Blowing drops off a filament

Abstract

The first part of this work is devoted to the experimental study of oil drop motion along a filament due to the parallel air jet blowing. The drop displacement and velocity along the filament are measured. A number of accompanying phenomena are observed. These include drop stick–slip motion and shape oscillations, shedding of a tail along the filament, the tail capillary instability and drop recoil motion. The experimental observations are rationalized in the framework of several simplified models, and the origin of several observed phenomena is elucidated. In the second part of this work, experiments with cross-flow of the surrounding gas relative to the filament with an oil drop on it are conducted, with the gas velocity being in the 7.23 to 22.7 m s⁻¹ range. The Weber number varied from 2 to 40 and the Ohnesorge number was in the 0.07 to 0.8 range. The lower and upper critical Weber numbers were introduced to distinguish between the beginning of the drop blowing off the filament and the onset of the bag-stamen drop breakup. The range of the Weber number between these two critical values is filled with three types of vibrational breakup: V1 (a balloon-like drop being blown off), V2 (a drop on a single stamen being blown off), and V3 (a drop on a double stamen being blown off). At still higher values of the Weber number, the bag-stamen breakup can be replaced by the bag type of breakup depending on a slight difference in the blowing speed, or the former and the latter can become intermittent depending on the drop asymmetry relative to the filament. The Weber number/Ohnesorge number plane was delineated into domains corresponding to different breakup regimes, the statistics of the residual liquid portion left on a filament was established and drop hopping across neighboring filaments was studied.