Experimental investigation of pair dispersion with small initial separation in convective turbulent flows

摘要

We report an experimental investigation of pair dispersions in turbulent thermal convection with initialnseparation r0 ranging from sub-Kolmogorov scale to scales in the inertial range. In the dissipative range ofnscales we observed the exponential growth of the separation between a pair of particles predicted by Batchelornand obtained a Batchelor constant 0.23 ± 0.07. For large r0, it is found that, for almost all time ranges, both thenmean-square separation and distance neighbor function exhibit the forms predicted by Batchelor, whereas thentwo quantities agree with Richardson’s predictions for small r0. Moreover, the measured value of the Richardsonnconstant g = 0.10 ± 0.07, which is smaller than those found in other turbulence systems. We also demonstratenthe crossover of the mean-square separation from the exponential to the Batchelor regimes in both temporal andnspatial scales.