Tidal flow past an island : Eddies and energy dissipation

What is it about?

High resolution numerical simulations show that strong tidal flows modulate the flow characteristics in the vicinity of islands. For example, it can change the frequency of occurrence of low pressure zones behind the island. We present high-resolution three-dimensional simulations of the interaction of a tidally modulated current with a model submerged hill where the magnitude of the tidal flow relative to the steady current is varied. Results show that relatively small tidal currents can modify the process of eddy formation in the wake of the obstacle, changing the eddy shedding frequency from its natural value. The shedding rate decreases as tidal magnitude is increased until the interval synchronizes to twice the tidal period. We find significant loss of kinetic energy in the wake of the obstacle, along its sides and near its crest, with maximum values occurring when the peak tidal current coincides with the steady flow. Energy dissipation increases sharply with increasing tidal current magnitude.

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Photo by Zunnoon Ahmed on Unsplash

Photo by Zunnoon Ahmed on Unsplash

Why is it important?

The flow near an island is crucial for its climatology and governs activities such as fishing in its vicinity. Strong tidal oscillations introduce changes to these flow patterns, thereby affecting the economics of voyages.

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