Modeling particle dispersion in a turbulent puff*

In this work we consider particle dispersion in a turbulent pulsed jet. Unresolved subgrid-scale velocity fluctuations in coarse-grained simulations like large-eddy simulation and Reynolds-averaged Navier-Stokes play a significant role in particle dynamics. Stochastic models are commonly used to model the subgrid-scale velocity fluctuations 'seen' by particles as they have proven effective in recapturing one-point and two-time statistics. However, state-of-the-art continuous random walk models lack spatial correlation, leading to the loss of two-point statistics and geometric features such as clustering and preferential concentration. We present a two-point Lagrangian stochastic model designed to capture spatial particle distributions and maintain the one-point and two-time capabilities of classical stochastic models. Model coefficients are chosen to reproduce the correct scaling of particle-pair relative statistics. Comparisons of particle dispersion and preferential concentration between direct numerical simulations, large-eddy simulations, and experimental data demonstrate the utility of stochastic models and the need for a two-point formulation.