RICRI Research Seminar: Climate-Resilient Vortex Dropshaft Design: Mitigating Urban Flood Risks by Controlling Flow Regime Transitions under Extreme Rainfall

Climate change-induced extreme rainfall events pose unprecedented challenges to urban drainage systems, making the hydraulic performance optimisation of drop shaft in drainage structures critically important for effective stormwater management. The flow regime transition mechanisms between plunging and vortex flows in drop shafts with tangential intakes are investigated using an integrated approach combining 3D numerical simulations, physical experiments, and analytical solutions. Five distinct flow regimes are identified: weak drop flow, moderate drop with weak rotation, strong drop with moderate rotation, partial blockage with strong rotation, and severe blockage. Comprehensive criteria are developed for flow regime identification: pressure ratio criterion, velocity ratio criterion, and dimensionless drop height criterion. The findings provide practical design guidelines for optimising drop shaft performance in urban drainage systems capable of managing climate change-driven extreme rainfall, with the proposed criteria enabling real-time monitoring and operational control of flow regimes during intense storm events.