Date of Award
Doctor of Philosophy (PhD)
Philip Eric Wood
Characterization of the Rushton turbine (RT) and pitched blade turbine (PBT) impellers was undertaken with two objectives: (1) development of impeller boundary conditions which can be generally applied to CFD simulations of stirred tank flows for predictive purposes, and (2) accurate characterization of the turbulence quantities k and ε for use in model development and verification. Since the flow field for the RT is well characterized in the literature, work on this impeller proceeded directly to a fundamental model of the discharge flow. Using this swirling radial jet (SRJ) model, it was possible to accurately predict the impeller boundary condition, including k and ε. The predicted boundary condition was used in a three dimensional CFD simulation of the entire flow field. The results of this simulation accurately reproduce mean velocity profiles, the decay of k and ε in the bulk of the tank, and details of the flow behind the baffles. Characterization of the PBT commenced with mean velocity and flow visualization studies of the impeller discharge zone for various geometries. It was found that there is a definite transition of the entire time averaged flow field from a single circulation loop, to two circulation loops, which occurs at a specific off bottom clearance. It was also shown that the boundary condition is affected by feedback from this transition in the flow field. The time varying characteristics of the flow field were examined in some detail. Various proposed methods of estimating ε were applied, and the results compared. It was found that autocorrelation function methods revealed useful physical information about the flow, particularly the existence of not only the dominant blade passage frequency (BPF), but also a second, low frequency component in the flow. The effects of these frequencies on the calculated value of ε were examined. It has been possible to characterize the boundary conditions for both the RT and the PBT impellers, using both theoretical and experimental methods; and to show that mathematical modelling and CFD simulations based on the k-ε model can yield accurate and useful information about the flow field.
Kresta, Suzanne Marie, "Characterization, measurement and prediction of the turbulent flow in stirred tanks" (1991). Open Access Dissertations and Theses. Paper 3754.