Bowling water drops on water surface

Abstract

In our daily experience, the drops falling on a water pool usually immediately merge into water. The liquid drops floating at different environments are fascinating but attract less attention. Here, we report that the water drops are capable of floating on a water surface without heating, shearing, or oscillating the water pool. Water drops are generated from a beveled needle and fall on the clean water in an acrylic container. Water drops released from a beveled needle are found to travel on the water surface in a speed of tens of millimeter/second for several centimeters, which can be adjusted by the injection rate. A particle image velocimetry (PIV) technique is employed on the air, water drop, and water pool to confirm the rotation-induced shear effect for the delay coalescence. TiO2 particles and water aerosols served as visualized particles for PIV measurements in air, drop, and water pool. We show that the water drop can float on the water surface if it rotates or slides fast enough. The relative motion of the drop and the underneath surface plays an important role in the delay coalescence. The flow in the air layer between the drop and water pool not only shears the drop but also replenishes the loss of squeeze-out air in the thin layer.