Experimental investigations on the nonequilibrium dynamics of pattern formation in fluid and granular systems

Patterns are quotidian in nature. Distinct multiscale patterns are generally a consequence of nonequilibrium dynamical processes associated with mechanical or hydrodynamic instabilities. In this thesis, I report experimental investigations on pattern formation in a few examples of fluid and granular systems, and uncover the underlying mechanisms that give rise to those patterns. Leidenfrost drops are known to experience star-shaped oscillations with little damping. However, the underlying mechanism remains unclear. Here I report that the hydrodynamic coupling between the rapid evaporated vapor flow and vapor-liquid interface excites the star-shaped oscillations, suggesting a purely hydrodynamic origin. Polygonal desiccation crack patterns are commonly observed in natural systems. However, it is unclear whether similar crack patterns spanning multiple length scales share the same underlying physics. I report experimental results on polygonal cracks in drying suspensions of micron-sized particles. In cornstarch-water mixtures, multi-scale crack patterns were observed due to two distinct desiccation mechanisms. We also find the characteristic area of the polygonal cracks, and film thickness obey a universal power law. Finally, I report sedimentations of non-Brownian particles in viscous fluids. We observed an effective repulsion between particles with nonuniform density in both two-body and many-body systems in two and three dimensions, in contrast to particles with uniform density. We also characterize the statistical properties of the sedimentation patterns of particles in three dimensions. The patterns I report in this thesis represent typical examples in fluid and granular systems that are driven by nonequilibrium dynamics, and the underlying mechanisms we uncover are expected to enhance our understanding of how these seemingly simple patterns arise in natural systems.