Polygons on a Rotating Fluid Surface

Abstract

We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat. We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate. The slight asymmetry induces a tendency for mode-locking between the plate and the polygon, where the polygon rotates by one corner for each complete rotation of the plate.

Cited by in corpus (9)

• Culinary fluid mechanics and other currents in food science
• Waves on a vortex: rays, rings and resonances
• Nonlinear Schrodinger Equation Solitons on Quantum Droplets
• Numerical study on the axisymmetric state in spherical Couette flow under unstable thermal stratification
• A deep-water closure model for surface waves on axisymmetric swirling flows
• Interfacial Instabilities in Torsional Flows
• The transition to aeration in two-phase mixing in stirred vessels
• Model for self-organized Leidenfrost rotating polygons as cnoidal waves
• Einstein, tea leaves, meandering rivers, and the origin of supermassive black holes in ekpyrotic universe