Study of Pressure Fluctuations and Probability of Cavitation Occurrence in the Slot of Bottom Outlet Gate of Gotvand Dam

High velocity of fluid along with the severe head loss causing several turbulences in the flow، may lead to the occurrence of cavitation phenomenon in hydraulic structures and severe destruction in some parts of them. In this research، pressure fluctuations، its processes and cavitation phenomenon in area of service gate slot have been investigated and analyzed by a hydraulic model including bottom outlet of Gotvand Olya storage dam. These experiments were conducted at the gate openings of 10، 30، 50، 70، and 100 percent and at different 2، 3 and 4 meter-heads in the region of gate slot. Pressure data were collected by using a transducer and were then transferred to an amplifier and finally were recorded in the computer. These data were analyzed on the basis of 0. 001 probability level. The obtained results indicated that the probability of cavitation occurrence in 30، 50 and 70 percent of gate openings was higher than 10 and 100 percent ones. Also the piezometer which was the closest to the gate lip was subject to more fluctuations and critical point of pressure fluctuations was shifted to higher points due to increase of gate opening. ِِDimensionless coefficient of pressure fluctuations (C''p) was the maximum for 10 of gate opening، indicating compaction and pressure impacts on the structure in this opening. So by suitable lining، control of hydraulic conditions، and change of slot geometry probability of cavitation occurrence can be decreased to the lowest value.