Steady Flow Generated by an Interfacial Wave in an Oscillating Cell

The dynamics of the interface between two immiscible, low-viscosity liquids in a flat vertical cell are studied experimentally. The cell undergoes high-frequency, vertical translational vibrations. The liquids are characterized by a high-density contrast. In the absence of cell oscillations, the interface is horizontal and unperturbed. At low oscillation amplitudes, the interface oscillates together with the cell. The interface becomes unstable to the standing wave excitation when a critical amplitude is reached. A gravity-capillary standing wave oscillates at a frequency that is half that of the cell oscillations (Faraday wave). The Faraday wave is located in the plane of the cell. The height of the standing wave increases with the oscillation amplitude. It is found that the interface oscillations generate an intense steady vertical flow in the plane of the cell. Two symmetrical vortices are placed near each antinode of the wave. The height and length of the vortical pattern are consistent with the height and length of the standing wave. The fluid flows in a direction that is away from the interface at the antinodes of the standing wave and towards the interface at the nodes. The velocity of the vortical flow increases linearly with the square of the Reynolds number. Here, the Reynolds number is calculated through the amplitude of the wave oscillation velocity and the cell thickness. The phenomenon of the vortical flow excitation near the oscillating interface is of practical interest for the enhancement of the heat transfer in the cell.