Near-field flow dynamics of grate inlets during urban floods

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The accurate characterization of near-field flow dynamics from urban surface to sewer system is essential for the design of urban drainage systems and the risk identification of urban floods. Motivated by the observation that the vortex flow structure was evident around the grate inlet during urban flood events, a physical model was used to measure flow features and investigate the drainage capacity of grate inlets. Detailed flow velocity fields and flow motions in the vicinity of the grate inlet are presented in both horizontal and vertical directions. It is found that there exists a critical threshold of water depth at 0.05 m, where the flow regime transforms from weir flow to orifice flow for the tested grate inlet. In addition, flow accelerates significantly near the grate inlet and the vortex flow feature is obviously enhanced from the surface layer to the bottom layer in the region of the grate inlet. With the decrease in discharge capacity, vortex flow structure and turbulence kinetic energy were intensified significantly. Overall, this work demonstrates the near-field flow dynamics of grate inlets and the experimental datasets could also be helpful for the design of drainage systems and the validation of numerical modeling in various urban flood events.