Enhanced flushing in long emergent vegetation with two flow parallel interfaces: simulation and predictive modeling at moderate Reynolds number

Emergent vegetation with two stream-parallel interfaces leads to the enhanced reduction in contaminants retention time due to the exchange of cross-array vortex communication in vegetative patches. To investigate this phenomenon, in this study, we numerically simulate 2-dimensional (D) flow through an array of circular cylinders consisting of a channel in between. We use flow diagnostics to understand the complex interaction of wakes for various moderate Reynolds number (Re). The vortex identification techniques reveal that the vortex pairing mechanism is responsible for energetic vortical structures at higher Re. We then incorporate the velocity field into a Lagrangian particle tracking simulation, which includes advection and molecular diffusion. We observe that the transverse spreading of the tracer plume is enhanced with increasing Re. The tracer breakthrough curves (BTCs) obtained for a two-sided parallel flow interface show a significant increase in flushing relative to a one-sided parallel interface array at the higher Re. This suggests that two flow-parallel interface leverages additional vortex strength in reducing the residence time within the array of a circular cylinder. Finally, we upscale BTCs using a continuous-time random walk model parameterized with a particle tracking and numerical simulation.