Experimental Investigation of Rayleigh-Benard convection in a liquid metal layer exposed to a horizontal magnetic field

Rayleigh-Benard convection has been investigated inside a liquid metal layer under the influence of a DC magnetic field. Similar configurations can be found in geophysical or steel production. Our group reported recently that spontaneous flow reversals of quasi two-dimensional rolls randomly occur in Rayleigh-Benard convection of liquid metal exposed to a horizontal magnetic field (Yanagisawa, et al., PRE, 2011). In fluid layers with relatively large aspect ratios the flow pattern consisting of several convection rolls appears to be almost isotropic. However, the rolls are aligned with the magnetic field direction if the Lorentz force becomes either comparable to the buoyancy or larger. In our experiment, where the fluid layer has a dimension of 200x200x40 mm (corresponding to an aspect ratio of 5), the convection pattern can show 3, 4 or 5 rolls regimes depending on the Rayleigh number Ra and the Chandrasekhar number Q. Flow reversals occur spontaneously between these steady states in the Ra-Q parameter space.