Study of water head effects on discharge distribution and streamlines pattern over the asymmetric rectangular piano key weirs

In the present research, the flow over asymmetric rectangular Pianokey weirs with optimum geometrical ratio is modelled using experimental and numerical modeling. Effects of the water head on discharge distribution pattern over the weir crest is also studied. Effect of the relative height (P/Wu) is investigated on the efficiency of the Pianokey weir by changing the width of the unit key and keeping constant the weir height. The results showed that the weir efficiency increases by decreasing the relative weir height. Available analytical equations in the literature have been applied to compute the discharge passing over the hydraulically optimum weir and also the discharge coefficient for a given approach water head. Differences between the experimental and computed discharge coefficient values are considerable and thus the accuracy of the available equations is not sufficient. In this study, new equations have been developed to compute the discharge coefficient and discharge portions of the inlet key crest, outlet key crest and also the side crest of the asymmetric geometrically optimum Pianokey weirs against approach flow head. The consistency of the results of the new equations with experimental results is considerably higher than the results of available analytical equations in the literature.