Large Bubble-Resolved Direct Numerical Simulation for Multiphase Flow Applied to Gas-Stirred Ladles: Grid Resolution and Plug Eccentricity Effects

There is a need for bubble-scale modeling of bubbly multiphase turbulent flow in gas-stirred reactors, with a direct resolution of bubble formation, bubble shape, bubble deformation, bubble coalescence and breakup phenomena. A large dispersed-phase resolved direct numerical simulation (LDPR-DNS) based on a fine grid volume of fluid was proposed in our previous work and employed in understanding multiscale phenomena in gas- or mechanically stirred ladles. A remaining challenge is how to determine the required grid resolution for targeted phenomena, particularly when large eddy simulation (LES) is used to resolve the turbulence of dispersed multiphase flow. In this study, we first review the evolution of multiphase flow models and their gaps in the context of a multiscale framework and then clarify the advantages of LDPR-DNS by comparing it with the traditional computational fluid dynamics of multiphase systems. A particular focus was identifying a suitable grid spacing for LDPR-DNS with LES, and several grid schemes were carefully investigated in terms of whether the bubble-scale related flow phenomena are effectively resolved, the LES model realistically captures the utmost part of turbulence, and the balance of interfacial energy transfer between two phases is precisely closed. Finally, the model with a high-resolution grid was applied to reveal the effect of eccentricity on flow pattern, large-scale interface profile and open eye, energy transfer efficiency, inactive zone distribution, and features of the turbulent kinetic energy and its dissipation rate, with a resolution of bubbles. The established LDPR-DNS will tremendously boost the multiphase flow simulation toward a smaller spatio-temporal scale and more complex phenomena.