Determination of discharge coefficient in the tilted crown sharp-crested weirs

In this study, the performance of vertical and tilted crown weirs with different angles of the weir crest across the flow has been investigated using numerical and experimental models. Accordingly, various experiments are conducted on tilted crown sharp-crested weirs under different free-flow conditions. Moreover, computational fluid dynamic (CFD) modeling has been done using Fluent software to determine the best form of the discharge coefficient (Cd). In this study, the RNG model is used to define turbulence in the fluid flow and the two-phase volume of fluid (VOF) method is applied to define the interface of water-air in the flume. To verify the accuracy of the CFD model, the experimental data that was done in this research are used. Moreover, another goal of this research is to investigate the influence of the different angles of weir on hydraulic characteristics of flow such as pressure, velocity and Cd parameters. The results show that by increasing the weir crest angle across the flow (α), the Cd values are almost constant. Furthermore, the numerical results are in good agreement with the experimental models. As, the comparison of numerical and experimental data shows that the maximum absolute relative error (ARE) obtained are 2.8 %, which indicates the high accuracy of the CFD model. The vortex area with return velocity vectors can be seen in downstream of the weir and these vectors increase near the weir. In all velocity values, by decreasing the angle of weir to the flow direction, the Cd values increased and tends to a constant value while, the pressure values decreased. As for the velocity values in ranges of 0.05-0.23 m/s, the Cd value is ranged in 0.64-0.675. Finally, as the Reynolds and Froude number increase, the discharge coefficient decreases and tends to a constant number of 0.65 approximately.