Tangential intake structures with vertical dropshafts are commonly employed in stormwater and urban drainage systems. Vortex and plunging flows are the two typical flow patterns observed in dropshafts, with the former being the desired due to its favourable drainage performance and enhanced safety. The transition between these flow patterns is primarily influenced by the structural design and rate of flow discharge. To investigate the interception performance and the transition criteria between vortex and plunging flows, a series of numerical simulations were conducted. The effects of the approach channel slope, contraction ratio, and flow discharge were analyzed by comparing the evolution of the water surface, pressure and velocity distributions, and swirling distance across various scenarios. With a higher flow rate of 20 L/s, obvious water congestion was observed in dropshafts with contraction ratios below 0.4 and horizontal approach channels. However, the inflow channel was not congested in cases with sloping approach channels, indicating higher drainage efficiency of intake structures with slopping channels. Two hydraulic factors, namely, the minimum to maximum wall pressure ratios (P_min/P_max) and the minimum V_r/V_z ratios (V_r/V_z)_min, were employed to differentiate between vortex flow and nonrotational flow. These two factors consistently led to the same conclusions under both subcritical and supercritical inflow conditions, indicating their validity and their potential application in the design and optimization of intake structures. The criteria of P_min/P_max > 0.2 and (V_r/V_z)_min > 0.2 can be used as criteria for the formation of stable vortex flow.

具有垂直落井的切向进水结构通常用于雨水和城市排水系统。涡流和切入流是在落井中观察到的两种典型的流动模式，其中前者由于其良好的排水性能和增强的安全性而成为理想的流动模式。这些流动模式之间的转变主要受结构设计和流量排放速率的影响。为了研究拦截性能以及涡流和切入流之间的过渡标准，进行了一系列数值模拟。通过比较各种情况下水面的演变、压力和速度分布以及旋流距离，分析了引道坡度、收缩率和流量的影响。具有 20 L/s 的较高流量，在收缩率低于0.4的落井和水平引水渠中观察到明显的积水现象。然而，在具有倾斜引水道的情况下，进水通道并不堵塞，这表明具有倾斜通道的取水建筑物的排水效率较高。两个水力因素，即最小与最大壁压比（P _min / P _max）和最小V _r /V _z比率（V _r /V _z）_min用于区分涡流和非旋转流。这两个因素在亚临界和超临界流入条件下始终得出相同的结论，表明它们的有效性及其在进气结构设计和优化中的潜在应用。P _min / P _max  > 0.2 且 ( V _r /V _z ) _min的标准 >0.2可作为稳定涡流形成的标准。