The Control of Fluids in Microgravity with Vibrations (CFVib) experiment was selected for the 2016 Fly Your Thesis! programme as part of the 65th ESA Parabolic Flight Campaign. The aim of the project is to observe the potentially complex behaviour of vibrated liquids in weightless environments and to investigate the extent to which small-amplitude vibrations can be used to influence and control this behaviour. Piezoelectric materials are used to generate high-frequency vibrations to drive surface waves and large-scale reorientation of the interface. The theory of vibroequilibria, which treats the quasi-stationary surface configurations achieved by this reorientation, was used to predict interesting parameter regimes and interpret fluid behaviour. Here we describe the scientific motivation, objectives, and design of the experiment.

Experiments on vibrated fluids confined in cylindrical and cuboidal containers were performed under the reduced gravity conditions of a parabolic flight. The results constitute a systematic quantitative investigation of the vibroequilibria effect, which refers to the reorientation of vibrated fluids in response to the inhomogeneous oscillatory velocity field and the accompanying dynamic pressure. This effect is amplified in microgravity where the restoring force of gravity is small or absent. Here the vibrations are transmitted via a pair of piezoelectric ceramics and a cantilever beam, excited in a resonant mode. The first and second resonances exhibit different types of motion and lead to different types of vibroequilibria surfaces, one with a dip or crater in the interior and the other flattened compared to the unforced reference experiment. The general tendency for interfaces to orient more perpendicular, on average, to the vibrational axis is confirmed. In the case of water in a cuboidal container, a quantitative comparison is made with vibroequilibria theory and with direct simulations of the Navier-Stokes equations. The good agreement confirms the predictions of vibroequilibria theory and suggests the capacity of this phenomenon to manipulate and position fluids in space environments through the choice of frequency and resonant mode.