Velocity Distribution and Separation Zone Characteristics in the Confluence of the Pipeline Network

The ability of urban pipe networks to transport water over time is significantly affected by the sedimentation of the pipe network, particularly at the pipe confluence area, where pollutants are frequently deposited and resuspended, leading to secondary pollution. In this paper, a 90° confluence pipe experiment (Dg=200 mm, Dt=100 mm, roughness is 0.014) is adopted, a detached eddy simulation (DES) model is used to simulate the turbulent flow field, and the comparison is made with the experimental data. The hydraulic characteristics of the confluence area and their relationship with the confluence angle and the confluence ratio are correctly investigated. Further comprehension of the flow field structure is made possible by the careful study of the confluence geometry and the investigation of the confluence generation mechanism. The results demonstrate that the convergence section of pipe network exhibits a variety of flow patterns, each with unique flow characteristics. These patterns include maximum velocity, reflux separation, deflection, high speed, stagnation, and flow recovery zone. The stagnation and recirculation zones steadily shrink from the surface to the bottom until they vanish in a longitudinal direction. The influx of tributaries exerts a more pronounced influence on the velocity distribution after confluence than before. The velocity magnitude downstream of the confluence is greater than that of the upstream section. The dimensions of the separation zone vary significantly with water depth. The shape of the junction changes with increasing water depth, becoming broader on one side and narrower on the other, while remaining the same length.