Interactions of exhaled buoyant jet flow and human motion-induced airflow: An experiment study in a water tank

Abstract

Indoor environments with displacement ventilation or under-floor air distribution commonly exhibit thermal stratification, which can impact the dispersion of droplets in exhaled air by moving human sources. This paper presented an experimental study using a water tank to simulate the coupling characteristics of exhaled airflow and human motion-induced oncoming airflow, especially in a stratified environment. The effects of exhalation velocity and movement speed were studied. Results show that the buoyant jet flow couples with the oncoming flow, firstly spreading forwards and upwards, forming the impinging region, where the penetration distance is found to vary linearly with the ratio of movement velocity and exhalation velocity. Then the coupled flow spreads backwards, forming the wake region behind the source, where the flow rises upwards, albeit at a slower rate than in motionless conditions. In the wake region, there is an obvious stagnant layer, which is exacerbated by the thermal stratification of the ambient fluid and much lower than the lock-up height of motionless buoyant jet flow. It is expected to provide scientific basis for formulating prevention and control measures in public spaces.