Numerical investigation of respiratory drops dynamics released during vocalization

Abstract

Release of drops from a human body has been the focus of many recent investigations because of the current COVID-19 pandemic. Indirect virus transmission from asymptomatic individuals has been proved to be one of the major infectious routes and difficult to quantify, detect, and mitigate. We show in this work a detailed and novel numerical investigation of drops released during vocalization from a thermal manikin using a large eddy simulation coupled with Lagrangian tracking of drops. The vocalization experiment was modeled using existing data from the literature for modeling exhaled airflow, emission rate, and size distribution. Particular focus was on the definition of the boundary conditions for the exhalation process. Turbulence was compared with experimental data for the near mouth region for 75 exhalation breathing cycles and showed the sensitivity of different modeling assumptions at the mouth inlet. The results provide insights of special interest for understanding drop dynamics in speech-like exhalation modes, modeling the mouth inlet boundary conditions, and providing data for verifying other more simplified models.

Numerical investigation of droplets in a cross-ventilated space with sitting passengers under asymptomatic virus transmission conditions

“…The computational fluid dynamics (CFD) modeling used in this work is similar to the one described by Peña-Monferrer et al 91 The reader is also referred to the extensive literature describing the methods used in this work. 92,93 The reactingParcelFoam OpenFOAM v2012 94 solver was used, which allowed us to compute in an Eulerian–Lagrangian framework, a transient, turbulent, compressible, multi-species, and multiphase particle cloud scenario.…”

“…To represent turbulent fluctuations in an LES, we use the divergence-free synthetic eddy method (DFSEM) of Poletto et al 106 for generating correlated, turbulence-like perturbations with a turbulence intensity at the mouth of 0.16. Similar to Peña-Monferrer et al , 91 we use the turbulence intensity to compute the Reynolds stresses and define the off diagonal Reynolds stress components as negligible.…”

“…The particles were seeded at the patch representing the mouth openings with a defined particle rate of 41 particles per second and a lognormal size distribution with mean 0.6951 μ m and standard deviation 0.7577 μ m. These values were obtained from the measurements by Asadi et al 104 for the fundamental frequency of F 0 250 Hz. Further details about the BCs employed for the exhalation are described by Peña-Monferrer et al 91 …”

“…The asymptomatic virus transmission condition is represented using the approach described by Peña-Monferrer et al 91 for modeling the vocalization of vowel /ɑ/ applied to the conditions of a given female subject. This reference used experimental data to define the exhaled velocity, size distribution, and particle rate applied to a thermal manikin in a mockup.…”

“…Different inlet BC approaches were evaluated considering spatial and turbulent effects at the inlet, and fluid dynamics were validated with experimental data. The conditions in Peña-Monferrer et al 91 are used in this work for reproducing a speech-like exhalation mode in a cross-ventilated space with passengers.…”