Study on the Characteristics of Gas–Liquid–Solid Three-Phase Unstable Flow in the Aeration Tank Driven by the Inverted Umbrella Aerator

The aim of this paper is to accurately simulate the three-phase, unstable flow characteristics in an aeration tank driven by an inverted umbrella aerator. Experimental data were used to fit the parameters of the Vesilind settling model in the aeration tank, with the following parameters: v 0 = 0.0023 and n = 0.3458, as well as the parameters of the Takács settling model, with v 0 = 0.0025, r h = 0.3972, and r p = 18.18. A method was developed to simulate the three-phase flow in the aeration tank driven by the inverted umbrella aerator. This was achieved by using the mixture model as the multiphase flow model and the standard κ – ε model as the turbulence model. The flow velocity and concentration at various measurement points in the tank were experimentally measured during stable operation of the aerator. Three different sludge settling models were used for numerical calculations: no settling model, Takács dual-exponential settling model, and Vesilind exponential settling model. The results showed that the relative average errors in concentration between the three models and the experiments were 68.7%, 5.43%, and 2.34%, respectively. The relative average errors in flow velocity were 45.12%, 26.06%, and 11.47%, respectively. It indicated that the Vesilind exponential settling model can more accurately describe the flow characteristics inside the aeration tank. An analysis based on the Vesilind exponential settling model revealed that gas is mainly distributed in the shallow water, while the volume fraction of sludge near the free liquid surface is unstable. The flow velocity is higher near the aerator impeller, gradually decreasing with increasing distance from the impeller until it reaches its maximum at the outer edge of the impeller. Turbulence intensity and turbulence energy are higher near the impeller, and decrease gradually as the depth increases in the deeper water. Graphical Abstract This article fitted different sludge settling models by measuring the sludge concentration and settling velocity at various points inside the aeration tank under the operation of an aerator. The Vesilind model was found to have the highest fitting degree. Further research using this model revealed the unstable three-phase flow pattern of gas–liquid–solid in the aeration tank.