Acrobatics of liquid ropes
Neil Ribe (FAST, Université Paris-Sud)
A thin `rope’ of viscous fluid falling from a sufficient height onto a surface forms a steadily rotating helical coil. Tabletop laboratory experiments in combination with a numerical model for slender fluid ropes reveal that finite-amplitude coiling can occur in four distinct regimes (viscous, gravitational, inertio-gravitational, and inertial) corresponding to different balances among the three principal forces acting on the rope. The model further shows that the onset of coiling has distinct viscous, gravitational and inertial modes that connect smoothly with the corresponding finite-amplitude regimes. I will also discuss some striking examples of non-stationary behavior of liquid ropes, including propagating spiral waves of air bubbles, supercoiling, and the `fluid mechanical sewing machine’ wherein the rope leaves complex `stitch’ patterns on a moving surface.