Anomalous dispersion of Lagrangian particles in local regions of turbulent flows revealed by convex hull analysis

TL;DR

This paper investigates local anomalous particle dispersion in turbulent flows using convex hull analysis, revealing instances of particle clustering and anisotropic effects across various turbulence types.

Contribution

It introduces convex hull analysis as a novel method to identify and analyze local anomalous dispersion events in different turbulent flow regimes.

Findings

Convex hulls generally grow in turbulent flows but occasionally shrink, indicating non-dispersive local behavior.

Shrinkage events are more frequent in flows with anisotropy, such as magnetic fields or thermal convection.

The method applies across multiple turbulence types, including MHD and Boussinesq convection.

Abstract

Local regions of anomalous particle dispersion, and intermittent events that occur in turbulent flows can greatly influence the global statistical description of the flow. These local behaviors can be identified and analyzed by comparing the growth of neighboring convex hulls of Lagrangian tracer particles. Although in our simulations of homogeneous turbulence the convex hulls generally grow in size, after the Lagrangian particles that define the convex hulls begin to disperse, our analysis reveals short periods when the convex hulls of the Lagrangian particles shrink, evidence that particles are not dispersing simply. Shrinkage can be associated with anisotropic flows, since it occurs most frequently in the presence of a mean magnetic field or thermal convection. We compare dispersion between a wide range of statistically homogeneous and stationary turbulent flows ranging from homogeneous isotropic Navier-Stokes turbulence over different configurations of magnetohydrodynamic turbulence and Boussinesq convection.