Investigation of Improving the Flushing Vortex Flow Efficiency of Dam Reservoirs Outlet Gates

Investigation of Improving the Flushing Vortex Flow Efficiency of Dam Reservoirs Outlet Gates

Pressure flushing is a means of discharging sediments from reservoirs. Bottom outlets are among the main lateral structures of dams, which are used to control reservoir water pressure and discharge dam sediments. Due to the high flow rate and pressure drop, problems such as cavitation can affect these structures. The present research objective was to conduct a hydraulic analysis of the effect of the depth-to-width ratio of bottom outlets and increased efficiency of flushing through the escalation of eddy currents around the gate. This investigates the discharge characteristics of a bottom outlet with a moving gate by Computational fluid dynamics. This study also includes the effect of the height to width ratio of the conduit on aeration and flow field downstream of the gate. Changes are applied in three cases of constant height (depth) and variable width, constant width and variable height, and both variable height and width to make equal gate srea. Results indicated that more aeration while heightening and widening of the outlet. Also velocity increase and pressure decrease is observed while friction head is constant. The pressure drop is mainly caused by the increase in gate height by which transverse turbulence on water surface declines and decrease and the Vortex number increase. Therefore, the increase in reservoir gate height positively and significantly affects flushing and Sedimentation .It was possible to reduce pressure fluctuations and omit negative pressures by placing an air-entraining system after the bottom gate. In addition, the flow of air increases pressure relatively and decrease the risk of cavitation.