Computational fluid dynamics modeling of flow characteristics over V-notch side weirs

Abstract

Side weirs are one of the most important and applicable hydraulic structures for water control and diversion systems that require careful review and accurate design due to their critical importance. In this study, flow characteristic over a V-notch side weir in a rectangular channel was carried out experimentally. Simulation was also carried out using Computational Fluid Dynamic (CFD) to describe the discharge coefficient (C_d). A relationship between discharge coefficient (C_d), Froude number (Fr) and Reynolds number (Re) were established with dimensional analysis and their linear and multiple regression models were fitted using Statistical Package for the Social Sciences (SPSS)for correlation test at 95% confidence. Simulation of flow was carried out using COMSOL Multiphysics (5.0) software. The discharge coefficient (C_d)  for no sill height V-notch side weirs with no downstream weir ranged from 0.13 to 0.28. The (C_d) for no sill height V-notch side weirs with rectangular downstream weir ranged from 0.70 to 0.93 and that for 5cm sill height V-notch side weir with rectangular downstream weir ranged from 0.63 to 0.75. The relationship established with dimensional analysis is C_d = f (H/P, F_r, H/B, R_e, θ, S₀), indicating that the discharge coefficient is a function of the other parameters. Comparison of experimental and simulated results gave a good similarity with no sill height V-notch side weir, having 5cm rectangular downstream weir with Root Mean Square Error (RMSE) of 25% for 600 and 1% for 90^o and 120^o. However, there is a wide discrepancy for 5cm sill height V-notch side weir having 5cm rectangular downstream weir with RMSE that ranged from 30 to 57%.