Convective Turbulence in a Cubic Cavity under Nonuniform Heating of a Lower Boundary

Abstract

The problem of heat transfer intensification using spatially nonuniform boundary conditions is of great interest. In this paper, the influence of a nonuniform, nonperiodic distribution of heating on the flow structure and convective heat flux for developed turbulent regimes (Ra = 1.1 × 109) is studied. The numerical simulation of convective turbulence in a cubic cavity is performed for a nonuniform heating distribution at the lower boundary using open-source software the OpenFoam 4.1. Calculations were carried out for three types of the temperature distribution: localized heating at the center of the lower boundary; nine heaters of the same size, equidistant from each other; and fractal heating. The heating area is the same in all of these distributions. It is shown that in all cases of a nonuniform heating distribution in the cavity a large-scale circulation is formed. The dynamics and structure of large-scale circulation depend on the temperature distribution at the lower boundary of the cavity. Spontaneous reorientations of the large-scale circulation plane by angles of ±45° or ±90° are revealed. A comparison of the intensity of the heat flux through the layer (cavity) at a fixed temperature difference at horizontal boundaries is made. It is shown that the heat transfer intensity weakly depends on the temperature distribution on the lower boundary. The maximum difference in the Nusselt numbers for three types of the nonuniform temperature distribution did not exceed 5%. Comparison of numerical simulation results for the uniform and nonuniform heating distributions at Ra = 1.1 × 109 shows that a decrease in the heating area by 70% leads to a decrease in the Nusselt number by 10%. It is shown that the heat flux also decreases with decreasing heating area, at fixed temperatures in the heating and cooling regions, not proportionally to the change in the area. For practical applications, an important role is played by the stability of the heat flux, which is characterized by the absence of pulsations. It is shown that the use of fractal heating can significantly reduce the level of heat flux pulsations without losses in the efficiency of heat transfer.