Three-Dimensional Numerical Study of Stacked Drop Manholes

Drop manhole structures are used in steep, sloped, urban areas to achieve an acceptable flow velocity inside the gravity network by reducing the slope in sewer pipes and dissipating energy. The energy dissipation is governed by manhole geometry, inflow conditions, and generated flow regimes. The experimental design parameters and the hydraulic performance of drop manholes have been extensively studied, whereas numerical studies are very limited. In this study, the authors have shown how the Flow-3D version 11.2 software package was used to onduct a three-dimensional (3D) computational fluid dynamic (CFD) simulation of rectangular stacked drop manholes (SDMs) to assess the impact of the geometric configuration and flow conditions on the energy dissipation efficiency. It was concluded that an economical cross section of an SDM is a ($3D\times 3D$) square, and that the total drop height should not exceed ($10D$) for one SDM unit, where ($D$) is the diameter of the inlet pipe. The maximum energy dissipation ranged from 78% to 90%, which was achieved when the first chamber’s drop height, ($H1$), ranged between 60% and 75% of the total SDM drop height, ($H$).