  Expiratory events, such as coughs, are often pulsatile in nature and result
in vortical flow structures that transport respiratory particles. In this work,
direct numerical simulation (DNS) of turbulent pulsatile jets, coupled with
Lagrangian particle tracking of micron-sized droplets, is performed to
investigate the role of secondary and tertiary expulsions on particle
dispersion and penetration. Fully-developed turbulence obtained from DNS of a
turbulent pipe flow is provided at the jet orifice. The volumetric flow rate at
the orifice is modulated in time according to a damped sine wave; thereby
allowing for control of the number of pulses, duration, and peak amplitude. The
resulting vortex structures are analyzed for single-, two-, and three-pulse
jets. The evolution of the particle cloud is then compared to existing
single-pulse models. Particle dispersion and penetration of the entire cloud is
found to be hindered by increased pulsatility. However, the penetration of
particles emanating from a secondary or tertiary expulsion are enhanced due to
acceleration downstream by vortex structures.
