This study is devoted to the experimental and theoretical investigation of aerodynamic drop breakup phenomena. We show that the phenomena of drop impact onto a rigid wall, drop binary collisions, and aerodynamic drop deformation are similar if the correct scaling is applied. Then we use observations of the deforming drop to estimate the evolution of the film thickness of the bag, the value that determines the size of the fine child drops produced by bag breakup. This prediction of film thickness, based on film kinematics, is validated for the initial stage by direct drop thickness measurements and at the latest stage by the data obtained from the velocity of hole expansion in the film. It is shown that the film thickness correlates well with the dimensionless position of the bag apex.

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Using high-speed video techniques, the influence of diluted polyether siloxane emulsions on the breakup mechanism of liquid spray films was investigated. First, the fragmentation of a single drop in an air flow, the so-called bag breakup, was used as a model system to study the ability of the polyether siloxane emulsion to control the breakup process. What was learned from these model experiments was then transferred to spray experiments using classical agricultural flat-fan nozzles. These demonstrated that polyether siloxane emulsions cause the nucleation of holes in an expanding liquid film, which leads to an accelerated, more uniform, and earlier breakup. Image-based drop size measurements confirmed that the promoted lamella breakup in turn leads to a considerable reduction of drift-prone droplets in the spray. Low-speed wind tunnel spray studies were conducted in order verify the findings from the high-speed video experiments.