When breezy, wear masks outdoors to prevent coronavirus exposure
Wind blowing in the same direction as a cough can increase viral
transmission

Date:
October 12, 2021
Source:
American Institute of Physics
Summary:
As the delta variant continues to spread, guidelines from the
CDC recommend even the vaccinated wear masks indoors to prevent
exposure and transmission, though it is less clear what people
should do when outside.

Researchers used a large eddy simulation to model cough jets
in breezy and calm conditions. They found when a person coughs
outdoors, wind flowing in the same direction can propagate the
virus faster over longer distances than in calm conditions.



FULL STORY ==========================================================================
As the highly infectious delta variant of the coronavirus continues to
spread across the United States, guidelines from the Centers for Disease Control and Prevention recommend even the vaccinated wear masks indoors
to prevent exposure and transmission.


========================================================================== However, it is less clear what people should do when outside.

In Physics of Fluids, by AIP Publishing, researchers from the Indian
Institute of Technology Bombay found when a person coughs outdoors,
wind flowing in the same direction can propagate the virus faster over
longer distances than in calm conditions.

"The study is significant in that it points to the increased infection
risk that coughing in the same direction as the wind could bring about," co-author Amit Agrawal said. "Based on the results, we recommend wearing
masks outdoors, particularly in breezy conditions." Other guidelines,
such as coughing in an elbow or turning the face away while coughing,
should be followed to reduce transmission when socializing outdoors.

Most studies model cough flow using puffs of air or a simple pulsating
profile.

But a real cough is more complicated, exhibiting turbulent flow with
prominent vortical structures swirling like mini whirlpools.

To investigate these vortices, the researchers used a large eddy
simulation, a numerical model in computational fluid dynamics that simulatesturbulence. They modeled cough jets in breezy conditions and
in calm conditions representing a typical indoor environment.

These simulations show even a light breeze of about 5 mph extends
effective social distancing by around 20%, from 3-6 feet to 3.6-7.2 feet, depending on cough strength. At 9-11 mph, spreading of the virus increases
in distance and duration.

The researchers found the vortices enable bigger droplets to persist
in the air longer than has been typically assumed, increasing the
time it takes to adequately dilute the viral load in fresh air. As the
cough jet evolves and spreads, it interacts with the wind flowing in
the same direction, and the bigger infected droplets become trapped in
the jet's vortices instead of falling relatively quickly to the ground
under gravity.

"The increase in residential time of some of the larger droplets will
increase the viral load transmitting through the cough jet and, therefore,
the chances of infection," Agrawal said. "Overall, the study highlights increased chances of infection in the presence of even a light breeze." ========================================================================== Story Source: Materials provided by American_Institute_of_Physics. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sachidananda Behera, Rajneesh Bhardwaj, Amit Agrawal. Effect
of co-flow
on fluid dynamics of a cough jet with implications in spread
of COVID-19.

Physics of Fluids, Oct. 12, 2021; DOI: 10.1063/5.0064104 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211012112225.htm

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