Hydrodynamics in a stirred tank with a retreat blade impeller: Evaluating the potential of IBM-LES through comparison with PIV data

Abstract

This work presents numerical and experimental studies on the turbulent flow in a stirred tank reactor equipped with a two-finger baffle and a retreat blade impeller at Re = 43,200. Numerical results were obtained from Large Eddy Simulation (LES) combined with an Immersed Boundary Method (IBM) for the impeller and baffle representation. The experimental data consists in a set of PIV measurements in a vertical plane containing the shaft axis. The numerical results are compared with experimental data in terms of the flow field, mean velocity components, and kinetic energy. Proper Orthogonal Decomposition (POD) is applied to the IBM-LES results to extract the dominant modes and their time coefficients. The POD analysis suggests that the high energy level found in the upper part of the tank results from an energy transfer from the coherent structures created downstream the two-finger baffle. Finally, the trailing vortices behind the impeller blades and the baffle were detected and visualized using Jeong and Hussain's technique. The results show that IBM-LES is a reliable tool for studying the unsteady characteristics of turbulent flow in agitated tanks with complex geometry.