Three-Dimensional Numerical Simulation Research on Discharge Characteristics of Storm-Drain Inlet in Low-Lying Areas

Storm-drain inlets can lessen surface runoff and are essential for managing urban flooding. To fully grasp the storm-drain inlet discharge characteristics, a computational fluid dynamics (CFD) method was utilised to research. In this study, the discharge characteristics of 36 groups of storm-drain inlets with various water depths and flow velocities were simulated separately. This paper systematically analysed the distribution characteristics of flow patterns, streamlines and velocities of storm-drain inlets. The findings indicate that: the distribution of streamlines and the shape of the free water surface within the storm-drain inlet change significantly with increasing incoming water depth; the flow pattern in the vicinity of rainwater wells changes from the free weir flow to the submerged weir flow; the free water surface of the storm-drain inlet transitions from the state of being partially to entirely covered by water flow. The empirical formula between the discharge coefficient of the storm-drain inlet and the Froude number was constructed by dimensional analysis with a high correlation coefficient. And compared with other empirical formulas, the formula considers the effects of different factors on the discharge capacity of storm-drain inlets in a relatively comprehensive way. This research’s results help deepen the awareness of the discharge process at storm-drain inlets and have implications for guiding municipal flooding management.