Jump rope vortex in liquid metal convection

Abstract

Understanding large-scale circulations (LSCs) in turbulent convective systems is important for the study of stars, planets, and in many industrial applications. The canonical model of the LSC is quasi-planar with additional horizontal sloshing and torsional modes [Brown E, Ahlers G (2009) <i>J Fluid Mech</i> 638:383-400; Funfschilling D, Ahlers G (2004) <i>Phys Rev Lett</i> 92:194502; Xi HD et al. (2009) <i>Phys Rev Lett</i> 102:044503; Zhou Q et al. (2009) <i>J Fluid Mech</i> 630:367-390]. Using liquid gallium as the working fluid, we show, via coupled laboratory-numerical experiments in tanks with aspect ratios greater than unity ([Formula: see text]), that the LSC takes instead the form of a "jump rope vortex," a strongly 3D mode that periodically orbits around the tank following a motion much like a jump rope on a playground. Further experiments show that this jump rope flow also exists in more viscous fluids such as water, albeit with a far smaller signal. Thus, this jump rope mode is an essential component of the turbulent convection that underlies our observations of natural systems.