진학프로석·박사 채용 접수 플랫폼

The turbulent dynamics of macroscopic fibers involves a complex interplay between translation and deformation across multiple spatial and temporal scales. Its study presents a significant challenge compared to microscopic objects, whose deformation is primarily influenced by velocity gradients. Understanding the behavior of macroscopic fibers in turbulence remains largely unexplored, despite its critical implications for natural systems (planktonic colonies), industrial processes (papermaking), and environmental concerns (plastic debris in the oceans). Previous research on fiber dynamics in turbulence has primarily focused on isolated objects, examining tumbling and spinning motions, statistical properties of deformation, and interactions with coherent structures. Despite these efforts, fundamental questions regarding the dynamics of individual fibers remain unresolved, and there is a significant gap in our understanding of the collective behavior of fiber ensembles. This postdoctoral position is part of a larger project aimed at understanding and modeling the processes of fiber fragmentation and aggregation. The project leverages a multidisciplinary approach, combining mathematical modeling, numerical simulations, statistical physics, and laboratory experiments.

The objective is to study models for long, thin, flexible fibers, such as slender bodies or articulated chains, to accurately account for break-ups, knots, fiber-fiber interactions, and entanglement. These models will be used to understand how these processes are influenced by turbulent fluctuations, aiming to provide a comprehensive statistical representation in idealized flows, both with and without boundaries. Fragmentation – Vigorous turbulent strains can cause tensile, flexural, or torsional failures of filaments. The objective is to understand how these breakups depend on previously neglected aspects such as finite fiber length and mass, non-Markovian effects due to plasticity, and the time intermittency of the fluid flow. The aim is to explain universal distributions of fragments. Knots, Links, and Entanglement – In turbulent flows, fibers can assemble, tie up, and form dense balls. For longer fibers, flow nonlinearity or buckling can lead to the formation of knots. By considering the microscopic details of these processes, our objective is to investigate how turbulence influences, amplifies, or weakens the formation of aggregates and to develop effective models for their dynamics.

Proposed Methodology – The proposed method consists in employing simplified coarse-grained models of fibers, such as slender-body theory and bead-spring chains used in the kinetic theory of polymeric fluids. These models will be studied both theoretically and numerically in random flows and direct numerical simulations of Navier–Stokes equations using existing codes. The hired postdoc will participate to any of these aspects depending on his/her skills and preferences. The theoretical and numerical results will be validated through experimental collaborations with our project partners. Experiments will be conducted in a turbulent von-Kármán-like flow at IRPHE in Marseille and in a turbulent channel flow setup at INPHYNI in Nice. These experimental setups will provide critical data to corroborate our simulation outcomes and refine our models.

Host Laboratories – The hired postdoctoral fellow will be hosted at the mathematics department (Laboratoire J.-A. Dieudonné) or the physics department (Institut de Physique de Nice) of Université Côte d’Azur or both. The Laboratoire J.A. Dieudonné specializes in advanced research in pure and applied mathematics. The postdoc will join the “Numerical Modeling and Fluid Dynamics” team, interacting with experts in the numerical and theoretical modeling of turbulent transport. At the Institut de Physique de Nice, the postdoc will be part of the “Nonlinear and Out-of-Equilibrium Physics” team, which focuses on statistical physics, fundamental aspects of turbulence, turbulent transport, and large-scale direct numerical simulations of turbulent flows.