Li Zhaobin, Zhang Xinlei, Wu Ting, Zhu Lixing, Qin Jianhua, Yang Xiaolei
Phys Fluids (1994). 2021 Apr;33(4):041701. doi: 10.1063/5.0046870. Epub 2021 Apr 2.
During the pandemic of COVID-19, the public is encouraged to take stairs or escalators instead of elevators. However, the dispersion of respiratory droplets in these places, featured by slopes and human motion, is not well understood yet. It is consequently unclear whether the commonly recommended social-distancing guidelines are still appropriate in these scenarios. In this work, we analyze the dispersion of cough-generated droplets from a passenger riding an escalator with numerical simulations, focusing on the effects of the slope and speed of the escalator on the droplet dispersion. In the simulations, a one-way coupled Eulerian-Lagrangian approach is adopted, with the air-flow solved using the Reynolds-averaged Navier-Stokes method and the droplets modeled as passive Lagrangian particles. It is found that the slope alters the vertical concentration of the droplets in the passenger's wake significantly. The deflection of cough-generated jet and the wake flow behind the passenger drive the cough-generated droplets upwards when descending an escalator and downwards when ascending, resulting in both higher suspension height and larger spreading range of the viral droplets on a descending escalator than on an ascending one. These findings suggest that the present social-distancing guidelines may be inadequate on descending escalators and need further investigation.
在新冠疫情期间，鼓励公众走楼梯或乘自动扶梯而不是电梯。然而，对于这些场所中以坡度和人体运动为特征的呼吸道飞沫扩散情况，目前还了解得不够充分。因此，尚不清楚通常推荐的社交距离指导原则在这些场景中是否仍然适用。在这项工作中，我们通过数值模拟分析了乘坐自动扶梯的乘客咳嗽产生的飞沫扩散情况，重点关注自动扶梯的坡度和速度对飞沫扩散的影响。在模拟中，采用了单向耦合欧拉 - 拉格朗日方法，使用雷诺平均纳维 - 斯托克斯方法求解气流，将飞沫建模为被动拉格朗日粒子。研究发现，坡度会显著改变乘客尾流中飞沫的垂直浓度。咳嗽产生的射流偏折以及乘客身后的尾流，使得下行自动扶梯时咳嗽产生的飞沫向上运动，上行时向下运动，导致下行自动扶梯上病毒飞沫的悬浮高度更高、传播范围更大，相比上行自动扶梯而言。这些发现表明，目前的社交距离指导原则在下行自动扶梯上可能并不充分，需要进一步研究。
