Aerodynamic Particle Resuspension due to Human and Model Foot Motions

Human foot motions such as walking and foot tapping detach the particulate matter on the floor and redistribute it, increasing the particle concentration in air. The objective of this paper is to experimentally investigate the mechanism of particle resuspension and redistribution due to human foot motion. In particular, generation and deformation of vortex produced by the foot motion and how they are affected by the shape of sole have been examined. The experiments were carried out by particle flow visualization and the Particle Image Velocimetry (PIV) measurements in air, and dye flow visualization in water. The flow visualizations with human foot tapping and stomping were also carried out in order to elucidate the particle resuspension in real situations. In a laboratory experiment, the foot was modeled either as an elongated plate or a foot wearing a slipper, moving normal to the ground downward or upward. To focus on the aerodynamic effect, the model foot was stopped immediately above the floor before contacting the floor. The results indicated that the particles were resuspended both in downward motion and in upward motion of the foot. The particle resuspension and redistribution were associated with the wall jet between the foot and floor and the vortex dynamics. With an elongated plate, three-dimensional vortex structure strongly affected the particle redistribution.