Temporal statistics in high Rayleigh number convective turbulence

Temporal statistics of temperature and velocity fluctuations are studied in a highly turbulent convective flow developed within a cylindrical cell of aspect ratio Γ=1/2. Numerical data are analyzed for Ra up to 2×10^11 at fixed Prandtl number (Pr=0.7). Temperature and velocity time series are collected from numerical probes placed within the fluid volume in the bulk and close to the boundaries. It is shown that the effects of the boundaries and of the large scale recirculation are reflected in the temporal statistics of the analyzed quantities. Spectra and structure functions show that the temperature statistics follow the Bolgiano scaling while the velocity fluctuations exhibit scaling laws which are surprisingly very close to those of the temperature. These results are in contrast with the Bolgiano or Kolmogorov behaviors expected for the velocity statistics and a possible theoretical explanation is presented.