Numerical study of the effect of length change on the flow pattern around a side weir in a converging channel

Side weirs are among hydraulic structures which are utilized in flood control, urban sewage disposal networks, irrigation, and drainage channels. Today, thanks to computer science advancement, the use of numerical models has been increased owing to lesser time and lower costs compared with experimental models. The present study deals with investigating the flow pattern on a side weir in a converging rectangular channel using a commercial software employing RNG turbulence model and VOF method to simulate turbulence and free surface, respectively. One of the advantages of using side weirs is that after drainage it is unnecessary to continue the downstream channel with the previous width, and consequently it will be cost-effective. Comparing longitudinal velocities, water surface profiles, and flow discharge over a side weir with experimental results indicated the capability of the numerical model to simulate the flow pattern over a side weir. The effects of length changes of the side weir on the flow characteristics also were studied. Comparing parameters in different sections at the middle of the side weir showed that decreasing the length of the side weir increases the longitudinal velocity. Also, by decreasing the side weir length the passing discharge declined, and the free surface profile formed in higher height as well. The discrepancy between the specific energy at the upstream and that of the downstream of the weir for different side weir lengths was negligible.