Vertically-Vibrated Gas-Liquid Interfaces: Surface Deformation and Breakup

Abstract

In his pioneering work of 1831, Faraday demonstrated that a vertically vibrated gas-liquid interface exhibits a period-doubling bifurcation from a flat state to a wavy configuration at certain frequencies or amplitudes. Typical experiments performed using thin layers of water produce "Faraday ripples", modest-amplitude nonlinear standing waves. Later experiments by Hashimoto and Sudo (1980) and Jameson (1966) as well as those performed in the present study show that much more dramatic disturbances can be generated at the gas-liquid free surface under certain ranges of vibration conditions. This breakup mechanism was examined experimentally using deep layers of polydimethylsiloxane (PDMS) silicone oils over a range of viscosity and sinusoidal, primarily axial vibration conditions that can produce dramatic disturbances at the gas-liquid free surface. Large-amplitude vibrations produce liquid jets into the gas, droplets pinching off from the jets, gas cavities in the liquid from droplet impact, and bubble transport below the interface, all of which can be seen in the videos. Experiments were performed using several different PDMS silicone oils covering a range of viscosity (1-50 cSt, i.e., 1-50 times nominal water) and relatively low surface tension (e.g., 0.25 times nominal water) over a range of vibration conditions (100-150 Hz, less than 300 micron displacement, yielding accelerations ranging from 4 to 7 times gravitational acceleration). The cylinder containing the silicone oil was 25.4 mm inner diameter and approximately 100 mm long. It was typically filled halfway with the PDMS liquid, with ambient air above. High-speed videos were recorded at 600 to 1000 frames per second. Applications include liquid fuel rockets, inertial sensing devices, moving vehicles, mixing processes, and acoustic excitation.