Introduction of Oblique Cylindrical Weir as an Effective Approach to Increase the Discharge Coefficient

Cylindrical weir is one of the hydraulic structures that was used to measure flow rate and control flood, and is less expensive than similar structures. In this study, the numerical model validation is performed with an accredited experimental model in three different diameters (11, 9 and 6.35 cm), and in three different angles (45, 90 and 135 degree) toward the wall with Flow-3D software. According to the simulation, in the results with k-ε turbulence model there is a good adaptation than the other turbulence models such as the RNG and LES model, and the correlation coefficient (R2=0.965), indicated that the k-ε turbulence model is the best. Due to an increasing the length of weir in oblique position and changing the situation of spillway from direct position to oblique position, discharge coefficient will increase, so leads to increasing of discharge. The results show that in models with complementary angles, because of the similarity of these models in the flow pattern, the discharge coefficients will be almost equal to each other. With increasing the diameters of spillway from 6.35 cm to 11 cm, discharge coefficient reduced up to 50%. Maximum of the correlation coefficient between discharge and discharge coefficient for cylinder with 11 cm diameter is equal to 0.95 that show high effectiveness of discharge on discharge coefficient.