Mesoscale flow structures origin

During the last two decades, the insight has gradually grown—thanks to advances in both experimental techniques and computational simulation tools—that many dispersed two-phase flows are dominated by dynamic mesoscale coherent structures in which particles, bubbles, or drops organize themselves. Evidence from experiments, hydrodynamic analyses, and computational simulations on the presence and dynamics of such structures, strands, and clusters is presented. Their origin being less well... 

The origin of mesoscale structures in dispersed multiphase flows may be investigated in three ways ... 

In addition to the attempts to better understand the origin of mesoscale structures in dispersed two-phase flows by means of extremum principles and stabflity analyses, CFD simulations may provide guidance. One may therefore expect that simulations of particle behavior on the basis of a proper description of the fluid—particle interaction force reproduce the formation and dynamics of coherent structures and clusters (see also Capecelatro et al, 2015). After all, CFD simulations allow visualizations of 3D transient flow fields and make it possible to systematically investigate the effect of all types of variables (flow rates, physical properties, geometrical parameters) on flow fields to a degree not feasible experimentally. 

It is the author s conviction that in many (turbulent) dispersed multiphase flows—except probably in very dense multiphase flow systems—the origin of mesoscale structures is in the fluid—particle interaction, with a secondary role for particle-particle interaction (coUisions, coalescence, breakup). Clustering of particles is believed to be intimately connected with the chaotic dynamics of fluid accelerations, as particles converge toward each other where and when the divergence of the acceleration field is positive (Goto... 

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