Berlin 2018 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 42: Turbulence

DY 42.6: Talk

Wednesday, March 14, 2018, 11:30–11:45, BH-N 128

Directed locomotion fuelled by turbulent fluid motion — Nicolas Francois, Hua Xia, Horst Punzmann, and •Michael Shats — Centre for Plasmas and Fluids, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia

Chaotic horizontal motion of fluid at the liquid-gas interface is a ubiquitous phenomenon since such a motion can be driven by surface waves. When waves are steep, such motion is not just chaotic. It becomes turbulent in the sense of Kraichnan's two-dimensional turbulence, a state strongly out of equilibrium. We show that a properly shaped floating object on the liquid surface can tap energy of turbulent fluctuations to fuel its self-propulsion along a trajectory which can be viewed as a rectified random walk. If a floating device is fixed at one position on the surface, making a horizontal rotor, it can convert turbulent fluctuations into unidirectional rotation. The effect relies on the momentum transfer from the underlying fabric of the flow to the floating object. The shape of the object controls its ability to become a 'Lagrangian ratchet' that can tap the energy of correlated bundles of fluid trajectories.