Influence of Thermal Plume on Cough-Generated Droplet Aspiration and Deposition in the Airway Under Unsteady Breathing

This study deals with numerical simulations of single-cough event airflow and cough-generated droplet inhalation and deposition in an airway under unsteady breathing conditions. A (healthy) receptor mannequin with an attached airway from the nostril inlet to the end of the 4th lung generation was placed face-to-face with an (infected) cougher mannequin at a distance of 0.5 m. Two cases with and without thermal plumes around the mannequins were considered for airflow in the room. An unsteady cyclic breathing pattern with a duration of 5.4 s, equivalent to a steady breathing flow rate of 20 lit/min, was assumed for the receptor mannequin respiration. For numerical simulations, 4 receptors’ breathing cycles corresponding to 21.6 s were simulated. The coughing event with 0.42 s duration starts at 10.37 s after receptor mannequin breathing, corresponding to 4.97 s after the start of the second breathing cycle. The low Reynolds SST k-ω turbulence model was used to simulate the airflow field using Ansys-Fluent software. The motion of cough droplets was simulated with the Lagrangian approach. A user-defined function (UDF) was employed for the stochastic modeling of turbulence fluctuations coupled with the Ansys-Fluent discrete phase model. For particle tracking, 106,470 spherical droplets with 2, 5, 10, 15, and 20 μm diameters and density of water were released during 0.42 s of cough event. Results of the airflow pattern in the room and droplets’ dispersion, aspiration, and deposition in the receptor’s mannequin airway were presented and discussed. The simulation results showed that the thermal plume considerably influenced the airflow around the mannequins. That is, the total aspiration fraction of droplets with the thermal plume is much more than the case without the thermal plume. The total deposition of small droplets in the receptor’s mannequin airway increases by considering the influence of the thermal plume. Deposition of droplets in the vestibule, main airway and branches is higher than the other parts of the airway. However, the regional deposition of droplets in the vestibule is similar with and without the thermal plume.