Experimental measurements of spatiotemporal-resolved energy dissipation rate in turbulent Rayleigh–Bénard convection: Rayleigh number dependence and statistical properties*

We obtain the spatiotemporal-resolved energy dissipation rate, for the first time, using our velocity gradient tensor resolved particle image velocimetry (VGTR-PIV) system in turbulent Rayleigh–Bénard convection. The power-law scaling of the time-averaged energy dissipation rate with Rayleigh number follows 〈ε_c〉_t∽Ra^1.54±0.02, 〈ε_s〉_t∽Ra^1.25±0.02, 〈ε_b〉_t∽Ra^1.23±0.02 and 〈ε_w〉_t∽Ra^1.25±0.02 in the center, side, bottom and wall regions, respectively, providing important constraints against which theoretical models would be validated. The probability density functions (PDFs) of the energy dissipation rate and enstrophy largely follow a stretched exponential distribution and deviate significantly from a log-normal distribution. Extreme events with high dissipation or vorticity are most intermittent in the side region, and the bottom region is less intermittent than the cell center. Exponential distributions of both dissipation rate and enstrophy PDFs exist in the bottom region at low Ra. The exponential distribution is an inherent property in near-wall regions, as confirmed by the conditional analysis and the wall energy dissipation rate PDF.