The effect of the upstream and downstream face slopes of the broad crested weirs on the flow characteristics

Broad-crested weirs are common engineering structures in irrigation systems and hydroelectric schemes. Varying the upstream and downstream face slopes are of the important factors affecting flow conditions and discharge efficiency of structure. In this paper, the Hydraulic Grade Line, free surface profile over the broad crested weir and separation zone at the upstream corner of it have been simulated by using Fluent software. The turbulence models considered are the standard and renormalization group (RNG). The simulation results are found in good agreement with measured data. The numerical simulations show that sloping the upstream face slope increases the discharge coefficient and decreases separation zone at the upstream corner and varying the downstream face slope does not affect the separation zone and discharge coefficient. Water depth before the critical depth in the weir with the steep upstream face slope however, is greater than the weir with the mild upstream face slope. The position of critical depth does not change by varying the downstream face slope. By using mild downstream face slope, negative pressure value decreases due to the decrease in curvature of streamlines, separation zone in downstream corner and the possibility of cavitations.