Vortex structures in a thin oscillating liquid layer

Formation of vortex flows in a thin oscillating liquid layers is investigated in experiments. Two cases are examined. In the first case, the liquid film has two free surfaces and is fixed horizontally along the edges of the cell vibrating in the vertical direction. The liquid contains surface active substance. Spatially homogeneous oscillations of the liquid film excite different types of waves which generate two-dimensional vortex flows due to nonlinearity. We present results of experimental investigation of the structure of vortex flows in a thin film (0.5-10 mc) for rectangular and hexagonal geometries of the boundaries. It is shown that a regular vortex structure with small-scale vortices (λ/2) repeats spatial distribution of the mode excited on a liquid membrane. It is revealed that with increasing amplitude of external force a regular structure collapses and large-scale vortices appear against the background of small vortices. It is shown that, for fixed parameters of the medium and external force, stable structures consisting of vortices of different shapes can arise depending on initial conditions. In the second case, we investigate vortices in a thin liquid layer poured on the rigid horizontal plate oscillating in the vertical direction. Oscillations generate capillary waves on a free surface of liquid (Faraday ripples), and we determine the condition of appearance of large-scale vortices. It is found that topological defects of Faraday ripples generate mean flows and can entrap and transport passive impurities. It is shown that a moving topological defect induces two vortices of opposite circulation moving together with it