This Special Issue is a second collection of top-quality papers from some of the Editorial Board Members of Fluids, Guest Editors, and leading researchers, discussing new knowledge or new cutting-edge developments in all aspects of fluid mechanics. Research in turbulence continues to be one of the active areas; other papers focus on mixing, multiphase flows and porous media, slow (creeping) flows, potential flows, non-Newtonian fluids, fluid-structure interaction, and numerical methods.