Persistent accelerations disentangle Lagrangian turbulence

Abstract

Particles in turbulence frequently encounter extreme accelerations between extended periods of quiescence. The occurrence of extreme events is closely related to the intermittent spatial distribution of intense flow structures such as vorticity filaments. This mixed history of flow conditions leads to very complex particle statistics with a pronounced scale dependence, which presents one of the major challenges on the way to a non-equilibrium statistical mechanics of turbulence. Here, we introduce the notion of persistent Lagrangian acceleration, quantified by the squared particle acceleration coarse-grained over a viscous time scale. Conditioning Lagrangian particle data from simulations on this coarse-grained acceleration, we find remarkably simple, close-to-Gaussian statistics for a range of Reynolds numbers. This opens the possibility to decompose the complex particle statistics into much simpler sub-ensembles. Based on this observation, we develop a comprehensive theoretical framework for Lagrangian single-particle statistics that captures the acceleration, velocity increments as well as single-particle dispersion.

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• An Efficient Particle Tracking Algorithm for Large-Scale Parallel Pseudo-Spectral Simulations of Turbulence
• On small-scale and large-scale intermittency of Lagrangian statistics in canopy flow
• Lagrangian Irreversibility and Eulerian Dissipation in Fully-Developed Turbulence
• Flow of Spatiotemporal Turbulentlike Random Fields
• Dynamics of finite-size spheroids in turbulent flow: the roles of flow structures and particle boundary layers
• 3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field
• Shear and bulk acceleration viscosities in simple fluids
• Temporal large-scale intermittency and its impact on the statistics of turbulence
• Multi-time structure functions and the Lagrangian scaling of turbulence