title: Preferential Rotation of Chiral Dipoles in Isotropic Turbulence.
abstract: We introduce a new particle shape which shows preferential rotation in three dimensional homogeneous isotropic turbulence. We call these particles chiral dipoles because they consist of a rod with two helices of opposite handedness, one at each end. 3D printing is used to fabricate these particles with a length in the inertial range and their rotations are tracked in a turbulent flow between oscillating grids. High aspect ratio chiral dipoles preferentially align with their long axis along the extensional eigenvectors of the strain rate tensor, and the helical ends respond to the extensional strain rate with a mean spinning rate that is nonzero. We use Stokesian dynamics simulations of chiral dipoles in pure strain flow to quantify the dependence of spinning on particle shape. Based on the known response to pure strain, we build a model that gives the spinning rate of small chiral dipoles using velocity gradients along Lagrangian trajectories from high resolution direct numerical simulations. The statistics of chiral dipole spinning determined with this model show surprisingly good agreement with the measured spinning of much larger chiral dipoles in the experiments.
authors: Department of Physics, Wesleyan University, Middletown, Connecticut 06459, USA.
authors: Stefan
authors: S
authors: Kramel
authors: Department of Physics, Wesleyan University, Middletown, Connecticut 06459, USA.
authors: Greg A
authors: GA
authors: Voth
authors: Department of Applied Physics, Eindhoven University of Technology, 5600 MB, Eindhoven, Netherlands.
authors: Saskia
authors: S
authors: Tympel
authors: Department of Applied Physics and Department of Mathematics and Computer Science, Eindhoven University of Technology, 5600 MB, Eindhoven, Netherlands and Istituto per le Applicazioni del Calcolo, Consiglio Nazionale delle Ricerche, Via dei Taurini 19, 00185 Rome, Italy.
authors: Federico
authors: F
authors: Toschi