The effect of the inlet/outlet width ratio on the discharge of piano key weirs

A piano key weir (PKW) is a solution for improving the efficiency and safety of reservoirs and simplifying their management. To investigate the influence of the inlet/outlet width ratio Wi/Wo on the discharge efficiency of PKWs, a three-dimensional numerical model based on a standard k−ε turbulence model and volume-of-fluid (VOF) method is employed, and the flow characteristics of nine laboratory-scale PKWs with different Wi/Wo ratios are studied numerically. The results confirm that PKW configurations with Wi/Wo>1 are generally superior to those with Wi/Wo<1 in terms of discharge capacity. However, as the water head rises, the discharge efficiency of the PKW with a greater Wi/Wo decreases more rapidly. By decomposing the total discharge into inlet, lateral and outlet components, according to the flow features of each overflow crest and their contributions to the total discharge, the intrinsic influencing mechanism of Wi/Wo on the discharge performance of PKWs is revealed.