Roberto Zenit and James J. Feng
Ann. Rev. Fluid Mech. 50 (to appear in January 2018).
Abstract - The understanding of hydrodynamic forces around particles, drops or bubbles moving in Newtonian liquids is modestly mature. It is possible to obtain predictions of the attractive-repulsive interaction for moving ensembles of dispersed particulate objects. There is a certain intuition of what the effects of viscous, inertial and surface tension forces should be. When the liquid is non-Newtonian the intuition is gone. In this review we summarize recent efforts to gain fundamental understanding of hydrodynamic interactions in non-Newtonian liquids. Due to the complexity of the problem, most investigations rely on experimental observations. However, computations of non-Newtonian fluid flow have made increasingly significant contributions to our understanding of particle, drop and bubble interactions. We focus the review on gravity driven flows: rise or sedimentation of single spheroidal objects, pairs and dispersions. We identify the effects of two main rheological attributes — viscoelasticity and shear-dependent viscosity — on the interaction and potential aggregation of particles, drops and bubbles. We end by highlighting the open questions on the subject, and suggesting future directions of investigation toward the fundamental physics as well as applications.