Abstract

Reynolds number dependence including the effects of intermittency is a crucial issue in the study of Lagrangian statistics and in how information from direct numerical simulations can be useful for stochastic modeling. Intermittency in the form of localized regions of intense straining or rotation is, for example, expected to influence how rapidly a fluid particle undergoes acceleration, and how multiple diffusing fluid particles move apart from each other. An effective approach to delineate such effects is to compute Lagrangian statistics conditioned on energy dissipation rate, enstrophy, or pseudo-dissipation following fluid particle trajectories. In this talk we shall illustrate these issues via recent results from simulations of isotropic turbulence at Reynolds numbers sufficiently high for observing inertial range behavior in the Eulerian (but not necessarily Lagrangian) frame. We also discuss research directions in the near future, including flows of greater complexity, and the promise of simulations at ever-increasing grid resolution that rapid advances in computing power are expected to make feasible.