Cavitation Study in Bottom Outlet Gate Slots by Pressure Fluctuation

Around the high head gates as the velocity is too high, every non uniform object such as a slot makes the flow too disturbed. Vertical-lift gate required recessed slots in abutments for the movement of the gate slides. The flow of water across the slots causes flow separation at the upstream lip of the slot and reattachment on the downstream side. Eddies are set up within the slots and vortices are formed. Thus, under higher velocity flow conditions (due to high head), cavitations can occur within gate slots by fluctuations. In addition of cavitations the pressure fluctuation can make impacts on the structure too. This hydraulic phenomenon can be occurred with serious damages. In this research, experimental data is used based on measuring pressure fluctuation by pressure transducer under an experimental model which has built and taken place in Michelle Hydraulics Laboratory at civil engineering department of the University of Melbourne. Pressure fluctuations were measured under two group of seven piezometers along the two gate slots for gate positions of 10%-10%, 30%-10%, 50%-10%, 70%-10%, 30%-30%, 50%-30%, 70%-30%, 50%- 50%, 70%-50%, 70%-70%, head condition behind the gates were constant for all tests. The results were analyzed and presented as Cavitations Index in two slots. The cavitation indexes were calculated in based 0.1% probability levels of fluctuation pressures. Other probability levels contained 1%, 5% as higher pressures and 95, 99 and 99.9% as higher pressures, were studied in this paper.