  The dispersion of respiratory saliva droplets by indoor wake structures may
enhance the transmission of various infectious diseases, as the wake spreads
virus-laden droplets across the room. Thus, this study analyses the interaction
between vortical wake structures and exhaled multi-component saliva droplets. A
self-propelling analytically-described dipolar vortex is chosen as a model wake
flow, passing through a cloud of micron-sized evaporating saliva droplets. The
droplets' spatial location, velocity, diameter, and temperature are traced and
coupled to their local flow field. For the first time, the wake structure decay
is incorporated and analyzed, which is proved essential for accurately
predicting the settling distances of the dispersed droplets. The model also
considers the non-volatile saliva components, adequately capturing the essence
of droplet-aerosol transition and predicting the equilibrium diameter of the
residual aerosols. Our analytic model reveals non-intuitive interactions
between wake flows, droplet relaxation time, gravity, and transport phenomena.
We reveal that given the right conditions, a virus-laden saliva droplet might
translate to distances two orders of magnitude larger than the carrier-flow
characteristic size. Moreover, accounting for the non-volatile contents inside
the droplet may lead to fundamentally different dispersion and settling
behavior compared to non-evaporating particles or pure water droplets. Ergo, we
suggest that the implementation of more complex evaporation models might be
critical in high-fidelity simulations aspiring to assess the spread of airborne
respiratory droplets.
