Research on key factors for the drop evolution process in ambient liquid under an impact

Abstract

A mixed flow of two immiscible liquids may form drops of one liquid in another. Deformation and breakup of a drop will occur when there is sufficiently severe interaction between the drop and the ambient liquid. In this paper, the drop evolution process in ambient liquid under an impact was studied based on an experimental method combined with computational fluid dynamics (CFD). In the experiment conducted on a free-falling drop-tower facility, four typical drop deformation modes, namely oscillatory mode, bag mode, cap mode, and mushroom mode, sorting in order of deformation severity, were captured with high speed photography. In the numerical simulation, the Front-Tracking method was adopted to predict the drop evolution process, and a satisfactory agreement was obtained between the experimental and numerical results. After the verification a further numerical analysis was carried out for the mechanism of the four types of drop deformation modes before the breakup of liquid film, for which the key factors that dominate the drop evolution process were also discussed. It is found that the drop evolution is strongly affected by vortex strength, namely the greater the vortex strength is, the more severe the evolution mode will be, during which an annular jet will be generated and continues to turn over; on the contrary, there is no annular jet formation or even drop deformation recovery phenomenon occurs. After a further research on the generation and development of the annular jet inside the drop, we find that there is a competition mechanism between vortex evolution and interfacial constrain, in which deformation of the interface is promoted by vortex evolution, while interface constrain plays an inhibitory role. Finally, the competitive mechanism has been further revealed by the numerical results of drops deformation under the conditions with/without interfacial tension.