Travelling of a reflecting immersed disc in a convective layer heated by incident radiation

Abstract

The two-dimensional motions of a disc submerged at a fixed depth but floating freely in an extended layer of liquid heated by a radiation flux falling from above are studied. The motion of a body in a convective layer depends on a number of factors such as the size of the body, the geometry of the cavity and the physical properties of the fluid and the body. The main focus of this work is to reveal the role of the degree of homogeneity of the distribution of heating of the underlying surface by incident radiation. Numerical simulations allowed us not only to describe the motion of the disc, but also to show the full three-dimensional structure of the convective flow for different regimes. Verification laboratory experiments confirmed the adequacy of the numerical simulations and clarified the role of the optical properties of the floating body. The simulation results showed the sensitivity of the system to the homogeneity of the radiation flux. A change in the radiation distribution leads to a change in the structure of the large-scale circulation. In the case of homogeneous distribution, a toroidal vortex is formed with the liquid sinking in the central part, and in the case of inhomogeneous distribution with maximum heating in the centre, on the contrary, a vortex appeared with the liquid rising in the centre. Since the motion of a floating body is determined by large-scale flows, their rearrangement leads to qualitative changes in the spatial and temporal characteristics of the disc motion. The experiments with discs of different radiation transparency demonstrated that, when the transparency coefficient reaches 0.4, the wandering of the disc stops.