Experimental study of the dispersion of cough-generated droplets from a person going up- or downstairs

Abstract

The dispersion of cough-generated droplets from a person going up- or downstairs was investigated through a laboratory experiment in a water tunnel. This experiment was carried out with a manikin mounted at inclination angles facing the incoming flow to mimic a person going up or down. Detailed velocity measurements and flow visualization were conducted in the water tunnel experiments. To investigate the influence of the initial position on the motion of particles, a virtual particle approach was adopted to simulate the dispersion of particles using the measured velocity field. Particle clustering, which is caused by the unsteadiness of the flow, was observed in both flow visualization and virtual particle simulation. For the case of going upstairs, particles are concentrated below the person’s shoulder and move downward with a short travel distance. For the case of going downstairs, particles dispersing over the person’s head advect over for a long distance. We also found that the motion of the particles is closely related to the initial position. According to the results in this study, suggestions for the prevention of respiratory infectious disease are made.

Numerical model for cough‐generated droplet dispersion on moving escalator with multiple passengers

“…For the descending case with 10 passengers (see Figures 6C,G), flow separates at the hip and reattaches at the head while the separated flow from the head flows backward. This is similar to the experimental result in Wang et al 21 For the descending escalator (CASE III and IV), in the spaces between passengers, upwash blowing is observed. As a result, the flow separates from the head and advects over the heads at the further back position.…”

“…At the boarding positions of the third and subsequent passengers, downwash toward the steps is observed in the spaces between passengers, and flow separations at the hip are no longer observed. The steps generate a stronger flow in the direction of travel of the escalator than the simple sloping floor used in experiments 20,21 . The flows separate at the tip of the steps, and the magnitude of recirculation (vorticity) decreases as the distance from the first passenger increases due to an augmented flow entrainment.…”

“…Also, only a single passenger was included for risk evaluation of infectious droplets and the interaction with other passengers was ignored in the previous studies. 20,21 In this paper, we investigate the effect of cough-generated droplets expelled from an infected person on other passengers riding the same escalator. A geometrically detailed escalator model is used with steps and handrails moving in ascending and descending directions.…”

“…This is very different from real escalator environments, where a complex flow field is generated by a dynamic combination of moving steps, moving handrails, and static side panels. Also, only a single passenger was included for risk evaluation of infectious droplets and the interaction with other passengers was ignored in the previous studies 20,21 …”

“…The result showed that droplets expelled from an infected person on a descending escalator could travel long distances at the height of the person's head, and a person following behind was at risk. Wang et al 21 studied the dispersion of cough‐generated droplets from a person going upwards or downwards with a laboratory experiment in a water tunnel, using mannequin models similar to the one used by Li et al 20 They used a virtual particle simulation based on the velocity data from the experiments performed to study the effect of the initial position on particle concentration. The result showed that unsteady fluctuations of the airflow could result in the clustering of droplets, in contrast to droplet dispersion in a steady flow field.…”