Bubble trapping in a stirred vessel

We study a highly unexpected focusing phenomenon encountered in high-viscosity stirred fluids. In this project, we aim to uncover the fundamental focusing mechanism theoretically and experimentally. A fully three-dimensional direct numerical simulation is performed where the interface solver is based on a hybrid Front Tracking/Level Set method and designed to handle highly deforming interfaces with complex topology changes including pinch-off and coalescence. The form of the six-bladed Rushton turbine is constructed by means of a module for the definition of immersed objects via a distance function that takes into account the object’s interaction with the flow and treated as a fictitious fluid in the Navier-Stokes solution and its velocity is corrected in order to satisfy rigid body motion constraint. Bubbles are introduced into the system at various locations, and we demonstrate the conditions under which the motion of the bubbles is focused near the turbine impeller. The mechanisms underlying the bubble ‘trapping’ are also elucidated