Cascades of velocity and temperature fluctuations in buoyancy-driven thermal turbulence.

Direct multipoint measurements of the velocity and temperature fields have been made in a turbulent Rayleigh-Bénard convection cell. In the central region of the cell it is found that both velocity and temperature exhibit the same scaling behavior that one would find for the velocity and for a passive scalar in homogeneous and isotropic Navier-Stokes turbulence. This is despite the fact that energy is pumped into the system vertically via buoyancy. Near the cell's sidewall where thermal plumes abound, vertical velocity and temperature exhibit different scalings. A model that takes into account both buoyancy and energy dissipation is proposed and its predictions agree well with the sidewall experimental results.