Role of Pulsatility on Aerosol Dispersion in Expiratory Flows

With an expected second wave of COVID 19 in the near future, there is an immediate need to develop a better understanding of factors contributing to dispersion of contagion carrying droplets during expiratory events. Although single-pulse expiratory events have been widely studied in the past, this work seeks to quantify the effects of pulsatility (multiple expulsions during a single event) on the underlying flow physics. We hypothesize that a pulsatile jet (mimicking for example a real cough or continuous speech) could increase entrainment and carry droplets farther than a single puff of turbulent jet due to vortex-vortex interactions. In this talk, direct numerical simulations (DNS) of turbulent pulsatile jets coupled with Lagrangian particle tracking of micron-sized droplets will be presented to investigate the role of secondary and tertiary expulsions on aerosol dispersion. Flow developing in the trachea is first approximated by DNS of a fully-developed turbulent pipe flow laden with 10-micron droplets and then utilized as an inflow boundary condition when examining pulsatility. The volumetric flowrate of the incoming turbulence is modulated according to a damped sine wave that controls the number of pulses, its duration, and peak amplitude.