External Flow of an Acoustically Levitated Droplet

One of the major recent advances for experiments in containerless processing is acoustic levitation. Although there are a lot of previous studies for acoustic levitation, characteristic of external flow of an acoustically levitated droplet is not experimentally examined enough. In this study, external flow field has been observed by using high speed camera and Particle Image Velocimetry. In the case of any levitated droplet at a velocity antinode of standing wave, toroidal vortex are generated around levitated droplet. It is found that toroidal vortex around a levitated droplet is strongly affected by viscosity of levitated samples and input voltage. In terms of water droplet, as input voltage is decreased, location of toroidal vortex is moved from bottom to top of levitated samples.