Stratification-confined Rayleigh-Taylor mixing

We study the Rayleigh-Taylor (RT) instability from an unstable interface, confined on either side by two stable density stratifications. Low Atwood number experiments were performed in a tank with an aspect ratio of O(1). The turbulent mixing region that develops due to a RT instability grows in time until the system reaches some stable configuration. We are interested in what governs this final stable state: the vertical extent and density structure of the mixed region, and the redistribution of energy in the system. One method of studying the latter is by examining the mixing efficiency, the proportion of kinetic and potential energy that is not dissipated but instead used to rearrange the probability density function of the density field. In a configuration with two homogeneous layers, the mixing efficiency cannot be higher than 50%. We find that much higher mixing efficiencies are achievable (more than 68%) when the mixing is not confined by geometry but instead by a stable stratification.