231 / 2024-02-28 13:28:58

Modeling flow structure around a channel-centered vegetation patch with streamwise extension

Vegetation patch elongation,flow adjustment,LES modeling,vortex formation

Aquatic vegetation commonly grows in patches at early succession periods, playing a critical role in mediating hydrodynamics, geomorphodynamics and surface water ecosystem. The structures of mean flow and wake around a vegetation patch have been extensively explored experimentally and numerically. However, the adjustment of these flow structures due to the streamwise extension of the patch remains poorly understood, which hampers effective management of the surface water system utilizing aquatic vegetation. This study employs a depth-averaged large eddy simulation (DA-LES) model to investigate the effect of patch length on the flow structure around a rectangular vegetation patch located at the channel center. The observed longitudinal profiles of mean flow velocity along the center axis of the patch are used for model validation. Our results demonstrate that the DA-LES model can effectively capture the interior flow adjustment within the patch as well as downstream wake structure as the patch grows in length. Notably, our modeling accurately visualize the vortex evolution from the along-edge Kelvin-Helmholtz (K-H) vortices to after-patch Karman vortices. Furthermore, our finding indicates that increasing patch length can trigger the formation of wake Karman vortices despite lower patch density if cumulative vegetation resistance exceeds a certain threshold required for triggering such vortices. Additionally, DA-LES modeling provides valuable insights into interactions between different types of vortices around elongated patches and enhances understanding of mean flow behavior of the wake. The results from the present study and future further research are useful for predicting contaminant dispersion as well as sediment dynamics within the wake region of a vegetation patch with variable lengths.