Kelvin-Helmholtz Instability in Two Dimensional Semi-bounded Active Yukawa Liquids

Shear flows and the corresponding fluid instabilities are ubiquitous in nature - from astrophysical systems to bacterial dynamics. In a conventional medium, the free energy stored in the flow shear triggers a Kelvin-Helmholtz (KH) instability, which in turn grows and non-linearly saturates, leading to strong or weak turbulence.

In the present work, considering a two-dimensional semi-bounded cartesian domain, we systematically investigate the effect of activity, internal drives at the smallest scales of the system, on the growth, evolution, and saturation of KH instability, using Molecular Dynamics simulation[1], wherein a Yukawa liquid is used as a prototype. In particular, by increasing the percentage and the activity strength of the active particles, we demonstrate that activity increases the growth rate of the unstable spectrum[2]. Interestingly, it is found that the presence of activity not only alters the growth and the corresponding vortex dynamics, but also changes the bulk flow dynamics away from shear layers[2]. Our findings may have direct impact on a range of physics issues - from our understanding of biological active matter embedded in fluid flows to physics of mixing.