Effect of Variation in Key Slope Ratios and Key Width Ratios on Energy Dissipation Over a Piano Key Weir

Piano key weirs (PKWs) are designed to efficiently regulate the discharge of water, particularly during high-flow events such as, floods. They are especially useful in managing water levels in areas prone to flooding.. The smaller footprint and longer crest length make this weir superior over the labyrinth and linear weir. Computation of energy dissipation to the weir is a vital flow feature, and its accurate estimation is essential while designing a weir. Currently, information and guidance are limited, with previous energy dissipation studies of PKWs. It is a key demand to assess the energy dissipation details over the PKWs. Therefore, the aim of present study was to investigate the energy dissipation over the type A trapezoidal piano key weir (TPKW) by varying the inlet-to-outlet key slope ratios (S_i/S_o) and key width ratios (W_i/W_o) of TPKW under subcritical free flow conditions. The results revealed that the dissipation of relative energy decreased with increasing S_i/S_o and W_i/W_o ratios, while the relative residual energy increased with increasing S_i/S_o and W_i/W_o ratios. Furthermore, the rate of energy dissipation at S_i/S_o = 0.60, 0.75, 0.80 was found to be 9%, 4%, and 2% higher, respectively, than at S_i/S_o = 1.00. However, for S_i/S_o = 1.25, 1.33, and 1.67, the rate of energy dissipation was found to be 4%, 7%, and 10% lesser, respectively, than at S_i/S_o = 1.00. Additionally, overall the rate of energy dissipation was found to be 57% and 43% at lower heads (h/P < 0.20) and higher heads (h/P > 0.20), respectively. The results also showed that the TPKW could dissipate the energy of flow by 60%, 54%, 50% and 47%, for W_i/W_o = 0.76, 1.00, 1.15, and 1.32, respectively. The model TPK1, having S_i/S_o = 0.60 with W_i/W_o = 0.76 was found to be hydraulically more efficient in energy dissipation than other tested models.