Two-Equation Turbulence Modeling for Impeller Stirred Tanks

In this study, the predictive performance of six different two-equation turbulence models on the flow in an unbaffled stirred tank has been investigated. These models include the low Reynolds number $k-ε$ model of Rodi, W., and Mansour, N. N., “Low Reynolds Number $k-ε$ Modeling With the Aid of Direct Simulation Data,” J. Fluid Mech., Vol. 250, pp. 509–529, the high and low Reynolds number $k-ω$ models of Wilson, D. C., 1993, Turbulence Modeling for CFD, DCW Industries, La Canada, CA., the RNG $k-ε$ model, and modified $k-ω$ and $k-ε$ models which incorporate a correction for streamline curvature and swirl. Model results are compared with experimental laser Doppler velocimetry (LDV) data for the turbulent velocity field in an unbaffled tank with a single paddle impeller. An overall qualitative agreement has been found between the experimental and numerical results with poor predictions observed in some parts of the tank. Discrepancies in model predictions are observed in the anisotropic regions of the flow such as near the impeller shaft and in the impeller discharge region where the model overpredicts the radial velocity component. These results are discussed and a strategy for improving two-equation models for application to impeller stirred tanks is proposed.