Experimental Investigation of The Flow Over an Arched Sharp-Crested Weir

Weirs are used to raise the water level in the open channels upstream of the weir for many purposes, such as irrigation; however, they cause turbulence and develop a hydraulic jump downstream of the weir. This leads to a process of scouring at the bed of the open channel, which threatens the stability of the weirs. An arched, sharp-crested weir is one of the weirs characterized by its ability to pass high discharges due to its long edge compared to the traditional sharp-crested weir. In this experimental study, four physical models of an arched sharp-crested weir were investigated with different ratios of the radius parallel to the flow (a) to the radius perpendicular to the flow (b) (1, 1.2, 1.4, and 1.6). The results displayed that the arched weir has a higher discharge coefficient (C_d) and energy dissipation ratio (η%) than the sharp-crested weir. In addition, increasing the (a/b) ratio led to an increase in (C_d) and a decrease in the turbulent length of the flow downstream of the weir, which significantly determines the length of the stilling basin. A secondary hydraulic jump was also observed in the arched weir, which provides additional energy dissipation. The discharge coefficient (C_d) ranges between 0.8 and 1.17 for different cases of arched weir ratios compared to 0.56 for a sharp-crested weir with the same dimensions and flow conditions. Regarding energy dissipation, it ranges between 56% and 69% for different models’ ratios (a/b), and for a certain model, it decreases as the water discharge increases.