PREDICTION OF THE 3-DIMENSIONAL TURBULENT-FLOW IN STIRRED TANKS

Efforts to model the turbulent flow in stirred tanks require accurate boundary conditions at the tip of the impeller, not just of velocities, but of the turbulence quantities kappa and epsilon. Kolar's (1982) phenomenological, swirling radial jet model of the impeller region is extended by using a two-equation kappa-epsilon turbulence model to obtain direct estimates of kappa and epsilon on the impeller periphery. The model is extended and clarified, so that the number of parameters required for its application is reduced to two: the rotational speed and the diameter of the impeller. Three-dimensional simulations allow a realistic treatment of the baffles. Agreement of the modeling results with recently published experimental data is excellent. This is particularly true in the important impeller discharge zone, where details of the predicted behavior of the turbulence kinetic energy and dissipation rate are in quantitative agreement with the available data. Based on these results, average values of epsilon are calculated, along with the zones over which they apply. For the impeller discharge zone, the dimensionless, volume-averaged epsilon is 0.19.