Numerical Investigation on Effective Parameters on Hydraulic Flows in Chimney Proportional Weirs

Proportional weirs are of great importance in flow measurement due to providing the required accuracy in estimating the flow rate. In this study, the hydraulic parameters such as velocity distribution and velocity vectors, fluid pressure distribution in channel and weir, Froude number, stage-discharge diagram and discharge coefficient of chimney weirs with angles (The angle of triangular part of weir with the vertical wall) of 37˚, 42˚, 47.2˚ and 53˚ in the range of 2 to 9 liters per second was investigated using FLOW-3D software. In the present study, the RNG turbulence model was selected in comparison with the LES, k-ε and k-ω turbulence models due to low values ​​of relative error percentage and absolute error. The results showed that by increasing angle, at the same water head, the flow rate and Froude number decreases, and by increasing water head above the weir crest, the Froude number increases. Also, based on the results of numerical solution, by decreasing angle, the upstream mean velocity increases. In this study, based on dimensionless parameters, a nonlinear polynomial equation was obtained by combining the data of all modeled weirs to predict the discharge coefficient. Comparing the results of experimental and numerical solution with the presented equation indicates the high accuracy of the presented equation.