Do we understand the bubble formation by a single drop impacting upon liquid surface?

Large bubble formation by a single drop impacting upon a liquid surface with low impact energy is conventionally considered to be unimportant and not a cause for small bubble(s) generation. Our experiments contradict three widely accepted concepts about bubble formation. First, this paper presents results that give evidence of much wider existence of large bubble entrainment. Second, there is no closed characteristic regime for regular large bubble generation. Third, for the first time, there are results of bubble pair generation in sequence that show the direct formation of smaller bubble(s) due to a single large bubble rupturing without external disturbances. Additionally, this work demonstrates that the shape of an oscillating prolate drop at impact is the missing factor that helps predict large bubble formation. At the end, this paper presents a new characteristic map for large bubble formation that is based on the theoretical oscillation model. (C) 2013 AIP Publishing LLC.