RESUMEN
We study the problem of heat transport by fluid flows with prescribed velocity fields. The advection-diffusion equation in two dimensions is solved for two velocity fields: (i). a circulation and (ii). a shear flow. These two flows focus separately on the two dominant features of the mean large-scale flow observed in turbulent convection experiments. We find that the Nusselt number, which measures the heat transport, scales respectively for the two velocity fields.
RESUMEN
We find that the conditional statistics of temperature difference at fixed values of the locally averaged temperature dissipation rate in turbulent convection become Gaussian in the regime where the mixing dynamics is expected to be driven by buoyancy. Hence, intermittency of the temperature fluctuations in this buoyancy-driven regime can be solely attributed to the variation of the locally averaged temperature dissipation rate. We further obtain the functional behavior of these conditional temperature structure functions. This functional form demonstrates explicitly the failure of dimensional arguments and enhances the understanding of the temperature structure functions.