Scientists to Unlock the Mystery of Airborne Fluid Droplets Containing COVID-19

Scientists are working to unlock the mystery of fluid dynamics and how COVID-19 transmission works between people coughing, sneezing, or touching similar surfaces.
Brad Bergan

More than a century following the Spanish flu's 50-million-person death toll, the motion of exhaled fluid droplets carrying infectious diseases has remained largely unknown, but scientists are working to study the flow physics of respiratory diseases — and think it will be key to containing the COVID-19 illness, according to a study published in Cambridge University's Journal of Fluid Mechanics.


COVID-19 fluid dynamics and transmission

Public health experts haven't changed the standard advice for evading respiratory illness since the Spanish flu of 1918 — one of the worst pandemics in history. The basics are the same: keeping a safe distance from people, washing hands with soap and water to eliminate germs, and covering one's nose and mouth with a face mask (bandanas work). But even now, much of how fluid droplets behave remains a mystery, according to

Professor of Mechanical Engineering at the Whiting School of Engineering with an emphasis in computational fluid dynamics thinks more research into fluid droplets in the context of coronavirus transmission will be of crucial importance in fighting the pandemic.

Jung-Hee Seo / Cambridge University
Animated simulation of expelled droplets potentially containing infectious diseases. Source: Jung-Hee Seo / Cambridge University

Fluid dynamics in the grocery store

The idea first struck Mittal while on run through his grocery store, where he observed shoppers donning protective masks. And his thoughts went to a place where researchers' minds usually go when confronted with something new: science.

"I started wondering if there's any data out there about the aerodynamics of these masks to quantify what they are really doing," said Mittal. "As I started to dive into the literature, it became clear that fluid dynamics intersects with nearly every aspect of this pandemic. How droplets are formed and carried, how they infect others, the ventilators we use to treat patients with this disease, even preventative measures like face masks — many of these problems are ultimately related to fluid flow."

To help move thinking consensus forward in this area, Mittal and a team of his faculty colleagues compiled an analysis of the known fluid dynamics of COVID-19 and what questions still go unanswered.

COVID-19 transmission via droplets

Respiratory infections can spread between people via virus-carrying droplets that move through the air, or spread by contact with droplet-contaminated surfaces. Infected people often expel the droplets via sneezing or coughing — a classic sign for others to evade infection. However, the reality of transmission is more complex and involves the number of droplets, their size, and velocity during expiratory events like breathing, sneezing, and coughing.

Sneezing might expel thousands of large droplets at high relative velocity, whereas coughing creates 10 to 100 times fewer droplets. Speaking expels far fewer droplets — at about 50 per second, they are also smaller. These droplets are likely to suspend in the air, travel farther through the air, and transmit COVID-19 infection once inhaled. Larger droplets, however, are more likely to leave surfaces contaminated and spread infection via tactile touch.

Since the fluid nature of this phenomenon is very complex, the consensus surrounding droplet behavior amid COVID-19 remains elusive.

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