Particle accumulation structures in non-cylindrical liquid bridges under microgravity conditions

Capobianchi, Paolo and Lappa, Marcello (2020) Particle accumulation structures in non-cylindrical liquid bridges under microgravity conditions. Physical Review Fluids, 5 (8). 084304. ISSN 2469-990X

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    The emergence of particle accumulation structures (PAS) in noncylindrical liquid bridges (LBs) is studied numerically for a high Prandtl number liquid considering microgravity conditions. Simulations are conducted in the framework of a finite-volume (Eulerian) approach with nonisodense particles tracked using a Lagrangian, one-way coupling scheme. First, the threshold of the Marangoni-flow instability is determined as a function of the aspect ratio and the volume of liquid held between the supporting disks, thereafter, PAS formation is investigated for supercritical conditions. The overall approach is specifically conceived to provide details about the morphological evolution of these structures as the main control parameters are varied. For this reason a set of dedicated notions and definitions (such as the linear extension of the PAS, its inner core radius, and the area of the "petals"or "blades") are introduced to allow a precise quantification of a series of purely geometrical effects. Though the analysis is deliberately limited to illustrating the macroscopic patterning behavior and its relationship with the overarching factors, a model is proposed to interpret the increased ability of slender (concave) LBs to support the formation of PAS over extended ranges of values of the particle Stokes number. This model yet relies on essentially geometrical arguments, that is, the triadic relationship among the curvature of the free surface, the topology of fluid streamlines, and particle mass effects.