Semester

Spring

Date of Graduation

2011

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Ismail Celik.

Abstract

Effective exhaust hoods are critical for protection of workers from airborne contaminants. The present study investigates the flow dynamics and associated contaminant dispersion in the near-wake of a worker working at a bench- top enclosing hood. The focus is primarily placed on evaluating the effects of different factors such as cross-draft, body heat and body shape on the dynamics of the wake flow and eventually on the exposure level. For this purpose, extensive two- and three-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations are carried out using the commercial Computational Fluid Dynamics (CFD) software, called FLUENT, with various turbulence models, such as SST k -- o, RNG k -- epsilon and Standard k -- epsilon. The predictions from two-dimensional cases suggest that the SST k -- o model is more responsive to unsteady flow dynamics. The RNG k -- epsilon and Standard k -- epsilon models, on the other hand, are found overly diffusive, and hence, are not as successful as SST k -- o model in capturing the unsteady phenomena.;Three-dimensional simulations indicate that the flow separation around the worker's body is, to a large extent, hindered by the acceleration of the flow under the effect of suction. Hence, the anticipated lateral recirculation zones expanding into the hood do not always form. However, dynamic large-scale helical motions are found to characterize the flow from the hood face to the back of the hood. The simulated flow patterns are compared with the observations from concurrent smoke visualization experiments and they seem to capture the observed average flow field well. The negative effect of body heat on the exposure level is more pronounced at low flow rates. Comparison of predictions using simple, round, and complex, anthropometrically-scaled manikins reveals that the simple, round body is an acceptable representation of the realistic body from the viewpoint of exposure level. The predicted exposure trends agree well with the experimental measurements. However, the quantitative values of the predicted concentrations are highly sensitive to the grid resolution.;In a further attempt to apply Large Eddy Simulation (LES) to such a dynamic problem, an in-house CFD code, called DREAM, has been made parallel using Domain Decomposition Technique and the predictions are validated against benchmark solutions available in the literature. Moreover, a strongly monotone Quasi-Second Order Upwind (QSOU) convection scheme is implemented for accurate solution of scalar transport along with a feedback forcing based Immersed Boundary (IB) method to account for solid bodies immersed in the fluid. The new code (DREAM P) is applied for LES of the original worker-hood problem. The results agree favorably with the URANS simulations. The DREAM_P forms a much simpler computational platform compared to FLUENT for further study of flows dominated by bluff bodies.

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