Experimental study on the effect of number of cycles on the hydraulics of trapezoidal piano key side weirs

Recently pianokey weirs become important in hydraulic structures. In this paper effect of the number of cycles on the flow of pianokey sideweir has been investigated experimentally. 45 experiments on single, two, four, six cycles pianokey and sharp crest linear weir on different heads (H/P = 0.3, 0.5, 0.65, 0.85 and 1) has been conducted. The input flow rate to the main channel was applied in such a way that the flow in this channel became subcritical. Experiments are conducted for different heads in order to determine the surface water profile and discharge coefficient. At the beginning of the opening, the height of water decrease significantly and as the number of cycles increases, this decrease further so that in 6 cycle water reduction is 5 percent more than 1 cycle. Discharge coefficient of the weir decreases with increasing the number of cycles in a constant effective length of the weir from 5 to 21 percentages. The ratio of discharge coefficient of the TPKWs to the rectangular sharp crest weir, was between 1.15 and 1.75. Experimental results show that the discharge coefficient of inertial weirs are larger than inverted ones but this difference is not significant.