DNS of Aerosol Particle Spreading Emitted by Coughing and Breathing in a Simplified Room

Besides coughing and sneezing, breathing is the most frequent particle emission event of aerosol droplets carrying the SARS-COV-2 virus or viruses of other airborne diseases. Direct Numerical Simulations (DNS) of ‘jet-like’ emissions of particle clouds through the mouth caused by coughing and breathing are performed in a cuboidal simplified room to study the spreading of respiratory droplets with different momentum and size. Contrary to coughing, we found that no droplet follows a ballistic trajectory after a breathing event since all the droplets are trapped in the humid puff of air. The detailed analysis and the comparison of the predictions obtained for respiratory droplets emitted by single breathing and coughing events are further discussed. Despite the major difference between the maximum exhalation speeds reached during coughing and breathing, the horizontal propagation distance differs by less than 30%. Additionally, a comparison of the results of the present DNS neglecting aerosol evaporation and considering buoyancy forces with the results of an earlier DNS study from the literature taking evaporation into account but neglecting buoyancy, revealed that buoyancy damps the horizontal propagation of the humid puff and enhances the upward motion.