A SEMI-THEORETICAL APPROACH FOR DETECTION OF POSSIBLE CAVITATION AT DROPS IN DIVERGING CHANNELS

A sudden vertical drop may be constructed in a stilling basin when high variation in the land topography at the site of a control structure exists. The presence of the drop in the stilling basin affects the flow characteristics in the basin depending upon the incoming flow conditions, the basin geometry, position of the drop, height of the drop and the tailwater conditions. The effect of sudden drop on the hydraulic characteristics of submerged radial hydraulic jump was investigated under the assumption of hydrostatic pressure distribution on the sudden drop. It is believed that the pressure distribution on the sudden drop is less than the hydrostatic one and may be negative leading to cavitation problems under certain flow and boundary conditions. In this investigation, a simple semi-theoretical approach was developed to detect the possibility of occurrence of negative pressure at the sudden drops in radial stilling basins under submerged hydraulic jump conditions. The developed approach was based on the application of 1-D momentum and continuity equations. Experimental measurements were collected using laboratory flume to obtain realistic values of the coefficient of the pressure force on the drop. Wide range of flow conditions were tested at different positions of the drops in a radial stilling basin of constant angle of divergence. Significant effect of the drop position and drop height on reducing the pressure force on the drop was observed. The pressure on the drop was found to be less than the hydrostatic one when the drop is near to the sluice gate and may be negative at particular flow and boundary conditions and hence cavitation may be possible which could be detected using the present developed semi-theoretical approach