The safety of hydraulic structures has social, economic, and environmental significance. To eliminate the damage induced by local scouring, either the scouring should be prevented entirely or the scouring depth should be minimized. This study numerically investigated the local scour that develops in the plunge pool downstream of high-head, classical contracted rectangular weirs operating under free overfall conditions. In the numerical analysis, a three-dimensional Reynolds-averaged Navier–Stokes (RANS) model with a standard k–ε turbulence closure was implemented in Flow-3D®. The analyses were conducted for three unit flow rates (q=0.15, 0.30, and 0.60 m3/s m) and three drop heights (H=0.25, 0.50, and 1.00 m) to determine the maximum scouring depth. Furthermore, the water jet velocity and impingement angle were analyzed. The experimental results were utilized to test the accuracy of the numerical model. For all cases, about 90 % of the equilibrium scour depth was reached within the first 15–20 min, consistent with previous studies. According to the results, the equilibrium scour depth increased from approximately 0.16 m to 0.23 m when the unit discharge was raised. However, after a specific value of the head height, the effect on the depth of scouring is slightly reduced due to the increased air entrainment entering the downstream pool. Computed jet impact velocities ranged from about 2.0 to 4.9 m/s, with impact angles increasing up to ~82° as the drop height increased. The results of the numerical model are generally compatible with experimental studies. This study is original in that it provides a three-dimensional CFD-based assessment of local scour downstream of high-head weirs under free overfall conditions and proposes a practical approach to estimate long-term equilibrium scour depth and jet impact characteristics.
İkincioğulları et al. (Fri,) studied this question.