Ribbing instability of Newtonian fluid coated on a topographic surface

Periodic wavy patterns emerge and align in a transverse direction once a viscous fluid is coated onto a surface moving above a critical speed. In this study, we examine how this flow instability, which is usually referred to as ribbing, is triggered or damped on a moving topographic surface. To examine the transient flow behavior, the liquid first came into contact with a smooth surface, followed by a downstream surface with small-scale V-shaped grooves. Flow visualizations revealed a topography-induced flow stabilization and a matching of rib frequencies with the underlying groove patterns, depending on the groove geometry and capillary number.