Influence Characteristics Of Hydraulic Variation On Pollutant Transport In Confluence Of Sewage Pipe Network

In the long-term operation of sewage pipe network,the deposition of suspended particles is an important factor affecting the transport capacity of pipe network,especially the most serious deposition after the pipe confluence.So this thesis with the convergence of sewage pipe as the research object,through the pilot experiments and computational fluid dynamics VOF coupling DPM three-dimensional numerical model research methods,the working condition of different velocity of the three convergence angles has carried on the modeling and numerical simulation,analyzed the research condition of hydraulic change and the trajectories of particles in the sewage pipe confluence,proved the influence law of the sewage pipe convergence flow change on the carbon,nitrogen,phosphorus typical pollutants migration characteristics,for the stable operation of the urban sewage pipe network system and provide the reference of water quality prediction and alleviate the urban water pollution has important engineering value and practical significance.The results show that different flow pattern zones are formed in the confluence section of the sewage pipe network,which can be divided into flow stagnation zone,large flow velocity zone,flow velocity deflection zone,reflux separation zone,maximum flow velocity zone and flow recovery zone according to the flow characteristics.In the direction of depth,the range of flow stagnation zone and reflux separation zone gradually decreases from the surface layer to the bottom layer and then disappears.Along the direction,the average vertical velocity of each section increases first and then decreases.The velocity distribution before the confluence is less affected by the inflow of the branch and the flow at the bottom of the main pipe is less affected by the inflow than that at the surface.Under the influence of the hydraulic conditions at the intersection of each working condition,the flow structures in different flow patterns are significantly different.On this basis,the transport of pollutants in the pipeline is further discussed.The particles in the before confluence and the flow recovery zone move smoothly with the water flow,and the settlement and suspension of TCOD,TN and TP are in a relative equilibrium.The movement of particulate around the flow velocity deflection zone fluctuates greatly under the influence of flow velocity and the pollutant is not easy to settle.The water flow stagnation area and the reflux separation zone are located at the junction of the confluence of the sewage pipeline,and the local flow pattern of the sewage changes.The settlement of particulate matter in this area is significant.Between the reflux separation zone and the maximum flow velocity zone,the velocity gradient of sewage varies greatly,the shear force of water flow dominates,and the suspended particles in the pipeline will constantly collide and friction,and most of the pollutants are suspended.The concentration of TCOD changes the most along the path,TN and TP are relatively small,and carbon pollutants are more likely to settle than nitrogen and phosphorus pollutants at low flow rate.It can be seen that the concentration distribution of pollutants is greatly affected by different confluence flow pattern zoning of sewage pipeline.