Numerical analysis of local scour occurring on downstream bed by free overfall weir

Aside from the fact that a building is economical or ergonomic, the most important issue that civil engineers focus on is structure security. The weirs used in water engineering are also important hydraulic structures that provide the flow of water from upstream to downstream. These jets, which can be designed as free overfall, can affect the security of the structure. For this reason, minimizing the local scour that may occur in the downstream pool is a must for the safety of the structure. In this study; rectangular, triangular, trapezoidal and labyrinth weirs for free overfall were analyzed numerically with the Computational Fluid Dynamics (CFD) method to estimate local scour depths. In the numerical modeling of this study, Flow3D which is successful software for solving problems such as open channel flow, sediment transport and scouring was used. As the turbulence model, k-ɛ turbulence model which is frequently used in the literature was used. For the classical rectangular weirs used in the study, 13 analyses were conducted using three different discharges (15, 20 and 30 L/s), three different drop heights (0.25, 0.50 and 1.00 m) and two different tailwater depths (0.25 and 0.50 cm). The classical triangular weirs were designed with 90° angle and 8 analyses were conducted using two different flow rates (15 and 30 L/s), two different drop height (0.50 and 1.00 m) and two different tailwaters (0.25 and 0.50 m). For classical trapezoid weirs, 7 analyses were conducted using two different flow rates (15 and 30 L/s), two different drop height (0.50 and 1.00 m) and two different tailwaters (0.25 and 0.50 m). The labyrinth weir is designed as a double-eyed trapezoid using two different sidewall angles (=22 and 30º). 8 analyses were conducted using two different flow rates (10 and 30 L/s), two different drop heights (0.25 and 0.50 m) and two different tailwater depths (0.25 and 0.50 m) for the labyrinth trapezoid weirs. The results of the CFD analysis were compared with the experimental results. The graphs, tables and simulation results of the analysis results were interpreted. In addition to these, it is aimed to make a contribution to the literature by comparing the results of the analysis carried out by using different weir types. In comparing the results of 35 analyzes carried out within the scope of this study with experimental results; the relative error rate is less than 20%. This value is acceptable for sediment problems. The local scour at downstream of labyrinth weir is less than the local scour at downstream of the classical weirs. However, the horizontal distance of maximum scour depth for labyrinth weir is less than the classical ones.