MODELING FLOW AND MIXING IN SEDIMENTATION TANKS

Numerical results from a computer model for the prediction of the neutrally buoyant flow within sewage treatment plant settling basins are compared with results of several new experiments. The flow field calculations performed using the k-∈ turbulence model agree well with experiments for simple geometries. The quality of the computations, however, deteriorates with increasing flow complexity. It is argued that the effects of flow curvature, which are not included in the standard k-∈ model, are mainly responsible for the differences between computation and experiment. The results of the calculation of dye transport within the basin after pulse injection show that the use of low-order numerical models results in predictions in which the solution is badly polluted by numerical errors. The quality of the prediction of the dye concentration field is strongly related, to the quality of the flow field prediction. The passing time of the peak output concentration is well predicted if the size of the recirculation regions is well predicted. In all cases, the peak dye concentration is overpredicted. © ASCE.