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Soutenance de thèse ECL

Juan Ignacio Polanco

Vendredi 22 mars 2019 à 10h, ECL amphi 203, Bâtiment W1

Juan Ignacio Polanco

Lagrangian properties of turbulent channel flow : a numerical study

The Lagrangian perspective, describing a flow from the trajectories of fluid tracers, is a natural framework for studying dispersion phenomena in turbulent flows. In wall-bounded turbulence, the motion of fluid tracers is affected by mean shear and by strong inhomogeneity and anisotropy near walls.

We investigate the Lagrangian properties of a turbulent channel flow using direct numerical simulations at a moderate Reynolds number. Lagrangian acceleration statistics are compared to particle tracking experiments performed in parallel to this work. As in homogeneous isotropic turbulence (HIT), the acceleration components along Lagrangian paths decorrelate over time scales representative of the smallest scales of the flow, while the acceleration norm stays correlated for much longer. The persistence of small-scale anisotropy far from the wall is demonstrated in the form of a non-zero cross-correlation between acceleration components.

The dispersion of tracers in the channel is then considered. As a result of the average fluxes of kinetic energy in wall turbulence, tracers initially located close to the wall travel and spread over longer distances when tracked backwards in time than forwards. The relative dispersion of tracer pairs is finally investigated. At short times, pair separation is ballistic for all wall distances. As in HIT, relative dispersion is time asymmetric, with tracers separating faster when tracked backwards in time. At longer times, mean shear dominates leading to rapid separation in the mean flow direction. A ballistic cascade model previously proposed for HIT is adapted to inhomogeneous flows.

Jury :

Jérémie BEC — MINES ParisTech, CEMEF, Sophia-Antipolis (rapporteur)
François SCHMITT — LOG, Université de Lille (rapporteur)
Micheline ABBAS — LGC, INP Toulouse
Jean-Philippe MATAS — LMFA, Université Lyon 1
Nicolas MORDANT — LEGI, Université Grenoble Alpes
Ivana VINKOVIC — LMFA, Université Lyon 1 (directrice de thèse)
Mickaël BOURGOIN — Laboratoire de Physique, ENS de Lyon (invité)


  • Vendredi 22 mars 10:00-11:00 -

    thèse : Juan Ignacio Polanco

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