<p>This Special Issue is a second collection of top-quality papers from some of the Editorial Board Members of <em>Fluids</em> 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.</p>