Tue June 11th 2019
16:00 – 17:00
Seminar Dust, snowflakes, and other stories
Filippo Coletti


Multiphase flows in which an inertial dispersed phase interacts with a carrier fluid are ubiquitous in environmental, industrial and biomedical settings: from atmospheric precipitation, to combustion, to drug delivery. Even stripped down to its minimal components, the problem remains complex because of the wide range of scales involved and the multiple physical parameters at play. In this talk, I will first focus on the seemingly simple case of dilute microscopic particles falling through homogeneous air turbulence. A unique experimental facility is leveraged, in which hundreds of jets are individually and automatically controlled to produce the largest volume of zero-mean-flow homogeneous turbulence ever created. Using high-resolution laser imaging, I will show how inertial particles cluster in specific regions of the flow, leading to a multi-fold increase in fall speed compared to their terminal velocity in quiescent air. Heavier particles instead display surprisingly large accelerations as they fall through turbulence. The relevance of such observations and their correct scaling is demonstrated by outdoor field measurements, in which snowflakes are tracked in the atmosphere using high-speed cameras, displaying similar behaviors as the laboratory experiments. These results are being incorporated in weather forecasting models, leading to improved predictions of snow accumulation.


Filippo Coletti is the McKnight Land-Grant Professor of Aerospace Engineering & Mechanics and member of the St. Anthony Falls Laboratory at the University of Minnesota, where he has been since 2014. Previously he was postdoctoral fellow at Stanford University, and performed his doctoral studies at the von Karman Institute (Belgium) and at the University of Stuttgart (Germany) where he obtained his PhD in 2010. He is the recipient of the NSF CAREER Award, the 3M Non-Tenured Faculty Award, and the McKnight Land-Grant Professorship. His interests revolve around the transport of particles in vortical and turbulent flows, leveraging a wide spectrum of experimental approaches and with applications to both biomedical and environmental problems. His research is funded by the National Science Foundation, the National Institute of Health, the Army Research Office, the Office of Naval Research, the State of Minnesota, and industry partners.
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The 10th Complex Motion in Fluids 2021
Max Planck Gesellschaft
Centre for Scientific Computing