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SUMMARY:Particles and swowflakes falling through turbulence
DTSTART:20210211T121500
DTEND:20210211T131500
DTSTAMP:20261002T022258Z
UID:15c05590650eb7378875b885a67a967b6f18a4db18d43908665cf54a
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Dr. Filippo COLETTI of ETH Zurich\nAbstract: Multiphase
  flows in which an inertial dispersed phase interacts with a turbulent flu
 id flow are ubiquitous in environmental\, industrial and biomedical settin
 gs. Even stripped down to its minimal components\, the problem remains com
 plex because of the wide range of scales involved and the multiple physica
 l parameters at play. In this talk\, I will first focus on the seemingly s
 imple case of dilute microscopic spherical particles falling through homog
 eneous air turbulence. A unique experimental facility is leveraged\, in wh
 ich hundreds of jets are individually controlled to produce the largest vo
 lume of zero-mean-flow homogeneous turbulence ever created. Using high-res
 olution laser imaging\, I will show how inertial particles group in larger
  clusters than previously thought\, experiencing anomalously large acceler
 ations and a multi-fold increase in fall speed compared to their still-air
  terminal velocity. At concentrations found in dust storms\, the particles
  also cause a substantial increase in turbulence intensity\, at odds with 
 most numerical simulations. The relevance of such observations is demonstr
 ated by outdoor field measurements\, in which snowflakes are illuminated a
 nd tracked over vertical planes about 30 m^2 using high-speed cameras. The
  snow particles display strikingly similar behaviors as seen in the labora
 tory\, including self-similar clustering\, anomalous accelerations\, and t
 urbulence-enhanced fall speed. These findings demonstrate that the fundame
 ntal phenomenology of particle-laden turbulence can be leveraged towards t
 he predictive understanding of snow precipitation. They also demonstrate h
 ow environmental flows can be used to investigate dispersed multiphase flo
 w physics at Reynolds numbers not accessible in laboratory experiments or 
 numerical simulations.\n 
LOCATION:https://ethz.zoom.us/j/94817809233?pwd=N0pzbnQwSFFTQnVPcVR3SkNrd2
 9OQT09
STATUS:CONFIRMED
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