Transient impact of a liquid column on a miscible liquid surface

The flow induced by a liquid column falling on an undisturbed liquid surface is studied with the aid of a high-speed camera. The falling liquid spreads over the receiving liquid forming a cavity which eventually pinches off due to the action of gravity. It is only at this point that the normal flow pattern in which the impacting liquid penetrates below the free surface is established. The same process—at a scale smaller by four orders of magnitude—is encountered in the jetting behavior of collapsing cavitation bubbles. It is also observed that the cavity dynamics is strikingly similar to that found when a disturbance is induced on a steady jet falling on a liquid. This observation supports a generic mechanism for air entrainment hypothesized in an earlier paper.