Micro-Characteristics of Turbulent Thermal Convection in a Horizontal Fluid Layer Heated Internally and from Below

Measurements were taken of the fluid temperature fluctuations with turbulent thermal convection in a horizontal layer of water with uniform volumetric energy sources and a constant rate of bottom heating. The temperature fluctuations were fairly small in the central core region, which was nearly isothermal because of strong turbulent mixing. At the edge of the thermal boundary layer, however, violent temperature spikes were dominant, and were accompanied with the intermittent release of cold plumes from the upper boundary and hot plumes from the lower boundary. With an increase in the Rayleigh number, the number of plumes per unit area increased and the frequency of plume formation became higher. The measured surface heat flux agreed well with the calculation by a theoretical model, in which a renewal of the heat-generating boundary layer was assumed to occur periodically at the moment of plume release.