Role of pulsatility on particle dispersion in expiratory flows

TL;DR

This study uses direct numerical simulation to analyze how pulsatility in expiratory flows affects respiratory particle dispersion, revealing that increased pulsatility hinders overall dispersion but enhances penetration from secondary pulses.

Contribution

It introduces a novel DNS-based approach to model pulsatile expiratory jets and examines the effects of multiple pulses on particle dispersion and penetration.

Findings

Increased pulsatility hinders overall particle dispersion.

Secondary and tertiary pulses enhance particle penetration due to vortex acceleration.

Multiple pulses alter the evolution of particle clouds compared to single-pulse models.

Abstract

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.