A single cough droplet — under wind speed of two metres per second — can travel up to 6.6 metres and even further under dry air conditions due to droplet evaporation, researchers have found after they incorporated important aspects of fluid physics to deepen the understanding of viral transmission.
In a paper published in the journal ‘Physics of Fluids’, researchers from the Institute of High Performance Computing in Singapore conducted a numerical study on droplet dispersion using high fidelity air flow simulation.
“In addition to wearing a mask, we found social distancing to be generally effective, as droplet deposition is shown to be reduced on a person who is at least one metre from the cough,” said study author Fong Yew Leong.
A typical cough emits thousands of droplets across a wide size range.
The scientists found large droplets settled on the ground quickly due to gravity but could be projected one metre by the cough jet even without wind.
Medium-sized droplets could evaporate into smaller droplets, which are lighter and more easily borne by the wind, and these travelled further.
The researchers offer a more detailed picture of droplet dispersion as they incorporated the biological considerations of the virus, such as the nonvolatile content in droplet evaporation, into the modelling of the airborne dispersion of droplets.
“An evaporating droplet retains the non-volatile viral content, so the viral loading is effectively increased,” said author Hongying Li.
“This means that evaporated droplets that become aerosols are more susceptible to be inhaled deep
into the lungs, which causes infection lower down the respiratory tract, than larger unevaporated droplets”.
The researchers used computational tools to solve complex mathematical formulations representing airflow and the airborne cough droplets around human bodies at various wind speeds and when impacted by other environmental factors.
The findings are hugely dependent on the environmental conditions, such as wind speed, humidity levels.