Observations of large-scale coherent structures in gravity currents: implications for flow dynamics

Abstract Density driven flows, also known as gravity currents, comprise a head, body, and tail. Yet whilst the body typically forms largest part of such its structure remains poorly understood. In this work, experimental data gathered using particle image velocimetry enables instantaneous, whole-field dynamics constant-influx solute-based currents to be resolved. While averaged turbulent kinetic energy profiles are comparable previous instantaneous sets reveal significant temporal variation, with velocity measurements indicating large-scale wave-like motions within body. Spectral analysis dynamic mode decomposition, streamwise vertical velocity, used identify frequencies structures dominant flow. By considering an idealised theoretical density profile, it is suggested that these may internal waves form critical layer flow located at height maximum velocity. Irreversible wave breaking has been postulated occur suggests formation eddy transport barriers, demonstrating new models mixing in needed. Graphic abstract