Numerical Investigation on the Evaluation of the Sediment Retention Efficiency of Invert Traps in an Open Rectangular Combined Sewer Channel

Uncontrolled municipal solid waste, construction waste, and sediments from streams release fine sediments into sewer and urban drainage systems. Sediment transportation and deposition in sewers and urban drainage channels are major issues faced by nations across the globe. Earlier investigations on the invert trap mainly focused on varying the flow depth, particle size, and slot opening. There are limited studies available on different invert trap geometries, which play an important role in sediment trapping. The present study focuses on invert traps with varying the geometry setup with a base geometry (top width as 32 cm, depth as 28 cm) of a rectangular chamber with a trapezoidal base (BG). The changes considered include an arc passing through three points (G1), an isosceles triangle (G2), and a right triangle (G3) for different slot openings (9 and 15 cm) and flow depths (2, 3, 4, and 5 cm) for natural sewer solids (NSS1). In the current study, two-dimensional (2D) computational fluid dynamics (CFD) modeling was performed using volume of fluid (VOF) and discrete phase model (DPM) along with a realizable k-ϵ turbulence model in fluent software for flow field simulation and retention efficiency in the considered geometries. Flow depth, slot opening, and the geometry of the invert trap are parameters that affect trap efficiency. The investigation shows that the 2D CFD VOF-DPM model predicts better trap efficiency for NSS1 with particle size (diameter ranges 0.15-0.30 mm) when compared with Mohsin and Kaushal's experimental data. In all the considered geometries, the right triangle (G3) was observed to have the maximum trap efficiency for both the slot openings and any given flow depth.