Investigation on Discharge Coefficient of Circular Crested Weir using Numerical Modeling

Cylindrical overflows and circular crested weirs, due to economical reasons and simplicity of manufacture, compared to other overflows can be used in measuring flow intensity, discharge and water level control in channels and reservoirs. In this study, flow characteristics in 28 physical models of circular crested weirs using the FLUENT model were simulated and the results were compared with the physical models. In addition, the effect of the radius, height, upstream slope, downstream slope and upstream arc crest overflow parameters were also investigated. Simulation in FLUENT software was made by using k-Ɛ turbulence model and VOF multiphase model. Comparison of simulation and experimental models indicated that NRMSE is 7.7% and the relative error equals to 6.4%, which indicates the accuracy of numerical modeling in calculation of discharge coefficient. As a result, good agreement was obtained between FLUENT model and physical models. The results also showed that discharge coefficient increases by the total load (H1/R), equal to the values of 2, 1.3 and 0.96 in cylindrical overflows, semi cylindrical and quadrant cylindrical respectively. Increasing the weir height also causes increase in the discharge coefficient. Other parameters have slight impact on the discharge coefficient. Moreover, discharge coefficient of cylindrical weir has the maximum (Cd=0.915) and the quadrant cylindrical weir has the minimum value (Cd=0.851) under constant H1/R.