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

摘要

Local regions of anomalous particle dispersion, and intermittent events thatoccur in turbulent flows can greatly influence the global statisticaldescription of the flow. These local behaviors can be identified and analyzedby comparing the growth of neighboring convex hulls of Lagrangian tracerparticles. Although in our simulations of homogeneous turbulence the convexhulls generally grow in size, after the Lagrangian particles that define theconvex hulls begin to disperse, our analysis reveals short periods when theconvex hulls of the Lagrangian particles shrink, evidence that particles arenot dispersing simply. Shrinkage can be associated with anisotropic flows,since it occurs most frequently in the presence of a mean magnetic field orthermal convection. We compare dispersion between a wide range of statisticallyhomogeneous and stationary turbulent flows ranging from homogeneous isotropicNavier-Stokes turbulence over different configurations of magnetohydrodynamicturbulence and Boussinesq convection.