Groins are typical hydraulic structures commonly found in rivers, exerting a substantial influence on flow patterns and channel morphology. Given the frequent and significant variations in water depth in natural rivers, it is essential to understand how coherent flow structures and mass exchange characteristics respond to different shallowness conditions. This study employs numerical simulations to investigate mass exchange processes and the associated coherent flow structures, including mixing layers, secondary flows, and vortex dynamics. The investigation covers a range of flow conditions, from shallow flows with emergent groins to deep flows with submerged groins. The results reveal that coherent flow structures exhibit distinct characteristics under different scenarios, resulting in varying dominant mechanisms of mass exchange. Under shallow water conditions, the mixing layer governs mass exchange, whereas in deeper and submerged cases, secondary flows and enhanced three-dimensional vortex motions become increasingly influential. These findings provide insight into the flow dynamics, mass, and material transport patterns induced by groins in riverine environments, as well as related ecological problems and river restoration works.
Dong et al. (Thu,) studied this question.
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