Experimental study of Discharge Coefficient in Two-Cycle Piano Key Weirs

The piano key weir is a developed version of nonlinear weirs with a very high discharge capacity. Due to the increase in effective length and consequently the increase in drainage efficiency of these weirs, they can be used in dam spillways or water regulation structures. This study aimed at the investigation of two-cycle piano key weir with a triangular nose. Several experiments have been conducted to determine the effect of geometric parameters of the input-to-output key widths (Wi/Wo( and the ratio of the weir’s length to the length of downstream slope (B/Bi) on the discharge coefficient. The results of this study showed that with increasing hydraulic load, the discharge coefficient was first increased and then reduced, and by increasing the input-to-output width ratios from 0.8 to 1.25, the discharge coefficient of piano key weir increased up to 26 percent. Using triangular nose has a positive effect on the discharge coefficient. In addition, the comparison with the results of other researchers showed that have the relationship developed in this study has less error than other relationships.