Drag reduction studied by splashing visualization

Abstract

The splash is a phenomenon which happens on droplet impact against a shallow liquid surface (target), forming a structure called crown. After the collapse of the crown, a liquid column (Rayleigh jet) arises on the surface. Splashing has been studied from a great variety of viewpoints, in different fields such as: agronomy, biology, engineering, astronomy, photography and marketing. The visualization of the splash was used, in our case, to study the drag reduction effect that happens when very low concentrations of a high molecular weight polymer is present in the fluid under investigation. We have developed a controlled drop-releasing device, fitted with a high-speed CCD camera [with shutter speed of 1/10000 s], and an image acquisition and processing system. Using this assembly, it was possible to observe large changes in the splash structures of water, especially in the extension of the Rayleigh jet. This result was associated with the drag reduction effect produced by the polymer. Result obtained with the dyed drop technique has shown that the presence of the polymer affects the mixture of the liquids from the droplet and target.