Berlin 2018 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 42: Turbulence

DY 42.7: Talk

Wednesday, March 14, 2018, 11:45–12:00, BH-N 128

Tuning diffusion of finite size particles in turbulent flows — •Hua Xia, Nicolas Francois, Horst Punzmann, and Michael Shats — Research School of Physics and Engineering, The Australian National University, Canberra, Australia

The motion of a large floater on a liquid surface perturbed by Faraday waves was shown to be erratic and share features similar to the Brownian motion of particles in contact with a thermal bath. In particular a fluctuation-dissipation relationship was uncovered. This similarity with systems at thermodynamic equilibrium seems at odds with the fact that Faraday waves generate turbulent flows, a state strongly out of equilibrium.

Here we show that the law of dispersion in chaotic flows can be widely tuned due to the coupling of diffusing particles with the fabric and memory of the flow. We demonstrate a sharp change in the law of diffusion as a function of scales seen as a transition from *thermal* diffusion at large scales to strongly non-equilibrium regime at small scales. The chaotic flow is dominated by underlying coherent bundles executing random walk. Large particles interact with many bundles, disperse similar to a Brownian particle in a thermal bath. For particles smaller than the characteristic length scale, the coherent bundles push the particles resulting in a much faster dispersion.