Local dissipation scales in two-dimensional Rayleigh-Taylor turbulence.

We examine the distribution of the local dissipation scale η, Q(η), and its temporal evolution in two-dimensional (2D) Rayleigh-Taylor (RT) turbulence using direct numerical simulations at small Atwood number and unit Prandtl number. Within the self-similarity regime of the mixing zone evolution, distributions of η at small scales are found to be insensitive to the large-scale anisotropy of the system and independent of position and of the temporal evolution of the mixing zone. Our results further reveal that the present measured Q(η) agrees with those previously observed in homogeneous isotropic turbulence and in turbulent pipe flows, at least for the smallest scales around the classical Kolmogorov dissipation scale. However, the RT case seems to show a different trend from the other two cases for large scales, which may attributed to the absence of the inertial-range intermittency for the velocity field in 2D RT turbulence.