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

TL;DR

This study uses ray-tracing visualization to compare droplet collision behaviors between Newtonian and non-Newtonian liquids, revealing differences in bouncing, coalescence, and instabilities like helical and buckling during stretching separation.

Contribution

It introduces detailed visualization of droplet collision dynamics and identifies specific instabilities in non-Newtonian liquids, highlighting the effects of shear-thinning properties.

Findings

Thinner gas film in shear-thinning liquids promotes coalescence.

Shear-thinning liquids have smaller bouncing regimes.

Helical and buckling instabilities occur during ligament breakup.

Abstract

In this video, Ray-tracing data visualization technique was used to obtain realistic and detailed flow motions during droplet collision. The differences of collision outcome between Newtonian and non-Newtonian were compared. Various types of droplet collision were presented, including bouncing, coalescence, and stretching separation. Because of the reducing of equivalent viscosity caused by shear stress, the gas film between shear-thinning droplet is thinner than Newtonian liquid. Since thinner gas film promotes coalescence, shear thinning liquid has smaller area of bouncing regime in the diagram of Weber number and impact parameter. During the ligament/thread breakup process of stretching separation, two kinds of instabilities are identified, helical and buckling instabilities. Helical instability is analogous to a viscous rotating liquid jet, while the buckling instability is analogous to electrically charged liquid jets of polymer solutions.