Bouncing, Helical and Buckling Instabilities During Droplet Collision: Newtonian and Non-Newtonian Liquids

摘要

In this video, Ray-tracing data visualization technique was used to obtainrealistic and detailed flow motions during droplet collision. The differencesof collision outcome between Newtonian and non-Newtonian were compared. Varioustypes of droplet collision were presented, including bouncing, coalescence, andstretching separation. Because of the reducing of equivalent viscosity causedby shear stress, the gas film between shear-thinning droplet is thinner thanNewtonian liquid. Since thinner gas film promotes coalescence, shear thinningliquid has smaller area of bouncing regime in the diagram of Weber number andimpact parameter. During the ligament/thread breakup process of stretchingseparation, two kinds of instabilities are identified, helical and bucklinginstabilities. Helical instability is analogous to a viscous rotating liquidjet, while the buckling instability is analogous to electrically charged liquidjets of polymer solutions.