Numerical Study of Suspended Solids Concentration in Drainage Pipes with Different Inflow Patterns

Abstract

The concentration change of fine suspended solids along a sewage pipe can be influenced by different water inflow patterns, which may cause water quality issues and affect the maintenance operation on sediment management. This study was conducted to explore the migration features of fine suspended solids under the influence of the variable inflow in drainage pipes. A three-dimensional numerical model was constructed to represent a more realistic flow condition and the interaction between water flow and suspended solids. Movement characteristics of fine suspended solids under different inflow conditions were numerically investigated based on the Euler–Lagrange method. The variations of the inflow pattern, particle vertical velocity, and concentration were discussed in detail to obtain the migration-deposition characteristics of fine suspended solids in a drainage pipe. The results show that, with the increase of flow velocity in steady inflow condition, the particles gradually diffuse to the bottom and the largest concentration of suspended solids gradually moves downward. For unsteady inflow condition, the flow change would lead to the change of sectional concentration and particle mass flow. The concentration of suspended solid in the front segment of pipe was more susceptible to the variable flow than the posterior segment. The highest particle concentration and mass flow situation can be influenced for the inflow pattern scenario with advanced flow peak, which means that the front section (at least half the length) is the important area where attention is required during sewer protection and pollution control processes. Besides, advanced flow peak of rainfall may cause more pollutants to accumulate in sewers.