WASHINGTON, December 15, 2020 – Computational simulations have been used to accurately predict airflow and droplet dispersion patterns in situations where COVID-19 could be widespread. In the diary Fluid physics, from AIP Publishing, the results show the importance of space shape in modeling how virus-laden droplets move through the air.
Simulations are used to determine the flow patterns behind an individual walking into spaces of different shapes. The results reveal a higher risk of transmission for children in some cases, such as behind people moving quickly in a long, narrow corridor.
Previous investigations using this simulation technique have helped scientists understand the influence of objects, such as glass barriers, windows, air conditioners and toilets, on airflow patterns and the spread of the virus. Previous simulations have usually assumed a large, open interior space but have not considered the effect of neighboring walls, such as those that might exist in a narrow corridor.
If a person walking down a corridor coughs, their breath expels droplets that travel around and behind their body, forming a trail the way a boat makes a trail in the water as it travels. The investigation revealed the existence of a “recirculation bubble” directly behind the person’s torso and a long trail running behind them at about waist height.
“The flow patterns we found are strongly related to the shape of the human body,” said author Xiaolei Yang. “At 2 meters downstream, the trail is almost negligible at the height of the mouth and leg but is still visible at the waist”.
Once the airflow patterns were determined, the investigation modeled the dispersion of a cloud of droplets ejected from the simulated person’s mouth. The shape of the space surrounding the moving person is particularly critical for this part of the calculation.
Two types of dispersion modes were found. In one mode, the droplet cloud detaches from the moving person and floats a lot behind that person, creating a floating bubble of virus-laden droplets. In the other mode, the cloud is attached to the person’s back, trailing behind them like a tail as they move through space.
“For the detached mode, the droplet concentration is much higher than in the connected mode, five seconds after a cough,” Yang said. “This poses a great challenge in determining safe social distance in places like a very narrow corridor, where a person can inhale viral droplets even if the patient is far in front of him or her.”
The danger is particularly serious for children, since in both modes the cloud of droplets hovers at a distance from the ground that is about half the height of the infected person, in other words at the level of the children’s mouth.
The article, “Effects of space size on the scattering of cough droplets from a walking person,” is written by Zhaobin Li, Hongping Wang, Xinlei Zhang, Ting Wu and Xiaolei Yang. The article will appear in Fluid physics on 15 December 2020 (DOI: 10.1063 / 5.0034874).
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