Multiscale modeling of multiphase flow with complex interactions

This paper presents a variety of modeling and simulation methods for complex multiphase flow at microscopic, mesoscopic and macroscopic scales. Each method is discussed in terms of its scale-resolving capability and its relationship with other approaches. Examples of application are provided using a liquid–gas system, in which complex multiscale interactions exist among flow, turbulence, combustion and droplet dynamics. Large eddy simulation (LES) is employed to study the effects of a very large number of droplets on turbulent combustion in two configurations in a fixed laboratory frame. Direct numerical simulation (DNS) in a moving frame is then deployed to reveal detailed dynamic interactions between droplets and reaction zones. In both the LES and the DNS, evaporating droplets are modeled in a Lagrangian macroscopic approach, and have two-way couplings with the carrier gas phase. Finally, droplet collisions are studied using a multiple-relaxation-time lattice Boltzmann method (LBM). The LBM treats multiphase flow with real-fluid equations of state, which are stable and can cope with high density ratios. Examples of successful simulations of droplet coalescence and off-center separation are given. The paper ends with a summary of results and a discussion on hybrid multiscale approaches.