The Effectof Different Openings of Lift Bottom Outlet Gates of Dams on theOccurrence of Cavitation Phenomenon

High velocity of fluid along with the severe head loss causes several turbulences in the flow and may lead to the occurrence of cavitation phenomenon in hydraulicstructuresand severe destructions in some parts of them. In this paper، pressure fluctuations، which are a product of severe turbulences، their processes and cavitation phenomenon in the service gate slot zone of physical models of bottom outlets of the Karoun4 and theGotvand-e Olya Dams was investigated. Theratioof length towidth ofthe slot1. 75 and 2 and in 10،30،50،70 and %100 openings and in different 2، 3 and 4 meter-heads، and is based %0. 1 probability levels had been investigated and compared. The results obtained indicated that in the30، 50، and %70 gate openings، cavitation index is the minimum، and in %10 and %100itis the maximum. Also، the piezometer،which is closer to the gate edge، is subject to more fluctuations، and the critical point of pressure fluctuations are transferred to the higher points with anincrease in gate opening. Dimensionless coefficient of pressure fluctuations (C''p) with ratio1. 75، in %30 opening and ratio of 2، in%10 opening is the maximum that indicates compaction and pressure beats to the structure at this openings.