Computational study of bubbly jets in stagnant water

The air-water bubbly jets in a stagnant water are numerically investigated by using a CFD software package with the realizable k-e turbulence model.The focus is on the jet evolutionary behaviors in terms of the gas void fraction,the axial water velocity,the turbulent kinetic energy(TKE),the entrainment coefficient,and the momentum and buoyancy fluxes in a wide range of the bubbly jets(with the initial gas volume fractions ranging from 0 to 0.83).The computational results are found generally in good agreement with the experimental results reported in the literature.Both the gas void fraction and the axial water velocity follow the Gaussian distribution in the radial direction as expected,however a double-peak distribution is found for the TKE at some distance away from the nozzle.With the increase of the longitudinal distance,their peak values generally are decreased until reaching approximately their terminal values.The non-dimensional relations are revealed in both the radial and longitudinal directions.The potential core and the spreading rates of the bubbly jets are then investigated.The liquid volume flux of the bubbly jets is found to increase almost linearly along the centerline with an entrainment coefficient of 0.037-0.065.The momentum flux of the bubbly jets increases due to the buoyancy force,and the relative importance of the momentum and buoyancy fluxes is also discussed.

Oxygen transfer characteristics of bubbly jet in regular waves

The dissolved oxygen level is an important index of the water environment,and in this paper,the oxygen transfer of the bubbly jet in regular waves is investigated numerically and experimentally.The Reynolds-averaged Navier-Stokes equations,the re-normalisation group k-e equations,and the volume of fluid(VOF)technique are used along with a 2-D CFD model to simulate the wave and bubble motions as well as the turbulence,and a dissolved oxygen transport equation is used to model the oxygen transfer behavior both through the bubbly interface and the wave surface.A series of experiments are conducted to validate the mathematical model,with good agreement.In addition,a group of dimensionless parameters are defined from the wave parameter and the aeration parameter,and their relationships with the total oxygen transfer coefficient are explored.Furthermore,the dimensional analysis and the least squares methods are used to derive simple prediction formulas for the total oxygen transfer coefficient,and they are validated with the related experimental data.