Influence of auxiliary geometric parameters on discharge capacity of piano key weirs

Abstract A piano key weir (PKW) is a new type of labyrinth weir that has the advantages of a high discharge capacity, little affected by terrain restrictions, cost-effectiveness, and wide applicability. It is an efficient type of spillway from the hydraulic and economic viewpoints. To elucidate the effects of the auxiliary geometrical parameters of the PKW, i.e., the nose and the parapet walls, on the discharge capacity, six different PKW models were tested in a rectangular tempered glass flume with a length of 16 m, a width of 0.5 m, and a depth of 0.75 m. The experimental results indicated that adding a triangular or rounded nose improved the flow patterns, and increased the discharge capacity of the PKW by up to 8.5% with a relative water head of 0.188. Furthermore, the addition of a parapet improved the discharge capacity of the PKW, and a higher parapet wall yielded a higher discharge efficiency. When the nose form and the height of the parapet wall were optimized comprehensively, the total discharge of the PKW was increased by up to 16.8%. The study reveals the influence mechanism of the nose form and the parapet wall on the discharge efficiency of the PKW and provides a reference for the geometric design and engineering application of the PKW.