SINOPSIS

Fluctuating local dissipation scales for turbulent Rayleigh–Bénard (RB) convection are investigated using the lattice Boltzmann method (LBM) at different Rayleigh numbers (Ra). Special attention is paid to the fluctuating local dissipation scales for turbulent RB convection, the probability density function (PDF) of the local dissipation scale and PDF of the dissipation rates at different Ra. It is observed that a further increase of Ra tears off unstable spokes to form more independent large-scale flow structures generated in the thermal boundary layers and driven by buoyancy. It is validated that the fluctuations of the energy dissipation field can directly be translated into a fluctuating local dissipation scale, which is found to develop ever finer fluctuations with increasing Ra. It is noted that the scales in the whole cell cover a wider range, both to the large-scale and small-scale end which is centered around the most probable value.