Experimental and Numerical Flow Modeling in Drop Manholes
Mohammad Reza Chamani
Mohammad Karim Beirami
Pipe outlet structure
Nowadays, the catchment areas of impermeable surfaces increase due to urban development and construction of various buildings on permeable soils. It increases the volume and intensity of runoff. Consequently, the capacities of existing drainage systems for flood control are inadequate and their designs should be modified, accordingly. In drainage systems of urban runoff, water channels have little slopes to control the velocity of flow. Drop manholes are usually provided to offset the elevation differences between the channel slope and the ground slope. They are used to reduce the energy as well. The aim of this thesis is to investigate the performance of drop manholes to increase the energy loss and the flow discharge. The scheme combines drop manhole and pipe outlet structure. Pipe outlet structure usually consists of hanging baffle and end sill. A physical model of drop manhole was constructed in the Hydraulics Lab, Isfahan University of Technology (IUT), Isfahan, Iran. It consisted of an upstream pipe with length of 2 m and diameter of 0.19 m, a drop of 0.345 m height, and a rectangular channel with length of 2.5 m and width of 0.40 m. A hanging baffle was installed after the drop. To generate a free surface flow, a Jet Box was used upstream the drop with two nominal opening ratios of 50 and 80%. Discharge ranged from 10 to 38 L/s and the Froude number was between 1 and 4. Different flow regimes and hydraulic characteristics of flow were investigated. Using OpenFOAM, an open-source software, the flow was simulated numerically. To verify the results, the first set of experiment was conducted on a model without hanging baffle and the experimental and analytical results were compared with those of the existing rectangular vertical drops. In the second phase of experiments, a model with hanging baffle is used.