  The Coronavirus disease outbreak of 2019 has been causing significant loss of
life and unprecedented economical loss throughout the world. Social distancing
and face masks are widely recommended around the globe in order to protect
others and prevent the spread of the virus through breathing, coughing, and
sneezing. To expand the scientific underpinnings of such recommendations, we
carry out high-fidelity computational fluid dynamics simulations of
unprecedented resolution and realism to elucidate the underlying physics of
saliva particulate transport during human cough with and without facial masks.
Our simulations: (a) are carried out under both a stagnant ambient flow
(indoor) and a mild unidirectional breeze (outdoor); (b) incorporate the effect
of human anatomy on the flow; (c) account for both medical and non-medical
grade masks; and (d) consider a wide spectrum of particulate sizes, ranging
from 10 micro m to 300 micro m. We show that during indoor coughing some saliva
particulates could travel up to 0.48 m, 0.73 m, and 2.62 m for the cases with
medical-grade, non-medical grade, and without facial masks, respectively. Thus,
in indoor environments either medical or non-medical grade facial masks can
successfully limit the spreading of saliva particulates to others. Under
outdoor conditions with a unidirectional mild breeze, however, leakage flow
through the mask can cause saliva particulates to be entrained into the
energetic shear layers around the body and transported very fast at large
distances by the turbulent flow, thus, limiting the effectiveness of facial
masks.
