Three-Dimensional CFD Modeling for Optimization of Invert Trap Configuration to Be Used in Sewer Solids Management

Abstract

Flow field prediction and optimization of invert trap configuration have been carried out by using three-dimensional computational fluid dynamics (CFD) modeling with the help of FLUENT software using renormalization group (RNG) k-ϵ along with the discrete phase model (DPM). A hexagonal/tetrahedral shape and map-type nonuniform grid were chosen to discretize the entire computational domain, and a control volume finite difference method was used to solve the governing equations. In the present study, five different invert trap configurations (rectangular with and without lid on both sides, trapezoidal, trapezoidal with rectangular base, and rectangular with trapezoidal base with lid on both sides) have been simulated for the flow of three different inert sediment types (sand, styrocell, and plastic beads) at six flow rates (0.35, 0.70, 1.05, 1.35, 4.55, and 9.95 Lps) for each trap. The discharges selected in the present study cover the entire range of discharge expected in channels during dry weather flow and monsoon. The simulation results are capable of showing particle trajectories and the effect of flow rate and trap geometry on the flow patterns developed within the trap. Based on 3-D CFD modeling and experimental measurements, it has been concluded that the invert trap having a rectangular shape with trapezoidal base with lids on both sides is the most efficient trap configuration with highest sediment retention ratio.