Experimental Study on the Discharge Coefficient of Triangular Piano Key Side Weirs with Different Geometries

The piano key side weir is introduced as a new hydraulic structure to improve the outflow performance where the opening length of distribution channels is restricted. This study used 370 high-resolution tests on three linear and 24 triangular piano key side weirs. The study experimentally investigates the effects of different upstream angles on the discharge coefficient of the triangular piano key side weirs with various geometries. In these tests, continuous improvement has been achieved by reducing the ratio of upstream angles for triangular piano key side weirs with the same crest length. The estimation of discharge coefficients using De Marchi’s equation shows an average increase of 7.2% to 17% for the triangular piano key side weirs, considering the variation of upstream angles. The data analysis shows that the deflection angles of triangular piano key side weirs are also vital for outflow efficiency. A new reliable equation is proposed to estimate the discharge coefficient of piano key side weirs based on some dimensionless parameters (different ratios of upstream angles (δ1/δ2), dimensionless weir length (L/W), dimensionless weir height (h1/P), dimensionless overhang length (h1/ Bi), and the downstream Froude number (F2). Also, the statistical indices were used to evaluate the precision of the nonlinear equation for triangular piano key side weirs. The R2 and MAE for 70% of the experimental data were 0.91 and 0.052, respectively.