Granular plugs

A repeating pattern of granular plugs emerges when a tube filled with water and grains is slowly drained. The moving air-water meniscus bulldozes the grains ahead, and friction eventually causes the grains to jam, forcing the air to penetrate through the accumulated material. Once through to the other side, the air starts to pile up another plug, and the process repeats until the whole tube is clogged full of granular plugs separated by empty gaps.

Dumazer et al., Frictional Fluid Dynamics and Plug Formation in Multiphase Millifluidic Flow. Phys. Rev. Lett. 117, 028002 – Published 7 July 2016. Dumazer_PRL028002

Patterns in film flow

Time lapse movie of pattern formation in a drying particulate suspension. A mixture of silicon dioxide particles and water is spread out on a horizontal glass slide, and evaporation generates a flow from the center towards the edge of the droplet. Large particles become pinned to the substrate by the fluid meniscus, and act like obstacles to the flow. Gradually smaller particles become trapped by the meniscus, and deposits grow sideways into irregular stripes. Patterns like these can be seen on the sides of muddy cars on rainy days.

Frictional Fluids II

This movie shows what happens when you inject a gas into a granular suspension at different injection rates. At low rates, “stick slip” bubbles emerge, followed by “temporal intermittency” where periods of continuous motion are interrupted by occasional jamming. Increasing the injection rate further produces a spectacular “coral”-like pattern, and ultimately destabilized viscous fingers appear at high rates.