Polygons on a rotating thin-water layer: a combined experimental and numerical approach
Résumé
The flow of a thin fluid layer over a rotating disk is studied by direct numerical simulation and flow visualizations. The primary bifurcation appears as spectacular sharp-cornered polygonal patterns located along the outer casing. The stability diagram is established experimentally and confirmed numerically with a strong hysteresis between the spin-up and spin-down phases. These structures are induced by the appearance of a secondary flow. They rotate at a fre-quency, which slightly increases with the number of vortices. For larger Reynolds numbers, the polygons may coexist with a crossflow instability appearing as positive spirals.
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