Statistics of two-particle dispersion in two-dimensional turbulence

We investigate Lagrangian relative dispersion in direct numerical simulation of two-dimensional inverse cascade turbulence. The analysis is performed by using both standard fixed time statistics and an exit time approach. The latter allows a more precise determination of the Richardson constant which is found to be gsimilar or equal to4 with a possible weak finite-size dependence. Our results show only small deviations with respect to the original Richardson's description in terms of diffusion equation. These deviations are associated with the long-range correlated nature of the particles' relative motion. The correlation, or persistence, parameter is measured by means of a Lagrangian "turning point" statistics. (C) 2002 American Institute of Physics.