Study of Flow Hydraulics in Expansive Gradual Transitions Open Channels

Channel expansions are common in both natural and artificial open channels. With increasing cross-sectional dimensions in an expansion, the flow decelerates. Under Subcritical flow and steady flow conditions, reducing the flow velocity due to increasing the water pressure and adverse pressure gradient. In this study, the flow hydraulic along the expansive transition of rectangular to trapezoidal under subcritical flow has been investigated experimentally. Also, a three- dimensional numerical simulation of the flow pattern was developed using the fluent software with RSM turbulent model. Water surface and flow velocity profiles at different sections of transition were compared with experimental results. The results showed a good agreement between numerical and experimental results. Then, the efficiency of the transition and coefficient of energy head loss were calculated. The results show that with increasing the upstream Froude number, the efficiency of the transition and coefficient of energy head loss are decreased and increased, respectively. After calibration, the effect of inflow Froude numbers on flow separation zones, secondary currents, and bed shear stress along the transition was investigated numerically.