Extending contactless manipulation strategies to fiber dispersions in microgravity

Recent advancements in microgravity-based, contactless manipulation strategies have opened exciting pathways for the production of advanced materials in space. These methods rely on the interplay between thermal stimuli applied to a fluid and high-frequency vibrations, creating novel opportunities for material synthesis that are not achievable under normal gravitational conditions. Originating from a theoretical framework formulated a decade ago, this approach has recently been validated through experiments on board the International Space Station (ISS). However, the scope of this theory and the associated experimental methodologies must now be extended to include cases where the dispersed elements are fibers rather than spherical particles. The shift from studying spherical particles to elongated fibers represents a crucial evolution of the theory, as fibers are a cornerstone of numerous materials science and engineering applications. Fibers, when dispersed in a matrix or liquid, exhibit unique behaviors due to their anisotropic geometry, which affects their dynamics, stability, and interactions with the surrounding medium. Understanding these phenomena under microgravity conditions could revolutionize our understanding and utilization of fiber-reinforced systems in advanced material design. In this study, the problem is approached numerically in the framework of a four-way coupling strategy. More precisely, while DEM (Discrete Element Method) is used to model individual fibers as discrete, deformable or rigid entities, capturing their translation, rotation, and collisions, on the other hand, CFD (Computational Fluid Dynamics) solves the fluid's governing equations (Navier-Stokes) to predict the host flow fields. Coupling these methods allows the fiber motions to be influenced by fluid forces (drag, lift, turbulence) while fibers reciprocally affect the fluid through momentum exchange. This synergy enables detailed analysis of fiber dispersion, orientation, and interactions in the considered problem.