3D chaotic model for sub-grid turbulent dispersion in Large-Eddy Simulations

A 3D multiscale kinematic velocity field is introduced as a model to simulate Lagrangian turbulent dispersion. The incompressible velocity field is a nonlinear deterministic function, periodic in space and time, that generates chaotic mixing of Lagrangian trajectories. Relative dispersion properties, for example Richardson’s law, are correctly reproduced under two basic conditions: 1) the velocity amplitudes of the spatial modes must be related to the corresponding wavelengths through the Kolmogorov scaling and 2) the problem of the lack of a “sweeping effect” of the small eddies by the large eddies, common to kinematic simulations, has to be taken into account. It is shown that, as far as Lagrangian dispersion is concerned, the model presented herein can be successfully applied as an additional subgrid contribution for large eddy simulations of the planetary boundary layer flow.