Abstract:

From marine litter to ice floes, natural bodies of water are often populated with floating objects that span vast ranges of size, shape and concentration. Predicting their behaviour requires understanding how the turbulent water motion is altered by the presence of the free surface, and how the underlying turbulence influences the interfacial dynamics between the surface and the floating objects, and between interacting floaters. Even in the seemingly simple case in which surface waves are negligible, the problem is rich of fascinating phenomena. I will present a series of experiments conducted in flow facilities large and small, in which marginally buoyant particles (millimetric to centimetric, round and not, solid and not) float on turbulent water. For simplicity, the main focus is kept on two opposite limits. First, I will consider dilute, non-interacting discs significantly larger than the dissipative scales of the turbulence. These exhibit translational and rotational motions dictated by the local flow, coarse-grained at the scale of the particle. Then, I will consider dense suspensions of smaller spherical particles. Those form multi-scale percolating clusters bound by capillarity, whose dynamics is well described by the population-balance framework. Finally, I will give hints of the profoundly different behaviour exhibited by floating rods and oil droplets.

Introduction of speaker:

Filippo Coletti is Professor of Experimental Fluid Dynamics at ETH Zurich, where he has been since 2020. Previously he was McKnight Land-Grant Professor of Aerospace Engineering & Mechanics at the University of Minnesota, which he joined in 2014. He performed his doctoral studies at the von Karman Institute for Fluid Dynamics and at the University of Stuttgart, where he obtained his PhD in 2010, and was postdoctoral fellow at Stanford University between 2011 and 2013. He received the CAREER award in 2015 from the US National Science Foundation and Consolidator grant in 2022 from the European Research Council. He is a fellow of the American Physical Society and associate editor of Journal of Fluid Mechanics. He founded and co-organizes the Fluid Mechanics Tour of the Alps, an itinerant seminar series featuring the world’s top fluid mechanicians. His research interests focus on multiphase flows, which he studies with a range of experimental approaches and with applications to environmental, biomedical, and industrial problems.

审核：刘有晟、游小清