Oscillatory Motion of a Droplet Cluster

Horizontal oscillations of small droplet clusters (from one to four droplets) levitating over a locally heated water layer in upward vapor–air flow are investigated experimentally. These oscillations are caused by a complex dynamic interaction between the droplets and the nonsteady gas flow. The path of the center of the droplet cluster is similar to a random walk in a potential well. The vibrational spectra of clusters’ centers obtained by Fourier analysis showed several frequency peaks between f = 1.61 and 5.96 Hz found in all clusters, which shows that the cluster tends to oscillate as a whole. The possibility of decoupling of the aerodynamic interaction between the gas flow and the droplets and the interaction between individual droplets is discussed.