Flow reversals in low-Prandtl-number Rayleigh-Bénard convection controlled by horizontal circulations

We performed numerical simulations of Rayleigh-Bénard convection of an electrically conductive low-Prandtl-number fluid under a uniform horizontal magnetic field. We reproduced the flow reversals observed in laboratory experiments previously reported by us. The flow pattern is moderately constrained, as the axes of convection rolls tend to align in the direction of the horizontal magnetic field. The flow reversals occur when the intensity of horizontal circulation in a vessel exceeds a certain value, which induces bending and reconnection of convection rolls and causes rearrangement of these rolls. The wave number selection mechanism is responsible for the instability leading to the flow reversals. The total heat flow drastically decreases at the occurrences of reversal, reflecting the reduction of roll flow velocity. The irregularity of the reversal sequence and the change in symmetry in the flow pattern during the reversals are consistent with that in cessation-led flow reversals.