SIMULATION OF FLOW IN CIRCULAR CLARIFIERS WITH AND WITHOUT SWIRL

Axisymmetric numerical simulation with a finite-volume method and the kappa-epsilon turbulence model is described for the flow in a circular model settling tank with and without swirl. The geometry of the model tank requires the use of a nonorthogonal boundary fitted grid. Result s are compared with experimentally determined streamlines and flow-thr ough curves as well as with previous computations. For flow without sw irl, the numerical simulations are in good agreement with the experime ntal data, and significant improvement for a critical geometrical conf iguration was achieved by use of the low-diffusive HLPA discretization scheme for convection. The inclusion of swirl allows the model to acc ount for the influence of the circumferential removal procedure as wel l as for the effect of swirl inducing vanes at the inlet. The simplifi cation introduced in modeling the removal equipment impairs somewhat t he accuracy of the predicted now-through curves. For further improveme nt, a more realistic and detailed modeling of the swirl momentum and t urbulence production by the removal equipment is required, and complet e 3-D modeling may be needed.