CFD Simulation Of Oxidation Ditches Driven By Inverse Umbrella Surface Aerator

The hydrodynamic characteristics play significant roles in design and operation of oxidation ditches. With the help of computational fluid dynamics (CFD), the hydrodynamic characteristics of oxidation ditches can be understood. In this study, based on numerical simulation of the inverse umbrella surface aerator in the oxidation ditch, the developed momentum source term model has been improved, then a method of predicting the power of the surface aerator and a way to value the propelling performance of the surface aerator have been proposed. First of all, the existing momentum source term model (Model I) and two improved momentum source term model (Model II and Model III) were used to investigate the flow characteristics in a Rushton turbine stirred vessel, then the calculated results were compared with the huge reported experimental data, as well as with the results simulated by multiple reference frame(MRF) and sliding mesh(SM), which showed the results of the improved momentum source term Model III were most agreed with the experimental data. It is suggested that Model III is a reliable approach and the proposed power predicting method is feasible. After that, Model III was used to simulate the flow field of the test oxidation ditch driven by an inverse umbrella surface aerator. The results from different turbulence models and impeller models were compared, as well as compared to the experimental data, which further proves that Model III can be applied to simulate the flow in oxidation ditch driving by the inverse umbrella surface aerator and the power of the aerator can be well predicted. In the end, on basis of the simulated flow field of the oxidation ditch driven by different inverse umbrella surface aerators, their propelling performances have been valued. Also, the flow distributions on several operating conditions of a full-scale carrousel oxidation ditch have been predicted with the Model III.