Timescales of energy transfer in self-similar Rayleigh-Taylor turbulence

In temporally growing Rayleigh-Taylor (TRT) flows, the mixing layer height increases over time while the Kolmogorov scales become progressively smaller. As the range of length scales broadens with Reynolds number, so does the cascade time between the production of turbulent kinetic energy at the large scales and its eventual dissipation at the smallest scales. Although this extended cascade time is often cited as the primary reason for the deviation of TRT flow statistics from equilibrium-based turbulence models, it has not been directly quantified, likely due to the difficulty of extracting timescale information from inherently non-stationary signals. To address this challenge, the statistically stationary RT (SRT) flow configuration is employed as an approximation of TRT turbulence dynamics. The SRT configuration generates continuous flow realizations of a single flow unit at a fixed Reynolds number, producing statistically stationary signals across all flow quantities. Correlation times are extracted from time-series data of dominant terms in the mixed mass budget, as well as the vertical and in-plane components of the turbulent kinetic energy budget. This analysis reveals key energy transfer mechanisms in RT turbulence and quantifies the associated timescales across Reynolds numbers and Atwood numbers. Finally, using the extracted timescales, methods are proposed to reconcile the non-stationary nature of TRT flows with equilibrium-based descriptions of turbulence.