795 / 2024-09-19 14:24:05

Nonlinear energy cascade in coastal circulation

Numerical simulation,Turbulent Flow,vortex shedding,energy flux

Understanding how energy travels through a turbulent system, both spatially and with respect to flow scales, is essential in the context of coastal areas where different forcing and geophysical features interact to generate vortical structures known to play a fundamental role in momentum, mass and energy transport. Indeed, coastal zones are characterized by a wide range of interacting physical processes, including tides, waves, currents and human activities, all of which contribute to turbulence. In return, turbulence significantly affects sediment transport, nutrient distribution and ecosystem performance: understanding flow scales, ranging from large-scale ocean currents to small eddies, provides insight into how energy is transferred and dissipated within the system. Spatially, the distribution of energy affects how physical processes interact with coastal infrastructure and natural habitats. The classical methods for analyzing how the energy flows through the different scales consisted in using the Fourier spectral analysis. Although the method has provided significant insights, it is largely restricted to quasi-homogeneous regions with simple boundary conditions, often requiring special treatment at the boundaries. On the other hand, the filter-space technique (FST) has been introduced in several studies and has found wide and successful application in turbulent flow analysis. Unlike Fourier spectral analysis, FST preserves the spatial distribution and direction of fluxes, offering a clear indication of whether a process exhibits a direct or inverse energy/enstrophy cascade. In this study, nonlinear energy transfers are studied starting from a dataset of numerical ocean and costal circulations in the Great Bay Area, generated by different forcing (wind, pressure and tides). Our study shows that, depending on the geophysical forcing, the classical direct energy cascade does not always hold, but that energy can also flow from small to larger scales in an inverse cascade.