To reveal and understand the jet formation, we performed experiments in a 2D setup, with a disk being dropped between two perspex walls 15 mm apart. The jet now takes the form of a sheet. The pictures below show how the splash is formed upon impact, and the collapse of the void. Air is entrained below the closure. Two jets are formed: one upward, and one downward (into the bubble). The focused pressure is weaker than in 3D, and hence the jets are less spectacular. In the final frames the bubble is seen to slowly rise to the surface, and a small eruption rounds off the series of events.
For a full account, our 2002 Gallery of Fluid Motion winning entry can be downloaded here (NB!!! 44MB).
Participants in the project
René Mikkelsen, Michel Versluis, Elmer Koene, Gert-Wim Bruggert, Devaraj van der Meer, Ko van der Weele, and Detlef Lohse,
Phys. Fluid, in press (September 2002).