Experimental investigations and three-dimensional computational fluid dynamics modeling of sediment transport in tanks influenced by cavities

Abstract

Sediment transport is a very complex process in urban water systems, and sediment movement mechanisms are poorly understood. However, it is necessary to comprehend sediment transport to optimize stormwater and sewer tank designs for better performance in trapping particulate pollutants. This work focuses on the numerical simulation and experimental investigation of tank sediment transport. In the numerical simulation, a discrete phase model is applied to calculate particle trajectories, and the particle tracking calculation is coupled with the steady-state flow calculation. A user-defined function is developed in the Fluent computational fluid dynamics (CFD) code to implement the settling condition and improve the particle motion predictions. In the experimental work, a back-scattered ultrasonic method is used to measure the velocity field, and the accumulation of particles at the bottom is reproduced by transforming the raw experimental data. The sediment deposition is also recorded photographically, and the trap efficiency is calculated. The CFD and experimental results are compared to estimate the accuracy of the modified settling boundary condition, showing an improvement in the trap efficiency and deposition zone predictions. High water level in the tank corresponds to higher sediment trap efficiency, and sediment deposition type is strongly affected by the water level. Tank length and the presence of cavity alter the sediment deposition zone, and the presence of cavity increases the trap efficiency of tank.