Numerical Study of Flow Pattern, Sediment Field and Effect of the Arrangement of Guiding Blades (Baffles) on Sedimentation in Pre-Sedimentation Basins by Numerical Models

Pre settled pools were most important elements in water purification process. Because of enormous cost of making these pools which have been allocated about 30% of the total cost to water purification process Modeling and optimal performance of Pre settled pools is very important. The present study investigates numerical simulation of flow in a rectangular basin. Continuity and Navier-Stokes equations are solved using finite volume method. Flow simulation was performed in 3D using the different turbulence models. Flow velocity profiles were compared with the experimental results in different sections of Pre-sedimentation basin. The comparison shows that there is a good agreement between numerical and experimental study. Then, the results of the velocity profiles in different sections of the basin and flow separation zones were compared with the experimental results. It showed that there is a good agreement between the numerical and experimental results. It also indicates excellent ability of this numerical model in predicting velocity distribution profiles and flow separation zones in pre-sedimentation basins. Afterwards, in order to evaluate style of sedimentation in pre settled pool, diffusion and transfer of sediment concentration was solved simultaneously by hydraulic flow equations and finally results of vertical distribution of sediment profiles have been compared by laboratory result of other researcher which shows good adaptation of numerical results and laboratory results as well as capacity of this model to predict distribution of sediment profiles in pre settled pools. Near the free surface of the stream, the sediment concentration was decreased as in the outlet section of the basin, the sediment concentration near the free surface was decreased to 57.48% compared to the sediment concentration at the basin bottom.