Document Type

Article

Publication Date

11-18-2011

Publication Title

Physical Review Letters

Volume

107

First Page

214501

DOI

doi:10.1103/PhysRevLett.107.214501

Abstract

The mixing properties of turbulent flows are, at first order, related to the dynamics of separation of particle pairs. Scaling laws for the evolution in time of the mean distance between particle pairs (t) have been proposed since the pioneering work of Richardson.We analyze amodel which shares some featureswith 3D experimental and numerical turbulence, and suggest that pure scaling laws are only subdominant. The dynamics is dominated by a very wide distribution of ‘‘delay times’’ t_d, the duration for which particle pairs remain together before their separation increases significantly. The delay time distribution is exponential for small separations and evolves towards a flat distribution at large separations. The observed (t) behavior is best understood as an average over separations that individually follow the Richardson-Obukhov scaling, r^2 propto t^3, but each only after a fluctuating time delay t_d,where t_d is distributed uniformly.

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