Bending dynamics of semi-flexible particles in turbulent flows
Orateur : Dario Vincenzi
Laboratoire J.A. Dieudonné
Résumé : The study of hydrodynamic turbulence and turbulent transport has received considerable impulse from the development of Lagrangian techniques. The translational dynamics of tracer particles is indeed intimately related to the mixing properties of turbulent flows. Over the last fifteen years, attention has extended to the dynamics of particles possessing additional degrees of freedom, namely the extensional dynamics of elastic polymers and the alignment and the rotation of non-spherical particles. I will describe the Lagrangian statistics of yet another degree of freedom, i.e., I will consider semi-flexible particles that can bend under the action of a non-uniform flow. A semi-flexible particle will be modelled as a “trumbbell”, which consists of three beads connected by two rigid links and an elastic hinge at the middle. This simple model allows an analytical study of its dynamics. To gain intuition, I will first show that the dynamics of a trumbbell in a planar extensional flow is characterised by aperiodic end-to-end tumbling. I will then show that, in isotropic turbulence, the steady-state configuration depends strongly on the dimension of the flow. In 2D, the distribution of the bending angle is bimodal ; the folded and extended configurations are most probable, with the former configuration being the most likely for very strong turbulence. By contrast, in 3D, the extended configuration dominates and becomes increasingly probable as the amplitude of the velocity gradient increases. Such a sensitivity of the bending statistics on the dimensionality of the flow is peculiar to fluctuating flows and is not observed in laminar stretching flows.
Date et lieu : le Vendredi 16 Octobre 2015 à 11h00, salle de séminaire IRPHE