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Abstract

A vortex settling basin (VSB), consisting of a cylindrical chamber, an inflow system, a bottom orifice outflow and an overflow weir, has been used to separate sediment from sediment-laden water flow. The efficiency of sediment extraction by a VSB is significantly dependent on the flow characteristics of the device. The vortex in a VSB is complex and it is very difficult if not impossible to measure it by using a direct measurement. The VSB used in this study has a cylinder of 100 cm in diameter and 30 cm in height, with an overflow weir 15 cm height above the bottom. This study numerically assessed the velocity distribution in the VSB by using FLOW-3D. Comparison of the water surface profiles obtained from experiments and simulations shows that the simulated results are quite close to the experimental results, and this indicates that FLOW-3D is a suitable software for simulating flow field in a VSB. The comparisons between inflow depth and outflow discharges indicate there is less than 3.46% error between the numerical output and experimental data. Simulated velocity distributions at the depths of 6.3 cm (the distance from the bottom), 10.3 cm, and 14.3 cm (near the surface layer) were analyzed, respectively. The characteristics of velocity components (tangential, radial, and axial velocities) at these three depths were considered, in addition to the velocity distributions, the formation of an air core in the central part of vortex flow was also simulated and considered. Both the experimental and numerical results show the existence of air core oscillation. The oscillation may cause some changes in the flow field, especially in the high velocity zone, but the overall change in the whole flow field is not obvious.

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