Convective turbulence in a cubic cavity with non-homogeneous heating at the lower boundary
DOI:
https://doi.org/10.7242/1999-6691/2019.12.1.2Keywords:
convection, turbulence, numerical simulation, OpenFoam, cubic cellAbstract
The problem of heat transfer intensification using non-homogeneous boundary conditions is of great interest. This paper presents a study of the influence of non-homogeneous, non-periodic distribution of heating on the flow structure and convective heat flux for developed turbulent regimes (Ra = 1,1·109). A numerical simulation of convective turbulence was performed for non-homogeneous heating distribution at the lower boundary in the cubic cavity using open software OpenFoam 4.1. Calculations were carried out for three types of temperature distribution: localized heating at the center of the lower boundary, nine heaters of the same size, equidistant from each other, and fractal heating. All three heating distributions have the same area. The results of numerical simulation showed that in all three cases of non-homogeneous heating distribution in the cavity a large-scale circulation is formed, the dynamics and structure of which depend on the temperature distribution at the lower boundary. Spontaneous reorientations of the large-scale circulation plane by angle ±45° and ±90° were revealed. A comparison of the intensity of heat flux through the layer at a fixed temperature difference at horizontal boundaries was made. It is shown that the intensity of heat transfer weakly depends on the temperature distribution at the lower boundary. The maximum difference in the Nusselt number for three types of a non-uniform heating distribution does not exceed 5%. Comparison of the results of numerical simulation with a uniform and non-uniform temperature distribution for Ra = 1,1·109showed 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 decreases with decreasing heating area, at fixed temperatures in the heating and cooling areas, not proportionally to the change in area. For practical applications, an important role is played by the stability of the heat flow, 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 losing heat transfer efficiency
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