Hydrodynamics and Acoustics of the Merging of a Drop with a Liquid in an Electrostatic Field

The flow pattern and the sonic wave trains formed during the merging of a drop of distilled water with water surface in an electrostatic field with a potential of 2 kV synchronously recorded for the first time on the CDD (Charged Drop Dynamics) rig, which forms a part of the unique GFK IPMech RAS equipment. The experiments were carried out in the impact mode, when the falling drop forms a cavity, a splash, and a secondary cavity, from which a gas cavity separates and emits a retarding sonic wave packet. In an electrostatic field, a sound-emitting bubble of complex shape separates from the cylindrical end of the second cavity without forming a thin bridge observable when the bubble separates when the voltage is turned off. Selections from a video film illustrating the evolution of the fine flow structure during sound generation are presented together with the chronogram of the position of the lowest point of the cavity and an audiogram of the acoustic pressure. The primary and retarded sound packets, in which both the amplitudes and the basic frequencies vary nonmonotonically, are separated out and analyzed.