Completing the story of aerobreakup with the analysis of shear-thickening liquids

Understanding interfacial instabilities is fundamental to analyzing breakup of liquids in high-speed flows, especially to inform defensive measures against chemical weapons. To conduct near-perfect initial interfaces, stabilized by surface tensions, physicists used droplet experiments with extraordinary space-time resolutions. The authors report their fourth investigation on the subject, this time with shear-thickening liquids, in Physics of Fluids.

Shear-thickening liquids are dense nanoparticle suspensions that increase in viscosity when deformed by a mechanical strain. The liquids analyzed in this study contained silica nanoparticles suspended in three concentrations of low molecular mass polyethylene glycol — thus achieving a range of shear-thickening rheologies. Laser-stimulated eosin dye enabled fine resolution fluorescent imaging of liquid drops exposed to aerobreakup in a shock tube.

Under different gas-flow conditions, detailed 3-D images revealed three regimes of aerobreakup, namely Rayleigh-Taylor piercing, Shear-Induced Entrainment (SIE) and Kelvin-Helmholtz SIE, and that they apply with appropriate accounting of the rheology based on what is known for viscous Newtonian liquids. Aerobreakup was arrested by shear-thickening, resulting in complex sequences of deformations and morphological evolutions. Actual breakup required much higher gas flows.

These data support both direct numerical simulations and effective field models that analyze the intermixing and dispersal of multiple materials treated as effective continua. The models are being used to address the problem of dispersal at very large scales, which are applicable to the practical scenarios of interest. The group is continuing to develop these practical tools to aid in understanding the consequences of chemical weapons and inform methods for defence in attack scenarios as well as for in situ defeat.

Source: “The physics of aerobreakup. IV. Strain-thickening liquids,” by V. V. Mitkin and T. G. Theofanous, Physics of Fluids (2017). The article can be accessed at https://doi.org/10.1063/1.4997009 .