Predicting breathing zone concentrations of aerosols dispersed in a time dependent airflow using vortex methods.

When a person works facing a local exhaust ventilation (LEV) hood, it may be possible to obtain higher concentrations of aerosols in the breathing zone (BZ) than without the hood because recirculating eddies form downstream of the body. These eddies shed periodically in an alternating pattern called vortex shedding, which is thought to be a primary determinant of contaminant transport in and out of the breathing zone (1, 2, 3). Previous computational fluid dynamics (CFD) studies have explored the effect of timedependent airflow on occupational exposure to gaseous contaminants (2, 3). However, none have employed CFD to assess occupational exposure to aerosols in a periodic air stream. In the present study, a two-dimensional Discrete Vortex Method (DVM) is used in conjunction with a Lagrangian particle-tracking algorithm to model this situation; particle number concentrations are then computed over a computational breathing zone.