The Flow Field and Free Surface Pattern of the Submerged Side Weir with Different Lengths

A side weir is set in the side of a channel and is used for water level control, diverting excess water, as in sewage systems. In this study, firstly, a numerical simulation for prediction-free surface turbulent flow over the sharp crest side weir was performed by commercial software using the volume of fluid scheme and Reynolds-stress model (RSM) turbulence model. Comparison between numerical results and laboratory measurements showed that the model predicts experimental trends with reasonable accuracy. Then, the side weir length effects on the flow pattern and free surface were numerically investigated in the low, medium and high overflow rates. With decreasing the side weir length, the separation zone moves toward the downstream, and also the width of this zone and the distance of dividing stream surface from the left wall of the main channel were reduced at the free surface near the side weir crest level. In all cases, the side weir length and overflow rate variations had no any substantial effect on the secondary flow strength in main channel and the variations of the minimum water depth in the branch channel.