An Investigation of Cavitation Index of Dam Bottom Outlets with a Sluice Gate

The main causes of damage in hydraulic structures are cavitation, vibration, and crushing. Cavitation, a phenomenon that occurs at high velocities, can damage hydraulic structures. It occurs when the pressure of the water flow drops below its vapor pressure. Flow aeration in hydraulic structures is known to reduce cavitation damage. Bottom outlet aeration is one example of this. The high-velocity flow in the bottom outlet is a mixture of air and water. This airflow results from the sub-atmospheric pressure downstream of the gate. The air vent supplies the air entrained by the high-velocity flow. Without a sufficient air supply, the pressure drop downstream of the gate will cause cavitation. This study investigates the cavitation index of bottom outlets with a sluice gate and three different outlet cross-sections. The results indicate that the cavitation index decreases with an increasing Froude number. The geometry of the bottom outlet cross-section did not significantly affect the cavitation index. An equation is also presented that relates the cavitation index to the Froude number, the gate opening rate, and the ratio of the hydraulic radius to the bottom outlet length.