Experimental study of flow over piano key weirs with different plan shapes

The piano key weir (PKW) is an evolution with more hydraulic efficiency, compared to labyrinth weir. The studies on this type of weir have shown a significant increase in its discharge efficiency, especially at low heads. In this study, discharge coefficient of various shapes of piano key weir (i.e. rectangular, trapezoidal, and triangular) is investigated experimentally. Also, the aeration process of the studied weirs is described. According to the results, it was found that the discharge coefficient of the triangular PKW is about 28.2% more than the discharge coefficient of the rectangular PKW, and the discharge coefficient of the trapezoidal PKW is about 12.9% more than the discharge coefficient of the rectangular PKW. Also, the discharge capacity of the rectangular, triangular, and trapezoidal PKWs are 3.8, 3.96, and 3.96 times the sharp crest weir, respectively. The equations introduced for the discharge coefficient show good agreement (with R2 from 0.968 to 0.988 and average percentage error from 0.82 to 2.6%) between the actual and calculated values.