In the Master thesis, we designed a three-dimensional numerical model for predicting twophase flows that occur in gas-focused micro-jets of water-air. A mixture formulation is used
to describe the incompressible, Newtonian flow of water and focusing air, including a k-ω
SST turbulence model to ensure numerical stability. The numerical solution procedure is
based on the finite volume method with the volume of fluid method, which includes the
geometric reconstruction of the free surface. With appropriately chosen boundary and initial
conditions, such a model enables accurate, reproducible, mesh-independent and stable
numerical simulation of pressure and velocity fields. The numerical model is validated with
the results of measurements on a vertical, downward-positioned nozzle configuration. We
have developed a dedicated computer program to analyse the characteristic parameters of
micro-jets from experimentally obtained videos and numerical animations. The Reynolds
numbers of air and water in the numerical simulations are in the range 1009–2421 and
48–104, and the Weber number 0.57–3.0. Identical shapes of micro-jets are observed in
experimental videos and also in numerical animations for the same combination of air and
water volumetric flow rates. The model predicts well the average and local diameters of the
micro-jet. We have also analysed the temporal development of the jet breakup due to
instabilities. We have checked how the kinetic energy is transferred from the gas to the liquid
and noticed spots with locally increased values of the kinetic energy of the air.
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