Control of exposure caused by a contaminant source in the near wake region

A person in a unidirectional air flow may be exposed to considerable amounts of airborne contaminants if the contaminant source is within the wake region downstream of the body. This study examined how a local vertical air supply and a local exhaust can reduce the transport of contaminants from the near wake region to a mannequin's breathing zone in a unidirectional air flow. This transportation was studied by releasing a tracer gas from several points within the wake region, one point at a time, and measuring the breathing zone concentration with different local air supply and exhaust flow rates. Numerical simulations were also done in the case of a local air supply using the standard k-e model for turbulence closure. By focusing the control measures on the wake region, improved contaminant control with relatively small air flow rates can be achieved. Although both ventilation methods studied reduced the breathing zone concentration, the arrangement that involved the use of the local air supply was more efficient than the local exhaust method in controlling the exposure. The relative changes in the mean exposure could be satisfactorily predicted with numerical simulations and a particle tracking method.