Numerical simulation of turbulent two-phase flows

Abstract

A two-equation turbulent model for steady incompressible two-phase flows was developed to predict multiphase flow phenomenon from the Navier-Stokes equations. Turbulent two-phase bubbly noncondensing jet flows and pipe flows were investigated. The numerical computations used an Eulerian system to describe the continuous (liquid) phase and a Lagrangian approach for simulating the effects of the dispersed (gaseous) phase. Source terms were used to couple the two approaches. A deterministic separated flow model was used to predict the bubbly jets, whereas a stochastic separated flow model was developed to describe the bubbly flow in vertical pipes. The deterministic model allows for bubble interactions with the liquid mean properties, whereas the stochastic model takes into account the instantaneous transport properties of the bubbles and the liquid. The addition of even small amounts of air increases flow turbulence levels noticeably. At higher void fractions, the effects of the second phase were large, justifying the need for a detailed model of the energy production and dissipation mechanisms to predict the two-phase flow. These effects were included in the k- ϵ model of turbulence used here and required introduction of two additional constants for closure. The additional constants were evaluated using the limited experimental data available. The model's two-phase flow computations yielded very good predictions of flow details. Predictions of the radial distributions of mean velocity and turbulence intensity compared well with the experimental data available in the literature.