Evidence of transient energy and enstrophy cascades in tidal flows : a scale to scale analysis

Abstract

Tidal currents are predominant in coastal areas, causing the generation of vortices at different scales. We reproduce the main process of vortex shedding generated in tidal systems with inlets and channels using a laboratory large-scale model. A filter-space technique is implemented to analyze nonlinear energy/enstrophy transfer rates and map out the energy pathways through the flow scales of the measured velocity fields. We provide sound evidence of the transitional character of the energy cascades during a tidal period. The periodic generation and destruction of tidal vortices plays a relevant role in the transition from an inverse to a direct energy cascade within a tidal period. The period-averaged energy budget shows the coexistence of multiple cascades. Small scales follow a direct energy cascade, whereas a split-energy cascade is found at intermediate and large scales, where part of the injected energy goes to small scales and part to a larger flow scale.