LAUSR

Infectious respiratory diseases spread via droplets emitted by infected individuals. It is known that the emitted droplets vary from person to person because of geometrical differences. This study aimed to elucidate the influence of airway geometry on droplet generation and the maximum number of generations that should be considered when performing numerical analyses. As models for airway geometry, we chose the symmetric Weibel model and asymmetric Kitaoka model generated by a deterministic algorithm to compare the geometrical characteristics under the same volume, surface area, and other set parameters. The Kitaoka model showed a region of locally high air velocity, which was not observed in the Weibel model. Correspondingly, there were regions with localized high wall shear stress (WSS) values and large detached masses only in the Kitaoka model. Moreover, the locations of these localized regions differed depending on the maximum number of airway generations. Regarding the number of droplets generated, both models generated the same number of droplets of several to several tens of micrometers; however, the Kitaoka model generated more nanoscale-size droplets and large droplets of about 100 μm. This was explained by the WSS distribution and thickness of the airway wall mucosa. The thickness of the airway wall mucosa was attributed to the WSS, suggesting that the asymmetric geometry, which influences cough airflow, is an important indicator of droplet generation.