Document Type: Original Article
Department of Civil Engineering, Central Tehran branch, Islamic Azad University, Tehran, Iran
Department of Civil Engineering, South Tehran branch, Islamic Azad University, Tehran, Iran
Pre-sedimentation basins are among the most important elements of the conventional water treatment process. In pre-sedimentation basins, due to different velocity gradients, secondary and rotational flows are formed that will create short paths and increase dead and still flow zones as well as changes in the flow mixing. This will prevent laminar flow conditions for sedimentation and will reduce the basin efficiency. The first step in optimization of the pre-sedimentation basins is the correct calculation of the velocity field and rotating zones volume. In this study, flow in a rectangular basin was simulated numerically and continuity and Novier-Stokes equations were solved using the Finite Volume method. 3-D flow simulation was performed using standard k-ε turbulence model and flow velocity profiles at different sections of the pre-sedimentation basin were compared with the experimental results and the results were in good agreement. Then, in order to investigate the sedimentation pattern in pre-sedimentation basin, convection-diffusion equation of the sediment concentration was simultaneously solved with the governing equations of the flow hydraulics. Finally, vertical distribution of sediment concentration at different basin sections was compared with the experimental and numerical results of other researchers. The results indicated a good agreement between the numerical and experimental results as well as the model ability to predict sediment distribution profiles in pre-sedimentation basins.