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Soutenance de thèse de Robin Guichardaz

Shape dynamics and clustering processes of particles transported by turbulent flows: a stochastic approach
When Oct 13, 2016
from 02:00 to 05:45
Where Amphithéâtre A (Site Monod)
Contact Name Robin Guichardaz
Attendees Robin Guichardaz
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This thesis deals with the dynamics of particles in turbulent flows and the formation of structures. Two physical situations are studied. First, we consider the dynamics of tracers, that is fluid particles having the same properties than that of the fluid, transported by a turbulent velocity field. A triplet of such particles forms a triangle, which tends to be flattened under the action of the incompressible flow. Second, inertial particles of density higher than that of the fluid and subjected to a viscous drag force usually cluster on regions of high density, leading to the formation of strange attractors. The approach followed in this thesis consists in modeling the action of the turbulent flow using tools of stochastic dynamics (such as Langevin equations), which allow us to obtain a effective description of these phenomena. For inertial particles, the attractors are characterized by a non-integer fractal dimension. The addition of an external noise in the equations of motion leads to a generalization of this notion to negative values, intrinsic to the dynamics in the absence of noise. This thesis shows that it is possible to formulate the two problems in terms of very general stochastic processes, whose prototype is the one describing the sedimentation of particles in the presence of a thermal noise. The determination of the characteristics of the solution requires a new approach. The solution proposed here is based on the large deviation theory.