Volume of Fluid Computations of Gas Entrainment and Void Fraction for Plunging Liquid Jets to Aerate Wastewater

摘要

Among various mechanisms for enhancing the interfacial area between gases and liquids,a vertical liquid jet striking a still liquid is considered an effective method. This method has vastindustrial and environmental applications, where a significant application of this method is to aerateindustrial effluents and wastewater treatment. Despite the huge interest and experimental andnumerical efforts made by the academic and scientific community in this topic, there is still a needof further study to realize improved theoretical and computational schemes to narrow the gapbetween the measured and the computed entrained air. The present study is a numerical attemptto highlight the air being entrained by water jet when it intrudes into a still water surface in a tankby the application of a Volume of Fluid (VOF) scheme. The VOF scheme, along with a piecewiselinear interface construction (PLIC) algorithm, is useful to follow the interface of the air and waterbubbly plume and thus can provide an estimate of the volume fraction for the gas and the liquid.Dimensionless scaling derived from the Fronde number and Reynolds number along with geometricsimilarities due to the liquid jet’s length and nozzle diameter have been incorporated to validate theexperimental data on air entrainment, penetration and void fraction. The VOF simulations for voidfraction and air-water mixing and air jet’s penetration into the water were found more comparable tothe measured values than those obtained using empirical and Euler-Euler methods. Although, smalloverestimates of air entrainment rate compared to the experiments have been found, however, VOFwas found effective in reducing the gap between measurements and simulations.