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_/ 流体力学セミナー ２００５ No. １２
_/ （京大理学部 物理COE「物理学の多様性と普遍性の探究拠点」の談話会との共催）
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_/ 日 時 : ０５年 １１月 ２１日 (月) １５：００〜１６：３０
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_/ 場 所 : ！！注意： 場所がふだんとは異なります！！
_/ 京大理学部５号館 (物理学教室) 第２講義室
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_/ 講 師： Jeremie Bec 氏(Observatoire de la Cote d’Azur, France)
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_/ 題 目： Large suspensions of inertial particles in turbulent flows
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_/ 内 容 :
_/ During the last ten years important progress has been made
_/ on a turbulence-related issue: tools borrowed from high-energy and
_/ statistical physics have been used to explain how anomalous scaling
_/ arises in the dynamics of passive scalar advected by incompressible
_/ turbulent flow. Much more violent phenomena take place when the
_/ dynamics is dissipative: trajectories generally concentrate on
_/ dynamically evolving singular sets with fractal and multifractal
_/ properties.
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_/ An instance is the case of dust, droplets, bubbles or other small
_/ impurities advected by turbulent flow. Such particles generally have
_/ a finite size and a mass density different from the fluid. They cannot
_/ be modeled by simple tracers: inertia effects are present in their
_/ dynamics. In a turbulent flows, eddies are responsible act as small
_/ centrifuges and eject particles leading to their concentration in the
_/ low-vorticity regions of the flow. The statistical description of
_/ such ¥emph{preferential concentrations} remains largely an open
_/ question, with applications, for instance, in the growth of rain drops
_/ in subtropical clouds or in the formation of planetesimals in the
_/ early Solar system.
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_/ I will present some results obtained for very diluted suspensions
_/ where particle-to-particle hydrodynamical interactions and retroaction
_/ of the particles on the fluid are disregarded. After relaxation of
_/ transients, the phase-space density of particles becomes singular with
_/ non-trivial multiscaling properties. Multifractality in phase space
_/ implies also multiscaling of the spatial distribution of the mass of
_/ particles. Numerical simulations in homogeneous isotropic turbulent
_/ flows and with heavy particles, allow the accurate determination of
_/ the scaling exponents. I will finally discuss how taking into account
_/ multifractal distributions of particles can be crucial in determining
_/ their collision rates.
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_/ References
_/ * J.Bec, “Fractal clustering of inertial particles in random flows”,
_/ Phys. Fluids 15, L81 (2003). [nlin.CD/0306049]
_/ * J.Bec, “Multifractal concentrations of inertial particles in smooth
_/ random flows”, J.Fluid Mech. 528 255–277 (2005). [nlin.CD/0402024]
_/ * J. Bec, A.Celani, M.Cencini & S.Musacchio, “Clustering and collisions
_/ of heavy particles in random smooth flows”,
_/ Phys.Fluids 17, 073301 (2005). [nlin.CD/0407013]
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_/ なお、講師は京大理学部物理COE「物理学の多様性と普遍性の探究拠点」の
_/ 招聘研究者として、11/12から12/4まで京大 理学部 物理学教室 流体物理学
_/ 研究室に滞在します。
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世話人：大木谷 耕司(京大数研)、藤 定義(京大理)、松本 剛(京大理)、
山田 道夫(京大数研)
アドバイザー：小森 悟（京大工）、藤坂博一（京大情報学）、
船越 満明（京大情報学）、水島 二郎(同志社大工)、余田 成男（京大理）
連絡先：ohkitani@kurims.kyoto-u.ac.jp
メールリスト連絡先： semi-adm@kyoryu.scphys.kyoto-u.ac.jp

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