Flow Characteristics of a Drop Manhole with an Internal Hanging Baffle Wall in a Storm Drainage System: Numerical and Experimental Modeling

In urban drainage networks, manhole structures are used to dissipate energy and to decrease flow velocity, especially in steep slope areas. The purpose of this study is the numerical and experimental modeling of a new drop manhole in which an internal hanging baffle wall (IHBW) is used for increasing energy losses. Using open-source computational fluid dynamics (CFD) software called OpenFOAM, the proposed model is simulated numerically. Four types of regimes (R1–R4) are identified using impact parameters ($I_1$, $I_2$, and $I_3$) based on factors such as the jet impact point, the IHBW opening, and the pool depth. A semianalytical relationship is proposed based on the momentum equation to find the pool depth, which is in good agreement with the experimental data. By examining the coefficients of contraction and discharge, it was found that this system passes less discharge than an ordinary sluice gate due to the formation of a water curtain at the IHBW opening, but outperforms the existing rectangular drop manholes in terms of energy dissipation efficiency. It is mandatory to avoid the occurrence of Regime R4 in manhole design. For $I_1<0.9$ and $I_3<0.7$, lower and upper nappes may be submerged, which increases the possibility of manhole overflow and decreases energy dissipation efficiency. Numerical simulation results and laboratory observations are also in good agreement.