The recirculating flow structures formed in the wake of a worker standing in front of an enclosing fume hood were numerically investigated. Two- and three-dimensional, unsteady, laminar/turbulent computations were performed for a Reynolds number (Re) range of 1.0 x 10(3)-1.0 x 10(5). The standard k-epsilon, Renormalization group (RNG) k-epsilon, and Shear Stress Transport (SST) k-omega models were used in Unsteady Reynolds Averaged Navier-Stokes (URANS) computations, and the results were compared with each other and also with the previous predictions reported in the literature. Numerical issues regarding the grid convergence and the inadequacies of turbulence models that may come into play at low Reynolds numbers were addressed. On the whole, SST k-omega model was found to be promising for qualitatively accurate prediction of both steady and unsteady recirculatory flow patterns in the wake of the worker. On the other hand, the standard and RNG k-epsilon models failed in prediction of anticipated unsteadiness at low Reynolds numbers. In a more realistic three-dimensional simulation with SST k-omega model, the anticipated unsteady and recirculating flow field in the wake of the worker was captured. Present results seem to qualitatively agree with the deductions made from experimental analyses in the literature while conflicting with some aspects of the previously reported numerical results. The apparent inconsistencies observed between the current results and those published in the literature were elucidated.
The present study concerns the flow dynamics and associated contaminant transport in the near wake of a worker using an industrial-type benchtop enclosing hood. The primary focus is on evaluating the effects on the dynamics of the wake flow and the exposure level of various extraneous factors, such as the strength and direction of cross-drafts and the worker's body heat and shape. Three-dimensional Unsteady Reynolds-Averaged Navier-Stokes simulations were carried out for a model of a simple mannequin and a model of an anthropometric mannequin. Estimated flow patterns and concentrations near the simple mannequin were compared with the observations from concurrent smoke visualization experiments and with the experimental concentration measurements, respectively. Results for both visualizations indicated that the flow in front of the worker is dominated by dynamic vortical structures and that body heat may have negative effects on the exposure level, especially at low flow rates. Using simple rounded shapes to simulate the human form was a fair approximation from the viewpoint of flow structures and exposure trends, which agreed well with the experimental measurements and observations. However, the quantitative values of the predicted concentrations in the breathing zone were sensitive to the mesh resolution.
New formalisms are developed for robust calculation of the discretization errors in CFD applications. The new methods are based on the premise that the true error (i.e. the difference between the exact solution and the numerical solution) on a given mesh is similar to the approximate error (i.e. the difference between the fine grid solution and the coarse grid solution). The proportionality constant can be calculated theoretically for a given scheme and it is, to a first order approximation, only a function of the grid refinement ratio. This method is called Approximate Error Scaling (AES) method.
Although AES is a viable method for error estimation it does not directly take into account the transport of error nor the error sources at the boundaries. To remedy this, a new method which is referred to, here and after, as the residual source in transport (REST-IC) method is formulated. This paper presents the theoretical details and the results from several test cases that are used for validation of the newly proposed methods.
Application to the 1D and 2D steady scalar transport equation and 2D Navier-Stokes (N-S) equations has revealed excellent performance with a pressure based segregated N-S finite volume solver. Implementation of these methods into CFD commercial codes such as ANSYS-FLUENT can be done with the help of expert developers of the code who can handle residuals for the selected equation and the variable through user defined subroutines.
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