Vertical Oscillations of Water Droplets in the Supporting Vapour–Air Flow

A microscopic-size droplet levitates steadily in a vapor–air flow rising upward over a locally heated thin water layer. A Fourier analysis of the droplet position during a high-speed video recording revealed small-amplitude high-frequency droplet oscillations. This study focuses on overcoming the noise hindering extraction of oscillatory modes from spectra. The analysis revealed that some modes are associated with the horizontal droplet motion, while the others are due to the vertical motion. Possible physical reasons for the onset of this oscillatory motion are briefly discussed. Along with a single droplet, small clusters consisting of two or three droplets are considered.