Towards understanding the influence of Human Movement on Aerosol Dispersion

Human movement strengthens aerosol transmission within indoor spaces and the exhaled flow from humans acts as a jet dispersing the expelled air in the near field. This experimental study investigates both these mechanisms using a moving cylinder with a horizontal jet that originates from the face of a translating cylinder. Under the principle of dynamic similarity, a cylinder that replicates the human form (at 1/10th scale) is fabricated with an internal orifice to eject horizontal jet flow at a Reynolds number equivalent to the average human expiration rate. The cylinder is translated across the transparent water tank at a constant speed which is dynamically equivalent to human walking speed. Initial measurements of colour dye ejection from the stationary cylinder noted the highly dispersive nature of the horizontal jet. However, the jet dynamics were completely overwhelmed by the movement of the cylinder. High velocity regions directed towards the cylinder in the downstream region were observed on both planes together with a strong pull towards the base of the cylinder. Additionally, we observed vortical regions that extended downstream, which potentially gives rise to barriers containing contaminants in a particular region. These findings imply that the aerosols expelled by a walking human could be transported relatively greater distances as they are trapped by the shear layers. However, the downwash could lead to a portion of the aerosol being dragged towards the floor mitigating risks to others.