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DTSTART:20170326T030000
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DTSTAMP:20260428T111143Z
UID:58d0f52b86cce461294976@ist.ac.at
DTSTART:20170329T150000
DTEND:20170329T160000
DESCRIPTION:Speaker: Alfredo Soldati\nhosted by Björn Hof\nAbstract: Turbu
 lent fluids and small particles or droplets or bubbles are common to a num
 ber of key processes in energy production\,\nproduct industry and environm
 ental phenomena. In modelling these processes\, the dispersed phase is usu
 ally assumed uniformly\ndistributed. Indeed\, it is not. Dispersed phases 
 can be focused by turbulence structures and can have a time-space distribu
 tion\nwhich barely resembles prediction of simplified averaged modelling.\
 nPreferential distribution controls the rate at which sedimentation and re
 -entrainment occur\, reaction rates in burners or reactors\nand can also d
 etermine raindrop formation and\, through plankton\, bubble and droplet dy
 namics\, the rate of oxygen-carbon\ndioxide exchange at the ocean-atmosphe
 re interface.\nIn this talk\, we will review a number of physical phenomen
 a in which particle segregation in turbulence is a crucial effect\ndescrib
 ing the physics by means of Direct Numerical Simulation of turbulence.\nWe
  will elucidate concepts and modeling ideas derived from a systematic nume
 rical study of the turbulent flow field coupled\nwith Lagrangian tracking 
 of particles under different modeling assumptions. We will underline the p
 resence of the strong shear\nwhich flavors wall turbulence with a unique m
 ultiscale aspect and adds intricacy to the role of inertia\, gravity and b
 uoyancy in\ninfluencing particle motion. We will describe the role of free
  surface turbulence in dispersing and clustering the light particles\nsuch
  as plancton and the role of the distribution of dissipation in non-homoge
 neous turbulence to control breakage rates of brittle\nand ductile aggrega
 tes.\nThrough a number of physical examples of practical interest such as 
 boundary layers\, free-surface and stratified flows\, we\nwill show that a
  sound rendering of turbulence mechanisms is required to produce a physica
 l understanding of particle trapping\,\nsegregation and ultimately macrosc
 opic flows such as surfacing\, settling and re-entrainment.\n\nFigure 1. L
 ight particles floating on a flat shear-free surface of a turbulent open w
 ater. This configuration mimics the motion of buoyant matter\n(e.g. phytop
 lankton\, pollutants or nutrients). Correlation between floater clusters a
 nd surface divergence Ñ2D. Floaters segregatein Ñ2D < 0\nregions (in blu
 e\, footprint of sub-surface downwelings) avoiding footprint of sub-surfac
 e upwelings). Particle buoyancy induces clusters that\nevolve towards a lo
 ng-term fractal distribution in a time much longer than the Lagrangian int
 egral fluid time scale\, indicating that such clusters\nover-live the surf
 ace turbulent structures which produced them?.\nREFERENCES\nLovecchio\, S.
 \, Zonta\, F. and Soldati\, A.\, 2015 ”Upscale energy transfer and flow t
 opology in free surface turbulence\,” Phys.\nRev. E\, Vol. 91 033010.\nMa
 rchioli\, C. and Soldati\, A.\, 2015 ”Turbulent breakage of ductile aggre
 gates”\, Phys. Rev. E\, Vol. 91 053003.\nLovecchio\, S.\, Marchioli\, C.\
 , and Soldati\, A. 2013 ”Time persistence of floating particle clusters i
 n free-surface turbulence\,”\nPhys. Rev. E\, Vol. 88 033003.\nMarchioli\,
  C.\, and Soldati\, A.\, 2002 ”Mechanisms for Particle Transfer and Segre
 gation in Turbulent Boundary Layer”\, J.\nFluid Mech.\, Vol. 468\, pp. 28
 3-315.\nG.A. Voth\, A. Soldati 2017 ”Anisotropic particles in turbulence
 ”\, Annu. Rev. Fluid Mech.\, 49\, 249-276.
LOCATION:Seminar Room\, Lab Building East\, ISTA
ORGANIZER:rsix@ist.ac.at
SUMMARY:Alfredo Soldati: Physics and computations of turbulent dispersed fl
 ows: Macro- Consequences from Micro
URL:https://talks-calendar.ista.ac.at/events/570
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