ROTATING SPIRALS IN A FARADAY EXPERIMENT

We report experiments and model simulations of patterns of parametrica lly excited capillary ripples in a large aspect-ratio cell with thin h orizontal layer of viscous fluid subjected to sinusoidal vertical osci llations. We found stable rotating spirals with different topological charges in the parameter range where steady straight rolls were observ ed previously. Formation of multiarmed spirals via dislocations approa ching a target core was observed. The direction of the spiral rotation depends on its chirality and is always consistent with wave propagati on towards the core. Wave drift towards the spiral core is associated with the shear flow which is generated near the walls by rapidly decay ing viscous surface waves.