TURBULENT FLOW AND TRANSPORT IN OPEN CHANNELS WITH NATURAL ROUGHNESSES: EXPERIMENTS AND NUMERICAL SIMULATIONS

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The presence of submerged vegetation in conveyance channels leads to an increase in flow resistance and reduction of channel flow capacity. For this reason, vegetation has often been removed from channel beds. Biologists and ecologists have recognized that submerged vegetation can provide a wide range of important ecosystem services. Aquatic vegetation helps reduce turbidity, remove nutrients, produce oxygen and alter sediment transport. Studying the interaction of turbulence with aquatic vegetation and its role in cycling nutrients, controlling erosion, and protecting riverbanks can have enormous ecologic and economic benefits. The fluid flow-plant interaction can be quite complex. Aquatic plants and the shear-layers that they generate can occupy a significant fraction of the total flow domain. The submerged plants can be flexible, coupling the motion of the fluid and the canopy. Besides being buoyant, flexible canopies can exhibit a coherent waving in response to the flow. The morphology of the vegetation can also play an important role in the posture due to the stem stiffness, which can influence the drag. A combined effect of stem stiffness, blade shape, positioning and their interaction with the flow is still not well understood. A universal description of drag for flexible aquatic vegetation remains elusive. The present research program is a step towards better understanding of the interaction of clusters of submerged vegetation and turbulence in open channels. The major goals include: (1) To study the major features of flow, turbulence and transport associated with flexible and rigid vegetation via experiments and numerical simulations and (2) To quantify the drag in the case of flexible vegetation that appear vital for understanding the fluid-plant interaction. (3) The fluid dynamics of finite patches of flexible and rigid vegetation and (4) Investigation of turbulence and coherent structures in the wake of the patch. Besides training HQP and influencing policy makers, the proposed research will also have a positive influence on other Windsor research programs as the numerical and experimental tools assembled for this project can be successfully employed in other investigations.