Experimental study of vortices and cavities from single and double drop impacts onto deep pools

In the present work, experimental investigations of single and double drop impacts into a deep pool of the same liquid are presented. For the first time, vortex interactions of two synchronised spherical drops of equal size are presented and compared to the evolution of undisturbed vortex rings generated by single drop impacts. High-speed images show novel and not yet documented vortex structures. The results show that vortex rings can be generated for drop Weber numbers well above the boundaries given in the literature, but with a different structure. Reynolds numbers of the relaminarised vortex rings depend on the presence of an outer vortex ring and are found to be significantly lower, if this structure was suppressed. (C) 2016 Elsevier Masson SAS. All rights reserved.