Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Mechanical and Materials Engineering

Supervisor

Zhang, Chao

2nd Supervisor

Savory, Eric

Co-Supervisor

Abstract

As part of the Western Cold and Flu aerosol (WeCoF) studies, the present study provides Computational Fluid Dynamics (CFD) modelling of human cough flow. The cough flow is characterized in two different aspects, the flow field and the droplets. In the study of the flow field of coughing, various dynamic characteristics, including the velocity variation, streamwise penetration and power spectral density, are examined. CFD simulations using two different approaches, the unsteady Reynolds Averaged Navier-Stokes (URANS) and the large eddy simulation (LES), are performed for comparison purposes. The numerical results are validated by the experimental data obtained from the measurements by the particle image velocimetry (PIV) and hot-wire anemometry (HWA), as well as the published data. Based on the comparison with the URANS approach and the experimental data, the LES approach can be considered as a good candidate to predict the flow field of coughing.

In the study of the droplets produced by coughing, the dynamic characteristics, including the dispersion and evaporation processes, are analyzed. The Lagrangian discrete phase model is adopted to track a total 2084 droplets in the diameter range 3-750 μm. The effects of the relative humidity (RH) of the ambient air and the inlet time-dependent cough velocity on the dispersion and evaporation of the droplets are investigated. It is found that the larger droplets precipitate on the ground as the time progresses, and the precipitating speed depends on the droplet size, whereas the smaller droplets with the diameter dp ≤ 10 μm remain suspended for a longer period. The dispersion process in terms of the droplet penetration is weakened by both a higher ambient RH and a lower inlet cough velocity. The droplet evaporation is significantly affected by the ambient RH, i.e. the higher the RH, the slower the evaporation. However, the inlet cough velocity doesn’t show a strong influence on the evaporation of the droplets.

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