(458g) Meso-Scale Direct Numerical Simulations of Mono-Disperse Bubbly Flows

Disperse gas-liquid flows involved in industrial application such as bubble columns are typically modeled using continuum hydrodynamic models, supplemented with Reynolds-average turbulence models to describe the effects of the fluctuations in the phase velocity on the mean flow properties. These turbulence models are derived assuming that the hydrodynamic model constitutes a reliable mesoscopic description of the multiphase system, and applying a phase averaging procedure. Numerous terms originate from the averaging procedure, such as, for example, phase turbulent kinetic energy production and dissipation, phase fraction – velocity correlation, pressure gradient – phase fraction covariance, which require closure. In this work we perform mesoscale direct numerical simulations of mono-disperse bubbly flows in the inhomogeneous regime, in order to establish the relevance and the behavior of each of the terms originated from the phase averaging procedure of the mesoscopic model as a function of the dispersed phase fraction. The computational domain under consideration is constituted by a three-dimensional column with squared cross-section. Periodic boundary conditions are applied to the sides of the column to avoid wall effects, while air is fed at the bottom, and pressure is fixed at the top. Simulations are performed for a range of inlet gas volume fraction between 1% and 50%, and for an inlet gas velocity between 0.01 and 0.03 m/s. The magnitude and the trends of the turbulent quantities and of the terms that originate from the phase averaging procedure are extracted from the mesoscale DNS and reported.