Modeling Transient Mixed Flows in Drainage Networks With Smoothed Particle Hydrodynamics

Transitions between free-surface and pressurized flows (transient mixed flows) are common and complex phenomena in urban drainage systems. Currently, the free-surface-pressurized flow models are mainly solved by grid-based numerical schemes, while the application of meshless methods to such problems remains relatively unexplored. Therefore, this study proposes a novel meshless model based on Smoothed Particle Hydrodynamics coupled with the Two-component Pressure Approach (SPH-TPA) to simulate transient mixed flows. To extend the applicability of the SPH-TPA model to drainage networks, a junction boundary model is developed based on the flow regimes in the junction and inflowing/outflowing pipes. Three idealized cases and two experimental cases are investigated for model validation and parameter sensitivity analysis. The results indicate the capability of the SPH-TPA model to deal with various flow conditions and capture transition interfaces accurately. Furthermore, a hypothetical drainage network is applied to evaluate the performance of the SPH-TPA model for simulating mixed flows in complex drainage systems, and the results of the SPH-TPA model demonstrate better accuracy and stability compared to the SWMM (Storm Water Management Model). The proposed SPH-TPA model provides an alternative tool to investigate transient mixed flows in urban drainage systems.