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Dresden 2017 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 16: Focus: Fundamental aspects of turbulent convection

DY 16.4: Talk

Tuesday, March 21, 2017, 10:30–10:45, ZEU 118

The effect of a horizontal magnetic field on weakly turbulent Rayleigh-Benard convectionVogt Tobias1, Ishimi Wataru2, Tasaka Yuji2, Yanagisawa Takatoshi3, and •Eckert Sven11Helmholtz Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany — 2Laboratory for Flow Control, Hokkaido University, Sapporo, Japan — 3Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan

MHD Rayleigh-Bénard convection was studied experimentally using the eutectic metal alloy GaInSn inside a box having a square horizontal cross section and an aspect ratio of length/height = 5/1. Systematic flow measurements were performed by means of ultrasound Doppler velocimetry that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two dimensional rolls arranged parallel to the magnetic field. If the Rayleigh number (Ra) is increased over a certain threshold Ra/Q, whereby Q is the Chandrasekhar number, the convection flow undergoes a transition to turbulence. Besides the primary convection rolls the flow measurements reveal regular flow oscillations arising from 2D and 3D deformations of the rolls, Ekman-pumping induced flow as well as smaller side vortices that develop around the convection rolls. The experiments are accompanied by direct numerical simulations. The comparison between the DNS and the flow measurements shows a very good agreement.

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