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.

中文翻译：

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自动扶梯坡度和速度对乘客咳嗽飞沫扩散的影响


在 COVID-19 大流行期间，鼓励公众走楼梯或自动扶梯，而不是乘坐电梯。然而，这些地方以斜坡和人体运动为特征的呼吸道飞沫的扩散尚不清楚。因此，目前尚不清楚普遍推荐的社交距离准则是否仍然适用于这些情况。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的扩散，重点研究了自动扶梯的坡度和速度对飞沫扩散的影响。在模拟中，采用单向耦合欧拉-拉格朗日方法，使用雷诺平均纳维-斯托克斯方法求解气流，并将液滴建模为被动拉格朗日粒子。研究发现，坡度显着改变了乘客尾流中液滴的垂直浓度。咳嗽产生的喷射流的偏转和乘客身后的尾流使咳嗽产生的飞沫在下降自动扶梯时向上驱动，在上升时向下驱动，导致下降的自动扶梯上的病毒飞沫比在自动扶梯上的悬浮高度更高，传播范围更大。一个上升的。这些发现表明，目前的社交距离准则对于下降自动扶梯可能不够充分，需要进一步调查。