Experimental investigation and CFD modelling of flow, sedimentation, and solids separation in a combined sewer detention tank

The lack of knowledge about particle behavior in combined sewer detention tanks remains a significant difficulty for the design of these works. In this paper, the use of 3D computational fluid dynamics (CFD) is investigated for studying flow, sedimentation, and solids separation in a tank equipped with one inlet pipe and two outlets (outlet pipe and overflow weir). Twenty-three experiments have been carried out. The Fluent^® CFD code is used for simulating the flow field. Sedimentation and solids separation are calculated using the particle tracking facility of the software. Bed shear stress (BSS) and bed turbulent kinetic energy (BTKE) boundary conditions are investigated. The time scale constant of the random walk model has been set to the unexpected value of 0.5-1. The simulated mass percentages and deposit locations are in good agreement with measurements. The sensitivity to the BTKE threshold and particle density is studied.