Dynamics of a Passive Droplet in Active Turbulence

TL;DR

This study numerically investigates how a passive deformable droplet behaves in an active turbulent environment, revealing its deformation, movement patterns, and transition from ballistic to diffusive motion depending on droplet size.

Contribution

It introduces a coupled hydrodynamic and nematodynamic simulation framework to analyze passive droplet dynamics in active turbulence, highlighting size-dependent transition behaviors.

Findings

Droplet exhibits deformation fluctuations and run-and-stay movement patterns.

Transition from ballistic to diffusive motion depends on droplet size.

Velocity autocorrelation time increases as droplet size decreases below the active medium's length scale.

Abstract

We numerically study the effect of an active turbulent environment on a passive deformable droplet. The system is simulated using coupled hydrodynamic and nematodynamic equations for nematic liquid crystals with an active stress which is non-zero outside the droplet, and is zero inside. The droplet undergoes deformation fluctuations and its movement shows periods of ``runs" and ``stays". The mean square displacement of the geometric center of the droplet shows an extended ballistic regime and a transition to normal diffusive regime which depends on the size of the droplet. We relate this transition with a temporal scale associated with velocity autocorrelation function of the droplet trajectories, and with a spatial scale associated with one-time two-point velocity correlation function of the surrounding active medium. As the radius is decreased below the integral length scale, the velocity autocorrelation time of trajectories increases and the transition to normal diffusion is delayed.