Low-frequency oscillations under conditions of non-uniform thermal convection
M.S. Bobrov, M.Yu. Khrebtov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: thermal convection, non-uniform heating, coherent structures, direct numerical simulation
Abstract
The results of direct numerical simulation (DNS) of the influence of a horizontal surface temperature gradient on the dynamics of a thermal convective flux are presented. A series of simulations was performed at moderate Rayleigh numbers (105 - 108). The computational domain was rectangular and its two horizontal walls had a specified average temperature difference, leading to the formation of a free-convective flow. The temperature on the lower wall was nonuniformly distributed along one of the horizontal axes. Convective cells formed due to the vertical density gradient were subject to a weak horizontal temperature gradient, which led to their deformation and transfer toward the central axis of the computational domain. As a result, intense coherent horizontal oscillations in the position of the central upflow at a low frequency were observed. This frequency depended weakly on the Rayleigh number, and the oscillation amplitude increased with its increase. This low-frequency oscillation effect is not evident in two-dimensional modeling and arises from the interaction of adjacent three-dimensional convective cells entering the central upflow. The authors propose an asymptotic estimate for the period of these oscillations. It is shown that the oscillations do not disappear with increasing Rayleigh number, suggesting their influence on heat and mass transfer in natural flows.
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