A Multiscale Approach for Modeling Bubbles Rising in Non-Newtonian Fluids

The present work reports a multiscale approach to describe the dynamics of a chain of bubbles rising in non-Newtonian fluids. By means of the particle image velocimetry (PIV) and the lattice Boltzmann (LB) simulation, a deep understanding of the complex flow pattern around a single bubble is gained at microscale. The interactions and coalescences between bubbles rising in non-Newtonian fluids are experimentally investigated by the PIV measurements, birefringence, and rheological characterization for both an isolated bubble and a chain of bubbles formed from a submerged orifice. Two aspects are identified as central to interactions and coalescence: the stress creation by the passage of bubbles and their relaxation due to the fluid’s memory. This competition between the creation and relaxation of stresses displays nonlinear complex dynamics. Along with the detailed knowledge around a single bubble, these fundamental mechanisms governing the bubbles’ collective behavior in a train of bubbles at mesoscale leads to cognitive modeling on the basis of behavioral rules. By simulating bubbles as adaptive agents with the surrounding fluid via averaged residual stresses, model predictions for consecutive coalescence between a great number of bubbles compare very satisfactorily with the experimental investigation at macroscale.