Author(s): Pablo Ouro, Bruno Fraga, Nicola Viti, Athanasios Angeloudis, Carlo Gualtieri, Thorsten Stoesser
Linked Author(s): Carlo Gualtieri
Keywords: Environmental hydraulics, hydrodynamics, solute transport, RANS/LES validation, disinfection contact tank
Abstract: Disinfection in contact tanks (CTs) is a treatment process applied for both drinking water and wastewater treatment systems with the purpose to inactivate micro-organisms, some of which may be pathogenic and thus preventing transmission of waterborne diseases. This paper presents the results of CFD simulations and validation of hydrodynamics and solute transport in the first two chambers of a chlorine contact tank comprised of a total of 8 compartments. Both RANS and LES methods are applied and successfully compared against experimental data for velocity and scalar concentration fields. Results outline the highly three dimensional behaviour of the flow with the presence of recirculating and short-circuiting zones. These phenomena enlarge the flow unsteadiness and turbulence affecting the instantaneous flow field, and therefore the transport of the released passive scalar. From the analysis of the average error percentage between numerical and experimental data of both simulations, LES provides greater detail in the hydrodynamics behaviour. Although RANS is able to reproduce the time-averaged flow properties quite well, LES conveys a larger amount of information on instantaneous flow field, which makes it capable to capture the flow unsteadiness that characterise the contact tank hydrodynamics and solute transport. Finally, using velocity component quadrant analysis of LES predictions, the turbulence field is found to be non-isotropic, an aspect not acknowledged in RANS
Year: 2017