Lagrangian Measurements in Turbulent Thermal Convection: About the Inhomogeneity of the Velocity and Temperature Fields

Turbulent thermal convection is a complex problem: the flow is forced at almost all scales, because of the presence of both large scale circulation and small scale plumes. Moreover the difference of density induced by temperature adds an ingredient in the basic equations of the flow, so that turbulence could be different from the case of pure mechanical forcing. Mixing is in principle different and probably increased because of the structure of the plumes. Moreover the entire flow is not homogeneous (at least at large scales) and the statistical behaviour can be influenced by the large scale flow. One way to probe all these specific effects is to use a Lagrangian point of view, measuring, for example, Lagrangian transport of velocity and temperature, or heat flux. We will show how the inhomogeneity of the mean temperature and velocity fields affect the heat flux. Then the interactions between the mean fields and the Lagrangian fluctuations will be highlighted.