Critical issues for predicting worker exposure to gaseous contaminants in a wind tunnel

In this study, three dimensional computational fluid dynamics (CFD) simulations are used to investigate the distribution and level of contaminant concentrations in the breathing zone of a worker when airborne contaminants are released within an arm\u27s-length in front of the worker who has his back to the airflow. The main goals were to numerically evaluate the effect of different factors on the worker exposure and to recommend a turbulence model preferable for this type of simulation. These factors include the body shape, the heat flux from the body, the ventilation intensity, the free stream turbulence, and the unsteadiness. The comparison between the numerical results and the experimental data has shown good agreement.;An extensive case study with FLUENT concluded with the following observations: (1) The heat flux from the body significantly affects the flow field and the subsequent contaminant concentration field at low Reynolds numbers; (2) The free stream turbulence plays an important role in the variation of exposure measurements at low Reynolds numbers; (3) Results calculated with the Large Eddy Simulation (LES) illustrate the turbulence structure in the wake of the manikin and indicate that the flow unsteadiness plays an important role in the variation of exposure measurements; (4) Calculations with various body shapes suggests that oversimplified body shapes may lead to inaccurate predictions in worker exposure assessment; (5) The concentrations measured at the lapel could be very different than the concentrations measured near the mouth.;To further improve the predictability of turbulence models for the present study, a non-linear (cubic) low-Re turbulence model has been selected, modified and implemented in the DREAM code which was developed at West Virginia University. Benchmark tests on turbulent channel flow, backward facing step flow and flow around a square cylinder have shown that this model is remarkably superior to linear eddy-viscosity models, and the results are even comparable to others\u27 predictions with LES, which is much more computationally expensive. So it could be a good alternative as a reliable and accurate turbulence model in simulating turbulent flow past a bluff body