and Ferran Gisbert, Anton Vernet and Josep Anton Ferr, "Direct numerical simulation of turbulent dispersion of aerosol clouds formed by an intense expiratory events", Physics of Fluids 33. 033329 (2021). https:// doi. 1063/ 5. 1063/ 5. 1063/ 5.


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