Spot formation in three-dimensional Yukawa liquid

Abstract

Dynamics of a three-dimensional (3D) plane Couette flow (PCF), which subjected to a 3D finite amplitude particle velocity perturbation, is addressed using 3D “classical first principles” molecular dynamics simulation with screened Coulomb potential or a Yukawa potential as the inter-particle interaction. Such systems are often realized in complex plasmas and charged colloids. Parameters are chosen such that the system is a Yukawa liquid whose kinematic viscosity is a time-dependent function of the particle correlation strength Γ controlled by shear heating. This feature is found to facilitate a unique quench study of the Reynolds number Re as a function of time for fixed system size and fixed flow speed. For small cross-sectional aspect ratios ∼20, starting from Re ∼ 1211-717, a laminar 3D PCF initial condition is shown to become unstable to localized 3D finite amplitude perturbation for various increasing amplitude strengths, clearly demonstrating the formation of a turbulent spot. This spot is found to spread in time into the otherwise laminar regions, a signature of subcriticality or co-existence of laminar and turbulent regions in PCF in a 3D Yukawa liquid. It is shown unambiguously that the range of interaction of Yukawa potential determines the nature of spot formation and its dynamics. At long range, a qualitative similarity of our results to those found in turbulent spots of PCF in conventional hydrodynamics is discussed. Our findings may have ramifications for a wide range of physical systems that exhibit sub-critical transition to turbulence.