Experimental Study of Hydraulic Flow of Circular Piano-Key Inlet in Shaft Spillways

One of the most important conflicts that shaft spillways have to deal with is vortex formation. This phenomenon leads to some unfavorable effects such as vibration in the body of structures, air entrainment and reduced overflow capacity of the spillway. Among all solutions for disrupted vortex formation, an innovative one called circular piano-key spillway, based upon piano key weir principles has not been noticed as well as other solutions. Hence, in this study, experiments were conducted on circular piano-key spillway models. Results showed that in a constant head, the greater amounts of discharge have been measured for circular piano key inlet with an angle of 90 degrees. Comparison between discharge coefficients of three circular piano key inlet models showed that for a constant amount of H/D (Head/Diameter), circular piano key inlet with an angle of 90, 60 and 45 degrees have the greater amount of discharge coefficients, respectively. Experiment results indicated that circular piano-key spillway (with an angle of 90 degrees) increases overflow discharge capacity about 15.16% compared with shaft spillway. Among circular piano key inlets, the model with an angle of 90 degrees has the best hydraulic performance.