Discharge coefficient of side spillway rectangular weir in a dissipating energy sewage manhole

Sewage flow dissipating energy manholes play influencing role in reducing flow velocity with minimizing manhole erosion and gas emission. The current study is focusing on determining the discharge coefficient value for a side spillway rectangular weir situated longitudinally in a sewage dissipating energy manhole. The manhole receives pressurized flow through incoming force main and discharges water under gravity through outgoing pipe. The direction of flow alters 90 degrees two times within the manhole; after entering the manhole within inlet submerged channel, and before exiting the manhole within outlet channel. Between those alterations flow passes over the weir. Flow conditions was simulated using Computational Fluid Dynamics (CFD). Using the volume of fluid method (VOF), the free surface flow over the weir was modelled to track flow characteristics at subcritical flow conditions. Five different cases for weir length and three different cases for weir height were considered. The value of the coefficient was found to range from 0.32 to 0.57. It increases as the length of the weir decreased.