Effects of rotation on kinetic energy and enstrophy in Rayleigh–Taylor turbulence

The study of rotating Rayleigh–Taylor (RT) turbulence is of fundamental significance for geophysical processes and certain engineering applications. This work systematically investigates the effects of rotation on RT turbulence using direct numerical simulation (DNS), focusing primarily on the generation of kinetic energy and enstrophy, as well as the scale-to-scale transfer of kinetic energy. Based on the DNS results, it is demonstrated that there is a notable delay and inhibition of the mixing layer growth with enhancing rotation (quantified as a decreasing Rossby number, $Ro$ ). That is, energy conversion efficiency drops substantially, from approximately $50\,\%$ in the non-rotating case $Ro = \infty$ to only $10\,\%$ in the strong rotating case $Ro=0.1$ . This is because rotation amplifies the viscous dissipation associated with the shear stress components in the vertical direction within the mixing layer. Regarding enstrophy generation, baroclinic effects dominate during the early stage of flow evolution, while vortex stretching and tilting become the primary contributors in the later stage. Notably, the vortex stretching and tilting term is significantly suppressed by the rotation, resulting in three-dimensional RT turbulence exhibiting an enstrophy generation mechanism more akin to two-dimensional flow. Furthermore, analysis of scale-to-scale transfer of kinetic energy reveals an increased likelihood of local inverse energy transfer events under enhanced rotation. Specifically, strong rotation (e.g. $Ro=0.1$ ) results in strongly helical turbulence, which contains more high-helicity regions favourable for local inverse energy transfer. Moreover, the presence of rotation leads to more coherent and elongated flow structures and an enhanced efficiency of fluid mixing within the mixing layer.