Experimental study of cavitation index in an ogee spillway by considering convergence angle of sidewalls

Cavitation is among the most complex and common damages occurring in spillway structures, which is one of the most expensive parts of a dam. The cavitation index, as the one of the most efficient approaches, can be used to analyze this important hydraulic phenomenon. The present study examines the changes in the cavitation index caused by changes in the convergence angle of an ogee spillway's sidewalls with an arc in the plan. To this end, a spillway was constructed on the 1:50 scale. Then, it was tested with four different convergence angles, including 0 degrees, 60 degrees, 90 degrees, and 120 degrees, relative to the spillway's sidewalls and six different flow rates per unit width ranging from 6.74 to 48.42 (I/s)/m. The results indicated that as the flow rate increased, the cavitation index relatively declined at both crest and chute of the spillway while growing at its toe. It was observed that the lowest cavitation index was found to be 1.54 in.X/H-d = 2.42 at an angle of 0 degrees and a flow rate per unit width of 40.52 (L/s)/m.