Mixing and layering at the interface of a two-layer fluid forced by random jets

Understanding mixing at density interfaces is essential for predicting transport in stratified environmental flows. Laboratory studies have mostly relied on steady, spatially uniform forcing, whereas turbulence in nature is intermittent and heterogeneous. Here, we present experiments on a two-layer salt-stratified fluid forced by random turbulent bursts generated with a Randomly Actuated Synthetic Jet Array (RASJA). Density fields are measured with the light attenuation technique, allowing us to resolve the interface evolution. We find that the upward velocity of the interface follows a power-law dependence on the density jump, in agreement with previous oscillating-grid studies. At large density differences, the interface sharpens during mixing, consistent with the Phillips–Posmentier layering mechanism, while at smaller density jumps it broadens. Background potential energy analysis demonstrates irreversible mixing in both cases, with typical mixing efficiencies comprised between 6 % and 8 %. These results extend classical laboratory observations to a more isotropic forcing, offering new insights into the dynamics of mixing in geophysical settings.