Mixing dynamics in an uncovered unbaffled stirred tank using Large-Eddy Simulations and a passive scalar transport equation

Abstract

In this study, several large eddy simulations were performed to solve the free-surface flow in an uncovered unbaffled stirred tank driven by a Rushton turbine using different Froude numbers and impeller clearance settings. The numerical code developed is based on the pseudo-compressibility method. To solve the flow equations and track the free surface, compact finite difference schemes and the level set method were used. For the treatment of the boundary conditions at the interface and for the tank internals representation, the ghost fluid method was used. The liquid surface was studied and showed excellent agreement when compared with previous experimental studies. The trailing vortices behind the impeller blades were visualized. Additionally, other important turbulent structures were captured moving over the impeller and around the critical radius. Finally, a passive scalar equation was added to show part of the mixing dynamics, in which an important segregated zone appeared under the impeller.