title: Velocity-gradient statistics along particle trajectories in turbulent flows: the refined similarity hypothesis in the Lagrangian frame.
abstract: We present an investigation of the statistics of velocity gradient related quantities, in particular energy dissipation rate and enstrophy, along the trajectories of fluid tracers and of heavy/light particles advected by a homogeneous and isotropic turbulent flow. The refined similarity hypothesis (RSH) proposed by Kolmogorov and Oboukhov in 1962 is rephrased in the Lagrangian context and then tested along the particle trajectories. The study is performed on state-of-the-art numerical data resulting from numerical simulations up to Re(lambda) approximately 400 with 2048(3) collocation points. When particles have small inertia, we show that the Lagrangian formulation of the RSH is well verified for time lags larger than the typical response time tau(p) of the particle. In contrast, in the large inertia limit when the particle response time approaches the integral time scale of the flow, particles behave nearly ballistic, and the Eulerian formulation of RSH holds in the inertial range.
authors.affiliation: International Collaboration for Turbulence Research and Department of Physics and INFN, University of Tor Vergata, Via della Ricerca Scientifica 1, Rome, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Benzi
authors.forename: Luca
authors.initials: L
authors.lastname: Biferale
authors.forename: Enrico
authors.initials: E
authors.lastname: Calzavarini
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse
authors.forename: Federico
authors.initials: F
authors.lastname: Toschi