Investigating the discharge characteristics over a piano key weir with varying key slope and key width ratios under varying discharges

Abstract The objective of the present study was to investigate the effect of inlet to outlet key slope ratios ( S i / S o ), inlet to outlet key width ratios ( W i / W o ) and head over the weir on the coefficient of discharge ( C pkw ) of type-A trapezoidal piano key weir (TPKW). It was observed that the C pkw of TPKW was found to be decreased as the S i / S o ratio reduced. The percentage of reduction in C pkw was found to be 18.5%, 16%, 13.7%, 9.4%, 6.3%, and 3% at S i / S o = 0.60, 0.75, 0.80, 1.00, 1.25, and 1.33, respectively in comparison with the S i /S o = 1.67. As far as the effect of W i / W o ratio on the C pkw of TPKW is concerned, the C pkw of TPKW was observed to be increased with increasing W i / W o ratios. Moreover, the C pkw at W i / W o = 1.32 and W i / W o = 1.15 was found to be 9.4% and 7.5% higher than W i / W o =1 respectively, while for the case of W i / W o = 0.76, its value was found to be 3.3% lower than W i / W o = 1. Furthermore, the hydraulic efficiency of TPKW was found to be decreased as head over the weir increased. The maximum value of C pkw of TPKW was observed to be 3.2 corresponding to lowest h / P ratio for the model having S i / S o = 1.67 and W i / W o = 1.32, while the minimum value of C pkw of TPKW was found to be 1.58 corresponding to highest h / P ratio for the model having S i / S o = 0.60 and W i / W o = 0.76. Additionally, sensitivity analysis results revealed that the C pkw of TPKW is more sensitive with h/P ratio than other ratios.