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I will discuss the problem of turbulent pair dispersion of neutrally buoyant (tracer) and heavy particles, i.e. the way two particles separate in a turbulent flow. In the case of tracers only, there is a classical theory, which is due to L. F. Richardson (1926): it is in terms of a diffusion equation for the relative separation distribution, with a scale dependent diffusion coefficient. As a result, relative dispersion of pairs of tracer particles in a turbulent flow is a globally self-similar in time process. Experimental and numerical evidences show the existence of large and intermittent fluctuations, pointing to a limited applicability of such an approach. To illustrate the key questions in the topic, I will present recent results from high resolution direct numerical simulations, and then discuss research directions in the problem.
This work is done in collaboration with L. Biferale, R. Scatamacchia and F. Toschi. |