Experiments and predictions of the transition of the flow pattern with impeller clearance in stirred tanks

In the present work, the double- to single-loop flow pattern transition in a stirred vessel equipped with a Rushton turbine is investigated by Laser Doppler anemometry (LDA). In particular, the clearance at which such transition occurs is assessed by comparing axial velocity profiles underneath the impeller. Computational fluid dynamics (CFD) simulations of the same system are carried out, by employing the 'inner-outer' fully predictive computation strategy. The comparison of predicted results with the experimental data collected shows that the transition is well reproduced by simulations. A good agreement on the mean velocities is also observed but for the impeller discharge stream angle to the horizontal in the single-loop flow pattern configuration. Finally the predicted turbulent fluctuations are underestimated, a finding in agreement with those of most earlier CFD predictions. © 2001 Elsevier Science Ltd.