A comparative study of the turbulent Rayleigh-Taylor (RT) instability using high-resolution 3D numerical simulations: The Alpha-Group collaboration

The turbulent RT instability is investigated in the limit of strong mode-coupling using a variety of high-resolution, multi-mode, three dimensional (3D) numerical simulations (NS). The perturbations are initialized with only short wavelength modes so that the self-similar evolution (i. e. bubble diameter D b µ amplitude h b) occurs solely by the nonlinear coupling (merger) of saturated modes. After an initial transient, it is found that h b ~ a b Agt 2 where A = Atwood number, g = gravity and t = time. The NS yield D b ~ h b /3 in agreement with experiment but the simulation value a b ~ 0.025 ± 0.003 is smaller than the experimental value a b ~ 0.057 ± 0.008. By analyzing the dominant bubbles, it is found that the small value of a b can be attributed to a density dilution due to fine-scale mixing in our NS without interface reconstruction (IR) or an equivalent entrainment in our NS with IR. This may be characteristic of the mode coupling limit studied here and the associated a b may represent a lower bound that is insensitive to the initial conditions. Larger values of a b can be obtained in the presence of additional long wavelength perturbations and this may be more characteristic of experiments. Here, the data from the NS are also analyzed in terms of bubble dynamics, energy balance and the spectra of density fluctuation.