A random 2D walk of a submerged free-floating disc in a convective layer

Abstract

Free motions of a thermally insulating disc submerged in a liquid layer heated from below are studied experimentally. The disc is fixed at a certain height from the bottom of the convective cell, but can move freely in horizontal directions. Blocking of vertical motion and heat flux leads to the appearance of large-scale vortices, which in turn, drags the disc. The interplay of the large-scale circulation and the disc produces complex two-dimensional disc motions. The disc dynamics is mainly determined by large-scale modes: toroidal vortex with descending fluid in the centre and large-scale vortices along each coordinate, existing on the background of intense, but relatively short-lived small-scale convective cells. The wandering disc forms a cold spot above itself, which affects large-scale circulation but has little effect on cell convection at scales on the order of the layer thickness, which provide the main heat transport and dominate the upper part of the layer. Despite the essentially three-dimensional flow structure, which is fundamentally different from that of the convective flow in an elongated tank with one-dimensional disc motions, the travels along each coordinate look similar to one-dimensional motions.