Airflow around a child-size manikin in a low-speed wind environment

This work provides an understanding of how airflow patterns around humans can affect the concentrations and particle size distributions of particulate matter (PM) in the breathing zone. The focus of the experiments reported here is the flow around a child-size manikin under various conditions, including changes in body heat, breathing, wind speed, and body orientation relative to the wind direction. The airflow patterns that develop were investigated using laser Doppler anemometry. The presence of body heat changes the flow pattern most dramatically. With the manikin at room temperature, the flow pattern on the downstream side of the manikin consists of two slowly recirculating eddies. With the addition of body heat to the manikin, the flow pattern downstream of the manikin changes to a rising vertical plume with velocities on the order of 0.1 m/s. This vertical plume is capable of transporting PM into the breathing zone from near the floor. Increased wind speed decreases the relative importance of buoyancy. As the wind speed increases from 0.1 to 0.3 m/s, the vertical plume on the downstream side of the manikin is replaced by two recirculating eddies, a flow pattern similar to that with the unheated manikin. Changes in the relative importance of body heat and free-stream wind speed are quantified using a type of Richardson number.