Laboratory measurements of spontaneous oscillations for moderate- size raindrops

Abstract

The natural oscillations of moderate-size raindrops were studied in a seven-story fall column using a computer-controlled generator to produce isolated water drops at terminal speed. Instantaneous shapes were photographed to obtain oscillation sequences of single drops by a multiple-strobe technique. Variations as large as 15% in axis ratio were observed at the bottom of the fall column, even though the initial oscillations were predicted to die out by viscous decay theory. Practically all oscillations were at the fundamental and first harmonic-frequencies. The oscillation modes deduced from the axis ratio scatter indicated that the axisymmetric modes died away slowly and that transverse modes persisted. -from Authors