Investigation of Cavitation at the Roughened Bed of Abrupt Drop Stilling Basin

Investigation of the possibility of cavitations at the bed of an abrupt drop roughened bed stilling basin was conducted by means of a physical model and measuring the instantaneous pressure fluctuations. The tests were conducted under different Froude numbers ranged between 2.98 to 11.81 and discharges between 38 to 230 liters per second. The pressure fluctuations were measured at the basin centerline and two other lines on both left and right of the centerline. The statistical analysis of pressure fluctuations including calculation of maximum, average and minimum values at any period of time (90 seconds) was also made. The total number of piezometers was 109 and for each piezometer a total number of 3562 data were available for the above mentioned time period. The analysis of results showed that the least amount of pressure or even negative pressure had been recorded on those piezometers which were located at the direct impact of the incoming jet. Therefore, at these piezometers, the possibility of occurrence of cavitations was investigated by calculation of cavitation index. The computed values of cavitations indices show that all these values are greater than 2.78 and therefore there is no threat for cavitations occurrence.