Faraday instability in electrostatically forced liquid-air systems*

When stacked multi-fluid systems are periodically accelerated in a direction normal to the fluid interfaces, complex patterns on the interfaces develop as a result of resonance between the imposed oscillation frequency and the natural frequency of the system, a phenomenon known as Faraday instability. Experimental research at JAXA has successfully generated Faraday instability in electrostatically oscillated liquid-air systems constrained radially by insulating sidewalls and axially by externally controlled electrodes. In this work, we present the design and methodology for electrostatically oscillated experiments, experimentally determined stability curves, and the distinctions and commonalities between mechanically and electrostatically forced Faraday systems. Multiple geometries are examined in order to illustrate the effects of aspect ratio and sidewall boundary conditions. Pure AC forcing and AC forcing with a DC offset are both discussed. Videos of the generated patterns are shown and compared to theoretical predictions of their corresponding Faraday mode shapes. Subharmonic responses with respect to the base state oscillation of the system are observed upon the onset of the instability, a feature indicative of parametric instabilities.