SCALE DEPENDENCE OF THE STATISTICAL CHARACTER OF TURBULENT FLUCTUATIONS IN THERMAL-CONVECTION

Two numerical realizations of thermal turbulence at Ra = 630 000 and at the disparate aspect ratios (AR) of 3.1 and 6 were shown previously [Phys. Fluids A 5, 412 (1993)] to exhibit probability distribution functions (PDFs) of temperature flucuations (T'), which were exponential in the former case and Gaussian in the latter. Such PDFs for T' are instrumental in definitions of hard and soft turbulence regimes. Here the same two realizations are considered, but the fields are spectrally decomposed by a horizontal scale before accumulating statistics. Within either flow field, both Gaussianity and exponentiality are present, but at differing lateral scales. The T' distributions are seen to be Gaussian in the large scales, and the exponential at the small ones with parallel trends seen in the statistics of the velocity fields. Similarities with previous experimental and theoretical results and implications for soft/hard turbulence classification are discussed.