مهندسی عمران شریف (Feb 2020)
EXPERIMENTAL AND NUMERICAL MODELING OF FLOW FIELD WITHIN A VORTEX SETTLING BASIN
Abstract
A vortex settling basin (VSB) is an efficient continuous flushing system to remove sediment in water and wastewater treatment plants. Although many researchers studied this device experimentally, but the complex flow field has not been studied comprehensively. In current study, experimental study was conducted at Ferdowsi University of Mashhad, Iran on a laboratory setup made of Perspex sheet that is comprised of the inlet channel (4 m long, 0.20 m wide, and 0.3m deep), cylindrical chamber (1m m diameter), bottom slope of 1:10 toward the central orifice (0.1m diameter) and outlet channel (3 m long, 0.20m wide, and 0.3 m deep). The 3D velocity field in an experimental VSB was measured by Acoustic Doppler Velocimetry. The effects of vortex generation on basin performance and flow properties (tangential, radial, and axial velocity components) in the VSB were analyzed. Secondary currents were highlighted as important phenomena in settling of sediment particles and their flushing through the bottom orifice. data Moreover, the flow field was calculated using 3-D RANS models including standard k-$\varepsilon$ and k-$\omega$ models and LES-Smagorinsky model; the SIMPLE algorithm was used for velocity-pressure coupling, and the free surface was simulated using the VOF method. The results of numerical simulation were compared to experimental data including Standard k-$\varepsilon$, k-$\omega$ and Smagorinsky models; which Smagorinsky model was superior. The Smagorinsky model satisfactorily simulated the overall pattern of the secondary currents in the VSB although all the simulations had a similar flow field and location of generated vortex and direction of flow were the same. Formation of a force vortex near the bottom orifice and a free vortex in the outer region toward the basin periphery was similar to experimental data. velocity measurements were time averaged value while generated vortex inside the VSB had an unsteady behavior. Therefore, differences between experimental and numerical data are expected.
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