Numerical study of characteristics and discharge capacity of piano key weirs

A comprehensive numerical investigation was performed to better understand the flow patterns of Piano Key weirs (PKW) for different upstream heads, based on the volume-of-fluid model. The results of numerical simulation indicate that, the efficiency of side crests are limited by following factors: the change of side crest flow direction caused by the effect of the longitudinal flow velocity along the inlet keys, submerged flow regime in outlet keys, interference between nappes, and the head loss along the inlet keys, under the conditions of high upstream head, which eventually leads to the decrease in discharge efficiency with an increase in the upstream head. An orthogonal analysis revealed that, the weir height, inlet/outlet key width ratio, significantly affect the piano key weir discharge efficiency. New formulas with obvious physical significance and high accuracy for the piano key weir discharge were then derived and verified, which improve the accuracy of the design and structural optimization of the piano key weir.