Trailing vortices of Rushton turbine: PIV measurements and CFD simulations with snapshots approach

Understanding fluid dynamic characteristics of trailing vortices behind impeller blades and the capability to computationally simulate these vortices is essential for reliable design and scale-up of stirred reactors. In this paper, trailing vortices behind the blades of a standard Rushton turbine were studied using particle image velocimetry (PIV). Angle resolved and angle averaged flow fields near the impeller blades were measured and the structure of trailing vortices was studied in detail. A computational snapshot approach of Ranade and Dommeti was extended and used to simulate flow generated by the Rushton turbine in baffled stirred vessels. The approach was implemented using the commercial CFD code, FLUENT (of Fluent Inc, USA). Two turbulence models, namely, standard k - ε model and renormalization group version (RNG) of k - ε model were used for simulating the flow in stirred vessels. Predicted results were compared with the angle resolved PIV measurements to examine whether the computational model captures the flow structures around impeller blades. Predicted results were also compared with the angle averaged PIV data. Predicted gross flow characteristics like pumping number were also compared with the present and previously published experimental data. The results and conclusions drawn from this study will have important implications for extending the applicability of CFD models for simulating flow near impeller blades.