Comparison of the effect of the input to output key width and slope of key on discharge coefficient in two-cycle and three-cycle Piano Key Weirs with a triangular nose*

The Piano key weirs are new types of weirs which have a high discharge capacity and are more economical and highly efficient.in the current study, to determine the effects of geometrical parameters of ratio of input key on discharge coefficient,180 experiments have been done on two-cycle and three-cycle weirs under different hydraulic conditions. The results of the study indicated that by increasing hydraulic load, at first discharge coefficient increases and then it decreases. Discharge coefficient in the piano key weir also increases to 26% by increasing ratio of input key to output key from 0.8 to 1.25.the analysis of number of cycles revealed that the maximum rate of discharge coefficient for two-cycle weir was between 0.6 and 0.76 and for three-cycle weir was between 0.4 and 0.59.throuout the whole process, the performance of two-cycle weir was much better than three-cycle weir since the discharge coefficient of it was 29%.the reasons for this are the complexity of discharge conditions in three-cycle weir, more streamlines interference, local immersion , more energy loss and the increasing number of cycles in a specified width with the same effective length. The optimum condition of A-type piano key weir in terms of the simultaneous effect of weir slope and ratio of input width to its output using triangular nose has been examined. The analysis of findings showed that a piano key weir with a ratio of key width of 1.25 and a slope of 25.2% with a triangular nose is the best combination for the maximum rate of discharge coefficient.