Abstract
The high velocity flow of water along with the severe head loss causes several turbulences and may lead to occurrence of cavitation phenomenon in hydraulic structures and severe destruction in some parts of them. Flow separation within the slots make eddies and vortices, which can also create cavitation. This study deals with the pressure fluctuations which are product of current severe turbulence, their processes and cavitation phenomenon at the gate slot region (with length/wide ratios of 2 and a 45o angle to the edge of the vertical-gate) of physical model of bottom outlet of Gotvand Olya storage dam. The study was conducted at the gate openings of 10, 30, 50, 70, and 100% and in different 2, 3 and 4 meter-heads and at0.1 %probability levels. Data collected using a transducer, were then transferred to an amplifier, and finally recorded in a computer. The results obtained indicated that at the gate openings of 30%, 50% and 70%, risk of cavitation occurrence is the maximum and at 10% and 100% it is the minimum. Also the piezometer, closest to the gate edge, is subjected to more fluctuations and critical point of pressure fluctuations are transferred to higher points upon with increase of gate opening. Coefficient of pressure fluctuations (C\'p) is the maximum at10 % opening that indicates compaction and pressure beats to the structure in this opening. Therefore control hydraulic conditions and geometric changes of the gate slot decreasing cavitation occurrence to the minimum would be possible. Keywords: Bottom outlet, Cavitation, Coefficient of pressure fluctuations, Gate slot
Highlights
Pressure fluctuations and cavitation phenomenon on the bottom outlet of this dam at the service gate slot have been investigated
Gotvand Olya dam is located on Karoun river in 35th km of Shoushtar Town
Under conditions of high velocity flow cavitation can occur within gate slots (Jack Lewin, 2001)
Summary
Pressure fluctuations and cavitation phenomenon on the bottom outlet of this dam at the service gate slot have been investigated. The coefficients of pressure fluctuations including C'p, C'p+, C'p- and Cp as well as cavitation index were calculated and investigated and analyzed. Investigation and necessity of conducting this research in this relation is so important because pressure fluctuations followed by cavitation phenomenon have so far led to serious damages in most parts of hydraulic structures including the tunnel of bottom outlets of dams and have caused serious complications to structure performance and have sometimes interrupted it.
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